Thank you for the video, it is always interesting to see old tech analyzed and troubleshooted. A few observations: 1. You cannot test an SCR with the multimeter because of the Ihold parameter, that is the minimum required load current to maintain the SCR active after the gate has been triggered. The multimeter simply does not have enough current on the diode function for the SCR's needs. But even if it would have had it, you still couldn't have tested the SCR just with the multimeter because it needs it's gate triggered before you can see anything with the multimeter. The same reason it why the SCR cannot be tested with the component tester. The easiest way is with a lab power supply capable of constant current, you first set the output voltage above the gate trigger voltage of the SCR, then you set the constant current at some hundreds of mA ( let's say 0,5A ). You connect the power supply directly across the A and K of the SCR then with some resistor you connect the gate to the Anode ( the plus output of the PSU, thus you trigger the gate and the SCR should short the PSU's output if it is ok ( with 0,5A output current the SCR cannot be damaged but it should be enough to keep the SCR active ). 2. Whenever i see tantalum caps on any board, the first thing i do even before powering it up to see if it works or not, i test all the tantalums on the board, just because they are the type of caps that fail the most and they do it by shorting them selves out. I know they are the best in some regards, but still in all my designs i always avoid tantalums at any cost ( and i do design new stuff quite allot ). That is always a good way to start other troubleshooting vids, you know they are the most likely to fail so you check them before doing anything else. A question: -Can you please let me know where you got that electronic load? It seams not only interesting, but quite useful ( for me at least ) if it does test battery cells...
Thank you so much for the explanation! It makes sense. The link to the electronic load is in the description. I've read some bad things about them - obviously there are hundreds of copycats around. Mine is rated 180W, I tested it with 180W for some time and it never failed. I did "tweak" it by replacing thermal paste and adding a small heatsink on the only diode. I find it amazing, it saves me so much time and - most importantly - allows me to test rails up to 180W with just a few clicks: no piles of scorching hot resistors and melting leads on my workbench! :) Tantalums: You are right. I shall do that next time! The burning diode fooled me! :)
@@tony359 you are welcome as always! PS: I have just ordered the electronic load ( thanks for the link and comments on it ). It almost seams too good to be true :) I mean, the amount of bang for buck is... Granted it is not a professional tool, it isn't RS or other top quality brands, but still, 50$ ( that is how much i just paid for it, including shipping ) for an electronic load that cand do CC CR CP and CV and all those crazy stuff... unreal :)
@@tony359 Hello! Not sure if you will read this comm, but i did receive my electronic load yesterday and it does seam to do most of what it claims, which is great! Didn't had time to test all it's functions but the most important stuff does checks out so, it great. Really testing battery capacity is something i've been lacking thus far, but not any more, so again thank you for the video and for showing us the electronic load and where it can be found! PS: One maybe small concern about it is that it has only one power transistor for the load baring part, and a rather small case ( TO247 ). Not sure what type it is though ( Mosfet, IGBT or BJT ). If it is a mosfet then i am not sure how it could safely handle the 180W claimed, because most of the power mosfets have very poor SOA at medium to high VDS, which is normal since they are designed to work as switching devices. Even if it is a BJT, it is still quite difficult to keep it in the safe region at such high power, and maintain a safe TC... Some of the more expensive BJT's from Onsemi do seam to handle it, but only just. Hmm, i wonder... could we hack it? 🤔 Could we add one more power transistor in parallel with the one on the electronic load? If it is a mosfet, then doubling the gate charge and CISS/COSS/... could be a problem for the control part, could it? Not sure... Maybe it's something worth investigating. Please let me know if you read this. All the best.
@@tony359 Very ahead of its time, though. Apple with this drive decided against using a separate disk controller and instead integrated one into the drive itself- an industry first in 1981. With this they were able to add extensive self-diagnostics and provide just a simple parallel interface to the computer itself- very much like modern IDE/ATA drives work.
Old electronics: Step 1 remove Rifa's Step 2 check tantalum's But as you said checking the board if a short is gone is something that can easily been overlooked. Interesting repair again.
Lesson learnt! That said, if I had checked the pads, I would have assumed one of the diode's legs were tied to ground and it was normal? Who knows. Thankfully I had plenty of diodes! Thank you and thanks for watching!
