Adrian: I used to design video drivers for CRTs back in the 1970s. The chief problem one faces is the slowness of response of the output transistor. In order to minimize parasitic collector to base capacitance and eliminate its multiplication by what is called the *Miller effect*, a technique is used, The output of the transistor collector is to the tube and has an inductor as well as resistor to rail to sharpen the response, but the base is grounded, and the input goes to the EMITTER.. This is called a *common base*, or *cascaded* configuration. We used it to multiply voltage, but not current. In essence two transistors are used to make one, with overall lower parasitic capacitance and higher voltage capabilities than either alone.. The old vacuum tube design of this was called a 'cascode' . I think it might have been from 'cathode to anode' or maybe 'cascaded cathode'. If you haven't seen this arrangement before, you will get puzzling voltages. There will be no signal on the base, and very little voltage change on the emitter either. Because what is changing is the CURRENT. I can't describe this well in words. But googling common base or cascade schematic should bring up some examples that make it all clear. It is a technique that one only finds when transistors are being pushed to the limit of what they will do. I met it first in driving a head up display CRT for fighter aircraft in the 1970s. The video signal needed to go to 75MhHz I think, and that was really hard with the transistors of the day. Whereas a typical TV video signal is only 5-8MHz. That we could do easily. 75MHz was the bleeding edge and I never quite made it, but my boss took what I had done and added some emitter followers to it and made the spec. Just.
Egad, man. You've brought back some memories here of working on the SPA-4 Plan Position Indicator. It had the "cascoded" arrangement you describe here. (I haven't touched one of these old beasties since I left "A" School.)
I've fixed a bunch of tube guitar amps, and I can tell you that many many times I've unplugged the tubes, plugged them back in again and the amp comes to life. Those pins get oxidized.
Sometimes for the mysterious process of self-healing to be instigated, machines just need to know they’re in a safe space and that they’re with someone who understands and cares about them. Adrian seems to be excellent at facilitating this🙏🤷♂️🕯️
It is more common than you expect: repair services have this problem all the time, sometimes just the movement of the device to the repair shop and change in temperature fix the problem temporally making it difficult to spot. A classical percussive treatment and a few days turned on can help but not always. Sometimes is electric, some capacitors self heal after being used for instance. It is particularly common in old semiconductors.
I am convinced there was some sort of cold solder joint or something on the neck board. These types of PCBs are notorious for that. Back in the day when I troubleshot the issue to a particular circuit, I would reflow all of the components in that circuit.
There is a bad solder joint next to Q401, follow the trace going right from the base pin, and to the pad that is left of the R411 silk screen, and you can see two pins that appear to touch, connecting the Collector and Base together (probably just perspective) but the pad connecting the trace to the collector looks like it's a cruddy cold solder joint. Maybe working in that area to remove and reinstall Q401 reflowed it?
Good catch! Indeed, the connection from the collector of Q401 to R411 looks like a cold joint (on the resistor, not on the transistor). As the trace between them is very short, un/resoldering Q401 might have reflowed that enough to make it work. A lot of the solder joints look bad in the picture but this one in particular looks like it did not wet the resistor pin correctly (32:39).
@@EdwinSteiner it may also have not reflowed it enough and it could fail again in the future. Maybe he could unsolder that leg of the resistor and see if it recreates the original fault?
There is a possibility that q401 was installed wrong at the factory. He removed it and tested it and reinstalled it. So he could of put it back in the correct way.
13:00 When you touched the neckboard it moved. "Glue did nothing so let's pull that off". If the Neckboard was loose from be jostled, maybe one of the pins wasn't making a good connection or was oxidized?
Not done with the video yet, but this is fascinating. New-Old-Stock can 1.) just be an artifact that was ALWAYS defective, sometimes new products needed to be RMA-ed and never were! 2.) something aged poorly wherever this was stored in whatever conditions, causing a problem. 3.) it might have been New-Old-Stock, but that doesn't mean it wasn't kicked around, damaged in the years through many moves through different storage places, perhaps very unceremoniously once it was obvious it was going to be un-sold merchandise.
I gotta say it's amazing the amount of effort you went to to show the audience what you are doing. The editing of this video could not have been easy. Great video Adrian.