The "AC OK" makes a lot of sense on a HDD power supply: While the normal "POWER GOOD" signal indicates that the DC voltages are OK, the "AC OK" signal is intended to say "bad" as soon as possible when AC fails (e.g. when you unplug the device, or when you turn off a power switch upstream of the supply), even when the charge in the capacitors is still sufficient to sustain a stable output voltage for some 100s of a second. The point is that an early AC failure indicator enables the HDD controller to possibly finish writing one sector, including the correct CRC, and then (most important!) park the heads of the drive using the remaining charge in the capacitors of the supply. Generally, an AC OK signal is common on hardware that needs to take some emergency action in case of sudden AC failure. I happened to have a chat with the manufacturer of the SOHO PBX we used for 15 years. They explained that they detect a single missing cycle of AC, and in case of failure, the entire non-volatile state of that device is transferred from RAM to EEPROM before the DC fails, so for example no toll records got lost on AC failure.
That makes very much sense, thank you for taking the time to share that with me. It's so impressive that a few 100s of a microsecond might be enough to save the day!
@@tony359 Oops, that "few 100s of a microsecond" is nonsense. I intended to write about a duration of something like 10ms to 100ms. So this was meant to be "few 100s of a *second*". I fixed it.
99% of switching power supplies have loads built into the power supply itself. You don't need to put external loads. If the power supply is protected, all the primary part is working and you don't need to check all that. The safest is a shorted diode at the output. And it's the first thing you should check.
Well, Apple Macintosh's switching power supplies definitely don't like being powered up without a load, voltages were all over the place! I could have tested without, I just chose the safer side and added some. You're right about checking the primary - my bad, but won't hurt :) Thanks for your input and for watching!
10:20: If you get that ticking noise from an SMPS, you don't have to check the primary power components for shorts. If they are short, you get a bang and/or a blown fuse. That kind of ticking indicates either the operating voltage of the primary side is failing, or a short on the secondary side. 16:20: Capacitance might vary with operating voltage. So getting 56µF at 3V doesn't mean you won't get just 47µF at 250V. Depending on the measurement mode, excessive leakage current can cause a false might reading of the capacity. If the capacitors lost their formation due not being used in a long time, excessive leakage current is quite normal. So there are multiple causes for a unexpected high capacity displayed on your tester which do not indicate imminent failure of the caps.As long as the ESR of the caps is fine, don't worry about them. 1 Ohm ESR on high-voltage electrolytics is very much OK. 30:25: This should be your main take-away from this repair: Silicon diodes are quite robust devices. They usually fail for a reason, they don't just happen to fail for nothing. Diodes are usually specified for a maximum junction temperature (the temperature of the silicon piece in the diode) of 175°C, because at higher temperatures, they turn into a short circuit - just like your diode did. So if a diode is short, you always should probe the circuit around it with extreme prejudice for causes that could overload the diode. Missing a shorted capacitor after a shorted diode is a rookie mistake, but don't worry, everyone started as rookie.
Noise: You are totally right. In fact, I thought about that at some point but the video was already edited... :) Capacitance: Great to know. I didn't know the capacitance could change with voltage, that explains many things. Diodes: another awesome new thing to learn! Again, thank you for taking the time to share your experience, I do appreciate it a lot. And thanks for watching!
The component tester was likely having trouble testing it because SCR’s have a holding current and also the tester was likely not driving the gate hard enough either. Smaller SCRs may work ok and ones with “sensitive gates” they may also show up as a transistor with and Hfe (gain) of 1
Those capacitors that are showing over their stated capacity are probably electrically leaky. Caps which are electrically leaky will leak their charge at an accelerated rate and confuse component testers into thinking they're a higher capacity than they really are. Leakage testers aren't really common anymore, so you either have to get a really old unit and restore it, or design one yourself. I think Mr. Carlson over at Mr. Carlsons' lab designed one for his patreon supporters a long time ago, might be something to look into.
@@tony359 For the price point those Chinese component testers go for, they're fine if you know their limitations and quirks. My only complaints about them is they'll get confused on some component IDs, have no input protection (really easy to kill them with capacitors) and sometimes have weird quirks. I've accidentally killed several of these things with partially charged capacitors, they really do not have any input protection, just some passives between the MCU and the socket. I have one of the more advanced testers with a color screen, and I've found that it can't identify a 47uF capacitor of any brand, type or voltage, it just thinks nothing is connected.
A thyristor has THREE p-n junctions (p-n-p-n) and cannot be tested using ordinary multimeters. Component testers usually can't test them as well: thyristors require a certain amount of current to be held in the open state.
You mean the primary ones? Good idea. Maybe they would read better after a few hours of use. I am familiar with the reforming process, it just takes quite a lot of time :) Thanks for watching!
Hi, I wonder were can I find the schematics for the power supply for the Lisa profile, mi Lisa profile power supply has some rifa capacitors blown and I can’t identify the part number Please help
I'm sorry, I am not familiar with the Lisa. Maybe you can find some pictures online or ask the Apple Vintage community? The valued for those caps should not be hugely critical, their purpose is to filter off the noise coming from the PSU back into the mains network.
Those secondary capacitors are not in great shape. 0.2 ohm is too high for a generic 1000uF 16V capacitor, and way too high for a low-ESR one. The output rails might be a bit noisier than desirable. Also, these early 105°C capacitors have a tendency to piss on the board, better to prevent it. While you can leave the electrolytics alone if they test OK-ish and does not leak, dipped tantalums that are older than 25 years are a matter of replace-on-sight in my book. I've seen so many stuff with tantalum mass failures that it does not worth the risk to leave old tantalums in circuit. A few years ago I got hold of a video waveform monitor. I saw it was full of tantalums, but I wanted to test it. All the tantalums were on the 5V and +/-12V rails, which were supplied by 78/79xx regulators, so I wasn't risking damaging things if a tantalum shorts. There were about 15pcs 10uF 16V tantalum in the thing. The first shorted in the first second. Thankfully it smoked, so it was easy to spot which one failed. I cut it out, and switched the monitor back on. I was never able to get the CRT up to temperature, because one more tantalum failed at each attempt. I've seen similar things in other instruments multiple times. Only epoxy dipped/plastic encapsulated tantalums are affected. If you see a metal encapsulated dry tantalum, you can leave it alone, they practically never fail, even after 40-50 years. Also, always buy tantalums only from reputable sellers. Never use NOS tantalums, because they degrade in storage (that's why you should by only from replutable sellers, because smaller shops/ebay might give you 30 years old ones). Nowadays, if I see a tantalum that was used only for power rail bypass, I usually substitute them with a low-ESR electrolytic, because they are a lot less likely to short out in the future, and are a lot cheaper. Up to 1...4.7uF MLCCs can be used, or film capacitors (4.7uF 50/63V is available in RM5 package). But I try not to use high capacity MLCCs if not necessary, because their most common failure mode is short circuit, just like tantalums'. But at least they are not aging in storage, AFAIK. If a tantalum is in a timing circuit or signal path, unfortunately you should replace it with an other tantalum, although you can substitute it with a film capacitor if it fits, but definitely not with an electrolytic or MLCC, because their temperature stability is a lot worse compared to tantalums.
Thanks for the input, really appreciated! I'd agree that on a 40 years old board replacing capacitors can only be a good thing. I didn't realise 0.2Ohm was too much for a 1000uF, thanks for that. The owner of the unit said he would re-cap himself if needed. On the tantalum... you know, I thought about that. I should have replaced the other one too! I realised when it was too late! My friend will likely replace that too. On "reputable sellers"... it's not easy. Here in the UK there is not much left. You can buy from RS Components or similar but prices are high and you get charged extra if you don't spend at least £20 (CPC). Ebay is... ebay, I know. But sometimes I don't feel like spending £30 for a few capacitors so I end up on Ebay. I know it's risky. I believe I got those tantalum's from ebay some time ago. Again, they would cost me an arm and a leg from a proper seller - and sometimes I don't want to wait until I have a bigger shopping cart. But you are totally right! I'll bear in mind the options you mentioned on replacing tantalums on next occasion! Thank you a lot!
i don't care how good of a brand of caps they are, how well they test on the simple LCRs like those, after 30 years, and some flavor of component failure, they get replaced. there's a chance they're leaking voltage that the simple LCR testers won't show. that said, i'll usually give the better brands a lot more time leeway than the cheaper brands. cheap ones are rated to 15y max for me, and the really cheap ones are replace on sight, regardless, if repairs are occuring. something like this? full recap, no questions.