The base of the video driver transistor has a capacitor to ground. This would conduct any video to ground so the the base voltage of the transistor is a constant DC level. If that capacitor was shorted or leaking, it would have pulled the base DC toward ground and stopping the transistor from passing video to the CRT cathode. I would suspect the capacitor as the monitor was sitting unused for such a long time. Thanks for the great videos.
Not quite. An emitter follower is where the signal goes into the base and the output is on the emitter, with the collector tied to a fixed voltage. This is also called a common collector circuit, because the collector is common to the input and output. When the signal goes into the emitter, the base is tied to a fixed voltage, and the output is on the collector. This is known as a common base amplifier, and is mainly used for low-impedance, high bandwidth circuits. The circuit with the two transistors in the schematic is a cascode circuit. The first transistor is a common emitter stage, from which the output on the collector feeds into the emitter of the second stage. Since the base of the second transistor is at a fixed voltage, the emitter is the same, and this doesn't vary with the signal. The point of this is that with the base at a fixed voltage, the voltage swings on the collector doesn't couple capacitively to the base, and conversly the collector of the first transistor doesn't have a swing, so there's nothing to feed back into the base. This results in a circuit with high bandwidth and useful voltage and current amplification.
I have a Dell crt monitor from the early 2000s where the brightness and the color go in and out. If I tap on the top of it sometimes it will go back to the correct brightness. Sometimes I get a blue tint and sometimes a pink tint. I suspect a loose connection. This video makes me think of it.
Agree on that, "L" should be an inductor coil. But also the poking test should have made it fail again (unless the inductor was not poked hard enough)..
The voltage on the base of the cathode drive transistor is probably a supply rail that also powers the collector of the small transistor. The small transistor is an amplifier for the DC signal of the contrast pot. So the small transistor isn't even driving the base of the big one.
That’s what I was thinking as well, I‘ve seen this happen (with used monitors, but that have seen long periods of being stored without being powered on)
@@peterhanraets Especially since it had never been turned on before. Still pretty dry probably so probably still a good idea to change the ones that are under stress.
I'm not so good at analogue electronics either. A transistor is easy enough to understand, but it gets confusing when it's the PNP variant rather than NPN, or when it's used in "unusual" ways. Anyway, a thought came to me. Some people have mentioned that capacitors stop functioning properly when they haven't been subjected to voltage/use for a long time. It has something to do with the oxide layer inside. I noticed there's a capacitor in the circuit at the base of that transistor. Maybe tinkering with the circuits, making measurements and subjecting components to heat made this capacitor repair itself. I have no idea, but it was a thought. Congrats either way, on making the thing work again.
Did you check out the functioning of the 7406? This is not a 'standard' Inverter TTL logic chip like the 7407. The output is Open Collector (Buffer/Driver) so you won't just get a logic voltage on its output, it needs a resistor or something it can drive current into. (Up to 30V)
Sometimes just jolting a device or parts around will reconnect something that had degraded over time. Taking it apart and putting it back together probably reconnected something.
Adrian, it's possible that the transistor was not soldered correctly. Removing it and then resoldering it seemed to solve the problem. Reflowing the solder points for each component might also help.
Its possible the signal was being shunted to ground somewhere. Zieners can have some odd failure modes. But its very possible the a small solder blob made it from the wave solder. Moving board around board knock it off. Zieners are resistors until they reach their breakdown voltage. Sometimes they are faulty and breakdown sonner. This drops voltage lower than what they were designed to control.
If I had to foster a guess I'd say that some of the capacitors had lost their forming layer. Over the process of "fixing" the monitor the capacitors reformed allowing normal function. Beyond that I didn't see anything that might have fixed the problem.
Most likely there was a cracked solder joint on Q401. If the circuit to the base of Q402 was open (which would explain the +5v on the base) it would not drive anything as Q402 pulls the video signal low from +55v down to the video white level (which you control by the contrast). Q401 is responsible for biasing the cathode drive transistor to either a 'dim' or a 'hot' level depending on the contrast control and the intensity bit. If it's disconnected, there would be no current flowing through the base of Q402 and no video drive.
That looks like something added by an external program. The lines are over the entire screen. Microsoft Powertools has a feature that can do it (mouse crosshairs)
I think I have read somewhere that sometimes heating a failing transistor can "revive" it. Maybe the act of unsoldering and resoldering it has "fixed" it.
Who loves CRTs more than Adrian? I just finished vacuuming out and cleaning and successfully testing a 12" toshiba crt in a recent video. After all the hard work it actually just powered up and worked. However after all my work it still stunk of animal piss which I knew it would. Still it powered up one last time.
26:40 probably to increase rise time, or if they only needed 2 drivers, use them all in parallel to prevent them from interfering/floating/oscillating etc. I think I read an article in Elektor way back that some tin can transistors (usually germanium) can form conductive filaments with age, used or new/unpowered. These can self heal when used. It could be one of those cases and might explain why at first it didn't work while the filaments were dissolving and started to work. It just might've been enough to leave the monitor running for a couple of hours and it would pop back to life. The monitor is unused so unless there's oxidation due to high humidity storage conditions, cracked PCB, dry joints etc issues that occur during use are unlikely. Not sure if the same can happen with electrolytic capacitors might be able to reform when not in use for a long time. My first suspect was the tin can transistor when I saw in in the footage. But it's hard to fault find/pin point if it self heals something else was going on. That's life I guess, of electronics repair.
You’d can’t specialize in everything; your repair skills in repairing old PCs is remarkable. My only comment would be unplug an re-plug connections on thing that have been sitting got years before you even power it up. And an active component failing with barely any use beyond typical factory tested by is exceedingly rare
In your initial assessment of the unit you missed the final troubleshooting step, bc 90% of all electronic failures are a bad connection, whack it on the side.
120 isn't the worst, but I get it. You have to give a disclaimer, since you don't know who is watching this channel. You get all sorts of people doing bizarre things. I watch shango do his thing all the time. Bob Anderson also. Common sense is priceless when you work with any electronics.
Finding a fault that isn't there is tricky! Good video. Perhaps a mirror on the back of the bench might help? Maybe a shaving mirror - if you have one?
If the contrast potentiometer was a 3 pin, is it possible the monitor was plugged in wrong from the start? Was it a 3 min connector, or a 2 min? Was hard to tell, as it was buried.
Might I recommend you create title cards with your disclaimers on them for display as needed? According to the manual for the Zoyi ZT-703S, it's scope input is good for 150 v at X1, 300 v at X10.
hey ive been watching ur mac vids and ive tried everything i can according to forums dead mac scrolls and anything else but i have a vertical collaspse or just a bright soild line across the screen but when u up the voltage it makes a constatnt beeping noise and im stumped
In my experience a 100x probes are not cheap as you say: more expensive a cheap $70 scope: about $100 to $200 here in my country as a cheap scope is $200: and a 100x probe is not a thing you want to save money on as your life may depend on it and the life of your equipment too. I prefer probes without switches so you can not damage accidentally the scope, in 1x/10x is not much of a problem, that is why 100x probes are just 100x. As many scopes does not have the 100x modes you must make usually put in 10x and divide by 10 what you see. I wouldn't save on the probes there are $50 probes that go to 2kV but I am not sure I trust them.
Why does it seem like power supplies have their traces just any old place? They're curved, they're bulbous, they have no rhyme or reason in the way it's organized in such a way that it just looks like blobs of PCB traces. I'm sure there has to be a reason for this, but I don't actually understand what they're doing.
Similar to gauge of wire, fat traces for more watts. Traces are after all "flat" wires and width is the only way to get fatter gauge-equivalent. Also some designs use that copper to help absorb heat off the pins of certain heat generating devices. And many board designs make the ground fill up all remaining space for RFI reasons (same for having smooth curves vs sharp corners, especially with high voltages and AC), and to ensure there is adequate grounding for everything that needs it (since electrons "flow" from ground to the positive). Usually you want a fatter ground than the sum total of all the positive wires (or, traces). If it's just one power connection like a Molex on an old hard drive then both being the same gauge is fine, once there are multiple paths then it gets more complicated.
@@Spudz76 I found it, and ordered one. about 110 Canadian, but still cheap. I saw a review of the previous model and it had a few issues, but they seem to be mostly fixed in the newer one
Adrian: I used to design video drivers for CRTs back in the 1970s. The chief problem one faces is the slowness of response of the output transistor. In order to minimize parasitic collector to base capacitance and eliminate its multiplication by what is called the *Miller effect*, a technique is used, The output of the transistor collector is to the tube and has an inductor as well as resistor to rail to sharpen the response, but the base is grounded, and the input goes to the EMITTER..