I agree with you, I normally replace capacitors on all my old gear. That said, it's got a bit difficult in the UK to get electronic components. There is often a minimum order from large suppliers and for small quantities it can get expensive. So it depends how much I care of something but as a general rule I like to replace them regardless. This drive is 40 years old, it can't hurt to replace those caps! :) Thanks for watching!
Thank you for the video, it is always interesting to see old tech analyzed and troubleshooted.
A few observations:
1. You cannot test an SCR with the multimeter because of the Ihold parameter, that is the minimum required load current to maintain the SCR active after the gate has been triggered.
The multimeter simply does not have enough current on the diode function for the SCR's needs.
But even if it would have had it, you still couldn't have tested the SCR just with the multimeter because it needs it's gate triggered before you can see anything with the multimeter.
The same reason it why the SCR cannot be tested with the component tester.
The easiest way is with a lab power supply capable of constant current, you first set the output voltage above the gate trigger voltage of the SCR, then you set the constant current at some hundreds of mA ( let's say 0,5A ).
You connect the power supply directly across the A and K of the SCR then with some resistor you connect the gate to the Anode ( the plus output of the PSU, thus you trigger the gate and the SCR should short the PSU's output if it is ok ( with 0,5A output current the SCR cannot be damaged but it should be enough to keep the SCR active ).
2. Whenever i see tantalum caps on any board, the first thing i do even before powering it up to see if it works or not, i test all the tantalums on the board, just because they are the type of caps that fail the most and they do it by shorting them selves out.
I know they are the best in some regards, but still in all my designs i always avoid tantalums at any cost ( and i do design new stuff quite allot ). That is always a good way to start other troubleshooting vids, you know they are the most likely to fail so you check them before doing anything else.
A question:
-Can you please let me know where you got that electronic load?
It seams not only interesting, but quite useful ( for me at least ) if it does test battery cells...
Thank you so much for the explanation! It makes sense. The link to the electronic load is in the description. I've read some bad things about them - obviously there are hundreds of copycats around. Mine is rated 180W, I tested it with 180W for some time and it never failed. I did "tweak" it by replacing thermal paste and adding a small heatsink on the only diode. I find it amazing, it saves me so much time and - most importantly - allows me to test rails up to 180W with just a few clicks: no piles of scorching hot resistors and melting leads on my workbench! :)
Tantalums: You are right. I shall do that next time! The burning diode fooled me! :)
@@tony359 you are welcome as always!
PS: I have just ordered the electronic load ( thanks for the link and comments on it ).
It almost seams too good to be true :)
I mean, the amount of bang for buck is... Granted it is not a professional tool, it isn't RS or other top quality brands, but still, 50$ ( that is how much i just paid for it, including shipping ) for an electronic load that cand do CC CR CP and CV and all those crazy stuff... unreal :)
Same feeling I had when I discovered it. I thought "I need one!". Glad the video was useful!
@@tony359 Hello!
Not sure if you will read this comm, but i did receive my electronic load yesterday and it does seam to do most of what it claims, which is great! Didn't had time to test all it's functions but the most important stuff does checks out so, it great. Really testing battery capacity is something i've been lacking thus far, but not any more, so again thank you for the video and for showing us the electronic load and where it can be found!
PS: One maybe small concern about it is that it has only one power transistor for the load baring part, and a rather small case ( TO247 ).
Not sure what type it is though ( Mosfet, IGBT or BJT ).
If it is a mosfet then i am not sure how it could safely handle the 180W claimed, because most of the power mosfets have very poor SOA at medium to high VDS, which is normal since they are designed to work as switching devices.
Even if it is a BJT, it is still quite difficult to keep it in the safe region at such high power, and maintain a safe TC...
Some of the more expensive BJT's from Onsemi do seam to handle it, but only just.
Hmm, i wonder... could we hack it? 🤔
Could we add one more power transistor in parallel with the one on the electronic load?
If it is a mosfet, then doubling the gate charge and CISS/COSS/... could be a problem for the control part, could it?
Not sure...
Maybe it's something worth investigating.
Please let me know if you read this.
All the best.
Wow, that was an unexpected hard drive design! Great job fixing the power supply!
Such a waste of space for only 5MB :D Thanks for watching!