This is called a *common base*, or *cascaded* configuration. We used it to multiply voltage, but not current. In essence two transistors are used to make one, with overall lower parasitic capacitance and higher voltage capabilities than either alone..
The old vacuum tube design of this was called a 'cascode' . I think it might have been from 'cathode to anode' or maybe 'cascaded cathode'.
If you haven't seen this arrangement before, you will get puzzling voltages. There will be no signal on the base, and very little voltage change on the emitter either. Because what is changing is the CURRENT.
I can't describe this well in words. But googling common base or cascade schematic should bring up some examples that make it all clear. It is a technique that one only finds when transistors are being pushed to the limit of what they will do. I met it first in driving a head up display CRT for fighter aircraft in the 1970s. The video signal needed to go to 75MhHz I think, and that was really hard with the transistors of the day. Whereas a typical TV video signal is only 5-8MHz. That we could do easily. 75MHz was the bleeding edge and I never quite made it, but my boss took what I had done and added some emitter followers to it and made the spec. Just.
Egad, man. You've brought back some memories here of working on the SPA-4 Plan Position Indicator. It had the "cascoded" arrangement you describe here. (I haven't touched one of these old beasties since I left "A" School.)
I've fixed a bunch of tube guitar amps, and I can tell you that many many times I've unplugged the tubes, plugged them back in again and the amp comes to life. Those pins get oxidized.
@@messmer777 knee high to "have you tried turning it off and back on again?"
Ok, Adrian, here's your book title: The Art of Getting Electronics to Fix Themselves
Guess he has the IT aura. I have that too. Basically people have issues and when you get there, it works now.
Perhaps when desoldering and resoldering, you reflowed a bad joint?
You are the King of Self-Healing devices. I don't like not knowing what a fault really was either.
Sometimes for the mysterious process of self-healing to be instigated, machines just need to know they’re in a safe space and that they’re with someone who understands and cares about them. Adrian seems to be excellent at facilitating this🙏🤷♂️🕯️
It is more common than you expect: repair services have this problem all the time, sometimes just the movement of the device to the repair shop and change in temperature fix the problem temporally making it difficult to spot. A classical percussive treatment and a few days turned on can help but not always. Sometimes is electric, some capacitors self heal after being used for instance. It is particularly common in old semiconductors.
32:51 The Base of Q401 seems to have a dry solder joint. The actual Base pin seems to be completely lacking solder.
The leg of R411 attached to the collector looks pretty iffy too.
I dunno, Q401 base looks like a normal joint to me
What I don't like is all the corrosion around R410 and R414
@@jwhite5008 Do you think that is corrosion or dry flux?
I am convinced there was some sort of cold solder joint or something on the neck board. These types of PCBs are notorious for that. Back in the day when I troubleshot the issue to a particular circuit, I would reflow all of the components in that circuit.
There is a bad solder joint next to Q401, follow the trace going right from the base pin, and to the pad that is left of the R411 silk screen, and you can see two pins that appear to touch, connecting the Collector and Base together (probably just perspective) but the pad connecting the trace to the collector looks like it's a cruddy cold solder joint. Maybe working in that area to remove and reinstall Q401 reflowed it?
Good catch! Indeed, the connection from the collector of Q401 to R411 looks like a cold joint (on the resistor, not on the transistor). As the trace between them is very short, un/resoldering Q401 might have reflowed that enough to make it work. A lot of the solder joints look bad in the picture but this one in particular looks like it did not wet the resistor pin correctly (32:39).
@@EdwinSteiner it may also have not reflowed it enough and it could fail again in the future. Maybe he could unsolder that leg of the resistor and see if it recreates the original fault?
There is a possibility that q401 was installed wrong at the factory. He removed it and tested it and reinstalled it. So he could of put it back in the correct way.
13:00 When you touched the neckboard it moved. "Glue did nothing so let's pull that off". If the Neckboard was loose from be jostled, maybe one of the pins wasn't making a good connection or was oxidized?
Not done with the video yet, but this is fascinating. New-Old-Stock can 1.) just be an artifact that was ALWAYS defective, sometimes new products needed to be RMA-ed and never were! 2.) something aged poorly wherever this was stored in whatever conditions, causing a problem. 3.) it might have been New-Old-Stock, but that doesn't mean it wasn't kicked around, damaged in the years through many moves through different storage places, perhaps very unceremoniously once it was obvious it was going to be un-sold merchandise.
I gotta say it's amazing the amount of effort you went to to show the audience what you are doing. The editing of this video could not have been easy. Great video Adrian.
The base of the video driver transistor has a capacitor to ground. This would conduct any video to ground so the the base voltage of the transistor is a constant DC level. If that capacitor was shorted or leaking, it would have pulled the base DC toward ground and stopping the transistor from passing video to the CRT cathode.
I would suspect the capacitor as the monitor was sitting unused for such a long time.
Thanks for the great videos.
Thought so too. Maybe cap(s) needed some time to reform.
Am i the only one who thinks it's funny that they used RGB colored wires to drive the neck-board on a monochrome monitor?
Prob same production line parts.
yeah, made me chucle too
@CybAtSteam back in those days they would use all white wires in a pinch. Do love the irony though. Good catch.
That type of transistor circuit where the signal is fed into the emitter is called an emitter follower.
Not quite. An emitter follower is where the signal goes into the base and the output is on the emitter, with the collector tied to a fixed voltage. This is also called a common collector circuit, because the collector is common to the input and output.
When the signal goes into the emitter, the base is tied to a fixed voltage, and the output is on the collector. This is known as a common base amplifier, and is mainly used for low-impedance, high bandwidth circuits.
The circuit with the two transistors in the schematic is a cascode circuit. The first transistor is a common emitter stage, from which the output on the collector feeds into the emitter of the second stage. Since the base of the second transistor is at a fixed voltage, the emitter is the same, and this doesn't vary with the signal. The point of this is that with the base at a fixed voltage, the voltage swings on the collector doesn't couple capacitively to the base, and conversly the collector of the first transistor doesn't have a swing, so there's nothing to feed back into the base. This results in a circuit with high bandwidth and useful voltage and current amplification.
Not really a no-name. I have 6 Scepter LCD Monitors purchased over the last couple of years. They really are very nicely made.
A lesser known or value name, yes. But they did earn market share. Definitely NOT no-name.
Again, something loose such as those connectors? Well, we all learning from trial and error, sometimes things just heal itself without reason.
There's a reason. We just don't know what it is.
Those amber monitors were the best really when it comes to monochrome with a black background.
I have a Dell crt monitor from the early 2000s where the brightness and the color go in and out. If I tap on the top of it sometimes it will go back to the correct brightness. Sometimes I get a blue tint and sometimes a pink tint. I suspect a loose connection. This video makes me think of it.
32:19 - Some of those solder connections look a bit dodgy. Note the dark rings around the leads. Look at the upper lead of L401.
Agree on that, "L" should be an inductor coil. But also the poking test should have made it fail again (unless the inductor was not poked hard enough)..
The voltage on the base of the cathode drive transistor is probably a supply rail that also powers the collector of the small transistor. The small transistor is an amplifier for the DC signal of the contrast pot. So the small transistor isn't even driving the base of the big one.
Those solder joints all look like a reflow wouldn't hurt. 🤭
I really do love how you spend the time working the stuff out, I feel like I'm right there next to you. ❤
R411 solder joints look pretty suspect. I bet the monitor was a warranty return from a dealer that tried it before they shipped it or bundled it.
Looks like those sleeping capacitors reformed after so many years sitting in a box.
Well, glad it works again 👍👏
Could it be that some capacitors re formed while the monitor was plugged in for a longer period of time.
That’s what I was thinking as well, I‘ve seen this happen (with used monitors, but that have seen long periods of being stored without being powered on)
@@peterhanraets Especially since it had never been turned on before. Still pretty dry probably so probably still a good idea to change the ones that are under stress.
I'm not so good at analogue electronics either. A transistor is easy enough to understand, but it gets confusing when it's the PNP variant rather than NPN, or when it's used in "unusual" ways. Anyway, a thought came to me. Some people have mentioned that capacitors stop functioning properly when they haven't been subjected to voltage/use for a long time. It has something to do with the oxide layer inside. I noticed there's a capacitor in the circuit at the base of that transistor. Maybe tinkering with the circuits, making measurements and subjecting components to heat made this capacitor repair itself. I have no idea, but it was a thought. Congrats either way, on making the thing work again.