@@tony359 Very ahead of its time, though. Apple with this drive decided against using a separate disk controller and instead integrated one into the drive itself- an industry first in 1981. With this they were able to add extensive self-diagnostics and provide just a simple parallel interface to the computer itself- very much like modern IDE/ATA drives work.
Cool drive! great repair, well done Tony!
Thank you!
Old electronics:
Step 1 remove Rifa's
Step 2 check tantalum's
But as you said checking the board if a short is gone is something that can easily been overlooked.
Interesting repair again.
Lesson learnt! That said, if I had checked the pads, I would have assumed one of the diode's legs were tied to ground and it was normal? Who knows. Thankfully I had plenty of diodes! Thank you and thanks for watching!
Thoroughly enjoyed the diagnostic process. Thank you!
Thank you for watching!
The "AC OK" makes a lot of sense on a HDD power supply: While the normal "POWER GOOD" signal indicates that the DC voltages are OK, the "AC OK" signal is intended to say "bad" as soon as possible when AC fails (e.g. when you unplug the device, or when you turn off a power switch upstream of the supply), even when the charge in the capacitors is still sufficient to sustain a stable output voltage for some 100s of a second. The point is that an early AC failure indicator enables the HDD controller to possibly finish writing one sector, including the correct CRC, and then (most important!) park the heads of the drive using the remaining charge in the capacitors of the supply.
Generally, an AC OK signal is common on hardware that needs to take some emergency action in case of sudden AC failure. I happened to have a chat with the manufacturer of the SOHO PBX we used for 15 years. They explained that they detect a single missing cycle of AC, and in case of failure, the entire non-volatile state of that device is transferred from RAM to EEPROM before the DC fails, so for example no toll records got lost on AC failure.
That makes very much sense, thank you for taking the time to share that with me. It's so impressive that a few 100s of a microsecond might be enough to save the day!
@@tony359 Oops, that "few 100s of a microsecond" is nonsense. I intended to write about a duration of something like 10ms to 100ms. So this was meant to be "few 100s of a *second*". I fixed it.
"a split second" will also work ;) Thanks for clarifying!
99% of switching power supplies have loads built into the power supply itself. You don't need to put external loads.
If the power supply is protected, all the primary part is working and you don't need to check all that. The safest is a shorted diode at the output. And it's the first thing you should check.
Well, Apple Macintosh's switching power supplies definitely don't like being powered up without a load, voltages were all over the place! I could have tested without, I just chose the safer side and added some. You're right about checking the primary - my bad, but won't hurt :)
Thanks for your input and for watching!
10:20: If you get that ticking noise from an SMPS, you don't have to check the primary power components for shorts. If they are short, you get a bang and/or a blown fuse. That kind of ticking indicates either the operating voltage of the primary side is failing, or a short on the secondary side.
16:20: Capacitance might vary with operating voltage. So getting 56µF at 3V doesn't mean you won't get just 47µF at 250V. Depending on the measurement mode, excessive leakage current can cause a false might reading of the capacity. If the capacitors lost their formation due not being used in a long time, excessive leakage current is quite normal. So there are multiple causes for a unexpected high capacity displayed on your tester which do not indicate imminent failure of the caps.As long as the ESR of the caps is fine, don't worry about them. 1 Ohm ESR on high-voltage electrolytics is very much OK.
30:25: This should be your main take-away from this repair: Silicon diodes are quite robust devices. They usually fail for a reason, they don't just happen to fail for nothing. Diodes are usually specified for a maximum junction temperature (the temperature of the silicon piece in the diode) of 175°C, because at higher temperatures, they turn into a short circuit - just like your diode did. So if a diode is short, you always should probe the circuit around it with extreme prejudice for causes that could overload the diode. Missing a shorted capacitor after a shorted diode is a rookie mistake, but don't worry, everyone started as rookie.
Noise: You are totally right. In fact, I thought about that at some point but the video was already edited... :)
Capacitance: Great to know. I didn't know the capacitance could change with voltage, that explains many things.
Diodes: another awesome new thing to learn! Again, thank you for taking the time to share your experience, I do appreciate it a lot. And thanks for watching!
Amazing repair... those tantalums are killing all the 8-bit fun 😀
Imagine a world without tantalums.... so boring :D Thanks for watching!