Did you check out the functioning of the 7406? This is not a 'standard' Inverter TTL logic chip like the 7407. The output is Open Collector (Buffer/Driver) so you won't just get a logic voltage on its output, it needs a resistor or something it can drive current into. (Up to 30V)
its amazing how many things fix themselves Adrian LOL
Sometimes just jolting a device or parts around will reconnect something that had degraded over time. Taking it apart and putting it back together probably reconnected something.
Adrian, it's possible that the transistor was not soldered correctly. Removing it and then resoldering it seemed to solve the problem. Reflowing the solder points for each component might also help.
A slight possibility is that some tiny conductive piece was in the slot of one of the spark gap capacitors and shook loose.
Its possible the signal was being shunted to ground somewhere. Zieners can have some odd failure modes. But its very possible the a small solder blob made it from the wave solder. Moving board around board knock it off. Zieners are resistors until they reach their breakdown voltage. Sometimes they are faulty and breakdown sonner. This drops voltage lower than what they were designed to control.
I may have zeiner's backwards. I sometimes do that. But either way they pull to a certain voltage and stop. Sometimes they don't stop.
If I had to foster a guess I'd say that some of the capacitors had lost their forming layer. Over the process of "fixing" the monitor the capacitors reformed allowing normal function. Beyond that I didn't see anything that might have fixed the problem.
Most likely there was a cracked solder joint on Q401. If the circuit to the base of Q402 was open (which would explain the +5v on the base) it would not drive anything as Q402 pulls the video signal low from +55v down to the video white level (which you control by the contrast). Q401 is responsible for biasing the cathode drive transistor to either a 'dim' or a 'hot' level depending on the contrast control and the intensity bit. If it's disconnected, there would be no current flowing through the base of Q402 and no video drive.
Wonder if a capacitor reformed? How did you get that cool x/y line display in Google Photos at @40:05 ?!
That looks like something added by an external program. The lines are over the entire screen. Microsoft Powertools has a feature that can do it (mouse crosshairs)
My thought was a dry solder joint somewhere.
@@K-o-Ryeah, there was some dirty solder joints in that area. Could have been hiding a bad joint.
This happend to me as well, didnt start but after being connected to power for awhile it turned right on
Just introducing heat can sometimes do wonders.
@21:00 my guess is C204, it's always a crapacitor.
I think I have read somewhere that sometimes heating a failing transistor can "revive" it. Maybe the act of unsoldering and resoldering it has "fixed" it.
Who loves CRTs more than Adrian? I just finished vacuuming out and cleaning and successfully testing a 12" toshiba crt in a recent video. After all the hard work it actually just powered up and worked. However after all my work it still stunk of animal piss which I knew it would. Still it powered up one last time.
Coffee grounds?
Ozone generator?
26:40 probably to increase rise time, or if they only needed 2 drivers, use them all in parallel to prevent them from interfering/floating/oscillating etc.
I think I read an article in Elektor way back that some tin can transistors (usually germanium) can form conductive filaments with age, used or new/unpowered. These can self heal when used. It could be one of those cases and might explain why at first it didn't work while the filaments were dissolving and started to work. It just might've been enough to leave the monitor running for a couple of hours and it would pop back to life. The monitor is unused so unless there's oxidation due to high humidity storage conditions, cracked PCB, dry joints etc issues that occur during use are unlikely.
Not sure if the same can happen with electrolytic capacitors might be able to reform when not in use for a long time.
My first suspect was the tin can transistor when I saw in in the footage. But it's hard to fault find/pin point if it self heals something else was going on. That's life I guess, of electronics repair.
I'm gonna put my money on unplugging and re-plugging the neckboard is what fixed it. 40 years of oxidation on those CRT pins.
You’d can’t specialize in everything; your repair skills in repairing old PCs is remarkable. My only comment would be unplug an re-plug connections on thing that have been sitting got years before you even power it up. And an active component failing with barely any use beyond typical factory tested by is exceedingly rare
In your initial assessment of the unit you missed the final troubleshooting step, bc 90% of all electronic failures are a bad connection, whack it on the side.
not a cracked solder joint on Q401, but maybe a cold solder joint?
120 isn't the worst, but I get it. You have to give a disclaimer, since you don't know who is watching this channel. You get all sorts of people doing bizarre things. I watch shango do his thing all the time. Bob Anderson also. Common sense is priceless when you work with any electronics.
Maybe its a case of old hardware being giving care.
Pocus Focus? 😁
32 bottles of green ketchup, 7 staples.