Try adding some oil to the stepper motor bearing on the hard drive. It seems to be sticking during the startup seek tests.
Thank you. I'll mention my friend who will have a chance to plug it to an actual system for testing!
amazing video, Tony, i really do enjoy them!
Thank you!
Hey Tony, great job. looking below I see you have the eye of some excellent fellow creators
I do and I feel very fortunate! :) Thanks for watching!
I love the smell of the flux in the morning! Or in the evening... BTW Nichicon's capacitors are reliable, as you can see even above the tolerance ;)
Can't argue with that! :)
Thank you for the video! Very fun to watch.
Thank you for watching!
The component tester was likely having trouble testing it because SCR’s have a holding current and also the tester was likely not driving the gate hard enough either. Smaller SCRs may work ok and ones with “sensitive gates” they may also show up as a transistor with and Hfe (gain) of 1
Thank you! I'll keep that in mind! Thanks for watching!
Well done with the repair! I have an Apple /// - and a Profile adapter card. But am missing a Profile drive... ;-)
The /// with the Profile becomes quite a big tower of old goodness :) Thanks for watching!
Interesting repair, always helps to have the circuit diagram to see whats going on :)
Particularly for an amateur like me they're critical! Thanks for watching!
A fun watch, as always!
Thank you!
Those capacitors that are showing over their stated capacity are probably electrically leaky. Caps which are electrically leaky will leak their charge at an accelerated rate and confuse component testers into thinking they're a higher capacity than they really are.
Leakage testers aren't really common anymore, so you either have to get a really old unit and restore it, or design one yourself. I think Mr. Carlson over at Mr. Carlsons' lab designed one for his patreon supporters a long time ago, might be something to look into.
Indeed I'm aware the tester I have is more a toy than anything else. I'll check Mr. Carlson's device, thanks for the hint.
@@tony359 For the price point those Chinese component testers go for, they're fine if you know their limitations and quirks.
My only complaints about them is they'll get confused on some component IDs, have no input protection (really easy to kill them with capacitors) and sometimes have weird quirks.
I've accidentally killed several of these things with partially charged capacitors, they really do not have any input protection, just some passives between the MCU and the socket.
I have one of the more advanced testers with a color screen, and I've found that it can't identify a 47uF capacitor of any brand, type or voltage, it just thinks nothing is connected.
Yes, I damaged one myself with a large capacitor. The IC exploded :)
very well done again, your video is most educating and entertaining! also i had never seem one of them before, five mb oh my.
One MB per chilo! :) Thank you and thanks for watching!
Awesome Sleuthing Tony, well done. What is up with the goves?
Thank you! Nothing, I thought it was a good idea when handling stuff full of chemicals and lead! :)
A thyristor has THREE p-n junctions (p-n-p-n) and cannot be tested using ordinary multimeters. Component testers usually can't test them as well: thyristors require a certain amount of current to be held in the open state.
Great to hear! Well it’s easy to do that after all! Thanks for watching!
Thanks for the video.
Thank you for watching!
Maybe those caps weren't getting enough voltage? Therefore they couldn't reform? Tech Tangents has a great video on capacitor reforming.
You mean the primary ones? Good idea. Maybe they would read better after a few hours of use. I am familiar with the reforming process, it just takes quite a lot of time :)
Thanks for watching!
Reforming caps isn't worth it!
They will never be as reliable as a new one.
And new ones are still quite affordable.
I guess it might be worth for those *very* old machines with shiny capacitors where replacing them with modern ones would honestly look wrong.
thank you great video i enjoyed watching
Thank you!
Hi, I wonder were can I find the schematics for the power supply for the Lisa profile, mi Lisa profile power supply has some rifa capacitors blown and I can’t identify the part number
Please help
I'm sorry, I am not familiar with the Lisa. Maybe you can find some pictures online or ask the Apple Vintage community? The valued for those caps should not be hugely critical, their purpose is to filter off the noise coming from the PSU back into the mains network.
Have you given it back to your friend yet? Does it work?
Not yet, still sitting on a shelf! 🙂 thanks for watching!
Do you use the gloves to prevent electric shocks? Because thats nitrile / rubber, that dont guide current.
No, it was just to keep my hands clean 🙂 Thanks for watching!
You sure got a lot of resistors now...
I have a wide selection of high power resistors for testing loads and also sound amplifiers. But the digital load is so convenient! :)
i was talking about the ones you harvested from the board, but the electronic one is nifty too :D@@tony359
Those secondary capacitors are not in great shape. 0.2 ohm is too high for a generic 1000uF 16V capacitor, and way too high for a low-ESR one. The output rails might be a bit noisier than desirable. Also, these early 105°C capacitors have a tendency to piss on the board, better to prevent it.
While you can leave the electrolytics alone if they test OK-ish and does not leak, dipped tantalums that are older than 25 years are a matter of replace-on-sight in my book. I've seen so many stuff with tantalum mass failures that it does not worth the risk to leave old tantalums in circuit. A few years ago I got hold of a video waveform monitor. I saw it was full of tantalums, but I wanted to test it. All the tantalums were on the 5V and +/-12V rails, which were supplied by 78/79xx regulators, so I wasn't risking damaging things if a tantalum shorts. There were about 15pcs 10uF 16V tantalum in the thing. The first shorted in the first second. Thankfully it smoked, so it was easy to spot which one failed. I cut it out, and switched the monitor back on. I was never able to get the CRT up to temperature, because one more tantalum failed at each attempt. I've seen similar things in other instruments multiple times. Only epoxy dipped/plastic encapsulated tantalums are affected. If you see a metal encapsulated dry tantalum, you can leave it alone, they practically never fail, even after 40-50 years.
Also, always buy tantalums only from reputable sellers. Never use NOS tantalums, because they degrade in storage (that's why you should by only from replutable sellers, because smaller shops/ebay might give you 30 years old ones). Nowadays, if I see a tantalum that was used only for power rail bypass, I usually substitute them with a low-ESR electrolytic, because they are a lot less likely to short out in the future, and are a lot cheaper. Up to 1...4.7uF MLCCs can be used, or film capacitors (4.7uF 50/63V is available in RM5 package). But I try not to use high capacity MLCCs if not necessary, because their most common failure mode is short circuit, just like tantalums'. But at least they are not aging in storage, AFAIK. If a tantalum is in a timing circuit or signal path, unfortunately you should replace it with an other tantalum, although you can substitute it with a film capacitor if it fits, but definitely not with an electrolytic or MLCC, because their temperature stability is a lot worse compared to tantalums.
Thanks for the input, really appreciated! I'd agree that on a 40 years old board replacing capacitors can only be a good thing. I didn't realise 0.2Ohm was too much for a 1000uF, thanks for that. The owner of the unit said he would re-cap himself if needed.
On the tantalum... you know, I thought about that. I should have replaced the other one too! I realised when it was too late! My friend will likely replace that too.
On "reputable sellers"... it's not easy. Here in the UK there is not much left. You can buy from RS Components or similar but prices are high and you get charged extra if you don't spend at least £20 (CPC). Ebay is... ebay, I know. But sometimes I don't feel like spending £30 for a few capacitors so I end up on Ebay. I know it's risky.
I believe I got those tantalum's from ebay some time ago. Again, they would cost me an arm and a leg from a proper seller - and sometimes I don't want to wait until I have a bigger shopping cart. But you are totally right!
I'll bear in mind the options you mentioned on replacing tantalums on next occasion! Thank you a lot!
i don't care how good of a brand of caps they are, how well they test on the simple LCRs like those, after 30 years, and some flavor of component failure, they get replaced. there's a chance they're leaking voltage that the simple LCR testers won't show.
that said, i'll usually give the better brands a lot more time leeway than the cheaper brands. cheap ones are rated to 15y max for me, and the really cheap ones are replace on sight, regardless, if repairs are occuring.
something like this? full recap, no questions.
I agree with you, I normally replace capacitors on all my old gear. That said, it's got a bit difficult in the UK to get electronic components. There is often a minimum order from large suppliers and for small quantities it can get expensive. So it depends how much I care of something but as a general rule I like to replace them regardless. This drive is 40 years old, it can't hurt to replace those caps! :)
Thanks for watching!
$3400! wow! Bloody hell thats expensive for only 5MB. Did anyone actually buy it at that price.
Of course! That was 1981. A 5MB HDD at that time would be like buying a 100TB HDD today :)
nice joob
Thank you!
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