Finding a fault that isn't there is tricky! Good video. Perhaps a mirror on the back of the bench might help? Maybe a shaving mirror - if you have one?
I'd have started troubleshooting with a bit of "percussive maintenance" =P
Maybe the capacitors reconditioned themselves?
Adrian is a literal miracle worker 😁
feels like a non-essential component failed short and eventually failed open.
If the contrast potentiometer was a 3 pin, is it possible the monitor was plugged in wrong from the start? Was it a 3 min connector, or a 2 min?
Was hard to tell, as it was buried.
Might I recommend you create title cards with your disclaimers on them for display as needed?
According to the manual for the Zoyi ZT-703S, it's scope input is good for 150 v at X1, 300 v at X10.
It's always fun when things fix themselves. Then, after some time, they do it again :)
And please learn to draw a PNP transistor ;)
20:25 - OOPS! They GROUNDED the OUTPUTS of the unused inverters on IC201 ! (pins 6, 10 and 12)
You disconnected and reconnected the neck board.
Sir, you have a luck coefficient much larger than mine. Enjoy. No worries.
Most people accidentally break stuff, you accidentally repair stuff..🤔😁
hey ive been watching ur mac vids and ive tried everything i can according to forums dead mac scrolls and anything else but i have a vertical collaspse or just a bright soild line across the screen but when u up the voltage it makes a constatnt beeping noise and im stumped
Maybe there was some debris in the potentiometer and you cracked it lose?
R411 looks very badly soldered. It might be intermittent.
Replace that small transistor, later it will fail open again.
Capacitor Reform maybe?
I though I could see dry joints on Q401
suprised you didnt deoxit the connector
The video I just watched was about fixing an ice maker on another channel of yours.
Hmmm I love when things fix themselves 😂
Capacitor reforming after all those years???
maybe some bad capacitor (phantom short) reformed and woke up ??
dry joints?
In my experience a 100x probes are not cheap as you say: more expensive a cheap $70 scope: about $100 to $200 here in my country as a cheap scope is $200: and a 100x probe is not a thing you want to save money on as your life may depend on it and the life of your equipment too.
I prefer probes without switches so you can not damage accidentally the scope, in 1x/10x is not much of a problem, that is why 100x probes are just 100x. As many scopes does not have the 100x modes you must make usually put in 10x and divide by 10 what you see.
I wouldn't save on the probes there are $50 probes that go to 2kV but I am not sure I trust them.
It's amazing how many times talking apart a non-working piece of electronics and reassembling it fixes, something??? 🙂
Why does it seem like power supplies have their traces just any old place? They're curved, they're bulbous, they have no rhyme or reason in the way it's organized in such a way that it just looks like blobs of PCB traces. I'm sure there has to be a reason for this, but I don't actually understand what they're doing.
Similar to gauge of wire, fat traces for more watts. Traces are after all "flat" wires and width is the only way to get fatter gauge-equivalent. Also some designs use that copper to help absorb heat off the pins of certain heat generating devices. And many board designs make the ground fill up all remaining space for RFI reasons (same for having smooth curves vs sharp corners, especially with high voltages and AC), and to ensure there is adequate grounding for everything that needs it (since electrons "flow" from ground to the positive). Usually you want a fatter ground than the sum total of all the positive wires (or, traces). If it's just one power connection like a Molex on an old hard drive then both being the same gauge is fine, once there are multiple paths then it gets more complicated.
Probably a dry joint
>Sceptre
>No name
Bruh
My my my... Adrian, 2 things: 1. you have a laying on hands capability, and 2., your oscilloscope probes and soldering iron are magic wands!
which scope is that? Looks like it says Zoyi?
There are lots of almost identical scopes. I have the XEAST XE 703S with 2 channels. Works great and was less than $80
There is an older video review of it (and some others), search.
@@Spudz76 I found it, and ordered one. about 110 Canadian, but still cheap. I saw a review of the previous model and it had a few issues, but they seem to be mostly fixed in the newer one
Thank you for your hard work and dedication. Your videos are always a joy to watch.🌱☺️😱
L401 looks bad joint.
ADRIAN MAGIC GO! (੭• o•)੭✩₊˚.⋆☾⋆⁺₊✧
gremlin
Continue to delight us with your incredible ideas. Your videos are a gift!👾🌝🤪