Vacuum Tube Power Supply Hum Troubleshooting - McIntosh MX110
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- เผยแพร่เมื่อ 6 ก.ย. 2024
- BG269 - How to troubleshoot a power supply hum issue. In this case we had an issue with a McIntosh MX110 (non-Z model). But the steps are the same, regardless of the type of gear.
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Interesting video thanks. I wear rubber gloves and performed the same one hand in the pocket, my dad showed this to me when I was watching him repair TV (tube) set. Explained the capacitor cage and that caps hold a charge just like a battery. Credit to Benjamin Franklin for that who upon seeing a bunch of capacitors, to which he remarked it “…It looks similar to a battery of canons…”. How the term became associated with a Voltiac pile is another story.
The old adage of checking values of components doesn’t preclude premature failure.
He is a great teacher, I would have like to take electronic classes with him.
Mark - a tried and proven troubleshooting technique that was illustrated. Definitely value added. Take care and stay safe during this unsettled times. Best, Don
Its interesting that the new capacitor failed in such a short time. This has actually happened to me 3 times in my career. QC hasn't been that good from the source of manufacture. Had to send back a few already. Either way, you can't overlook new components as being the culprit. Good video. Stay safe Mark.
An old ham friend of mine taught me this trouble shooting technique many years ago...and you are quite correct, if you don't know what your doing...do not attempt...could make for a very bad day! I'm also surprised you are ordering the same capacitor/manufacture...I would replace all those cans as you will possibly go down this road again...its not worth trying to keep the integrity of a vintage chassis to forsake durability...Once bit, never stick your hand inside the fence again 😎
Well, that's a fairly significant "ding" on CE Manufacturing capacitors. I know... you only hear and remember the negative anecdotes but this is a very high-end capacitor from a would-be reputable manufacturer. I'm sure it was just a fluke... but it has me wondering. Thanks for the video Mark!
Great fault finding and explanation. Thanks for sharing your knowledge.
That waveform tells there is low impedance (quick) charging of some bus capacitor, followed by too fast discharge. The discharge rate and the classical exponential shape tells that either there is very little capacitance OR THAT there is leakage/much load current.. On an RC chain, I would measure AC voltages at each capacitor section. It should reduce towards the end of the chain in rather regular fashion. But then I would measure the voltage drop over each of the segment to next resistors and calculate the current in each. If there are no loads attached to the intermediate taps, then the current should be the same throughout the chain. A leaky section would be indicated by a step reduction of the current. If there are loads from various taps, the calculations require measuring those load currents at some resistor likely existing in the side load branch. But the biggest often ignored capability of a modern digital multimeter is the ability to measure AC ripple on top of DC voltage. Some fancier ones even have a dual display, where you can see both AC and DC at the same time.
I noticed that many Mcintosh MX-110z units after they got updated, the capacitor with values of 50mfd by 4 @350dcv is on the right (when looking at the unit from the front), why is your 50mfd by4 at 350DCV is on the left? Is this the reason for early failure? I thought I had heard from you that it is important match the recommended capacitance of the RC chain, since this could effect the voltage drop down the drain.
Thank you in advance...Reality is getting to be too much...I need to relax for 20 minutes, thank you again.
Excellent repair! I just don't want to test those filter caps with power on. I just use cap-meter and esr-meter. Thanks
Mark great video, haven't seen this method in a long time, very effective. Thank you for helping to develop basic troubleshooting skills.
This was a really good video Mark. Like these! More of them please.
amazing video, please upload more of this
That was a show of how smart you are .I am looking at N elecrichome PA- 300 . Would please do a video on this amp
Rubber gloves never hurt when doing the capacitor tests and the other hand in your pocket
Glad you found time to post, good way to do it!
I would have used the o scope to test each section of the power supply to try and locate the source of the hum,then once i found which section was the source ,then i would use the scope to individually check each cap and resistor to try and locate the origin,tho i might end up having to remove the cap to verify the fault,which you did not have to do with your external cap trick.
Made to Mallory specs on Mallorys original equipment, yeah that figures, always were a problem, I tried to stick with Sprague or Cornell Dubs.
Wouldn’t it be easier if you suspect a bad capacitor to test the b+ rail for ac voltage with the dmm?
Yes and a lot faster too. It's a test for AC ripple on a DC voltage.
Scope shows classic output from bridge rectifier with inadequate capacitance across it. Can't believe that McIntosh didn't use a filter choke -- especially at the prices they charge(d). My $99 Dynakit Stereo 70 had a large choke and no hum.
It seems more likely that the fault was in the connection to the common negative (can.) It could be the wiring to the +85 or I have seen the connection from the can itself to the internal common negative go bad. If you look at the bottom of the can, around the phenolic insulator where the + terminals come out, you should be able to see a small tab that just barely sticks out from under the edge of the metal can. That tab is the conductor to the common negative for the multiple capacitors inside. I've "repaired" failures like this by hitting the can above the tab with a center punch, but it's hard to defend that as a long term solution. I don't understand how they make that connection reliable. Perhaps it's spot welded, but there's never any sign of this in the alum above.
It would have been easy to sort this out with a few quick touches of your scope probe.
Would like to take the old capacitor can apart to see if cheap no-name Chinese capacitors are used ? or quality Japanese capacitors are used ? Or if they just had a bad solder connection inside the can?
randomlyselecteduser Thanks I miss that wording .
randomlyselecteduser the build process looks really cool.
Real good video Mark
Nice amp. My vintage 1956 Harman Kardon A250 Epic has a Hum also was fine till recently happens only in phono and when my hand is near a certain area it is not as loud as that more like a 60hz Hum and gets louder when hand gets closer. When touch metal anywhere Hum goes away
Mi Mark, on the MX-110, what’s the best way to convert line level output sources and using it with the tape head input on the MX-110? I need more line level inputs, I know the aux and tape monitor inputs can be used as line level, but the MX-110 has sweet tube circuitry and I hate to let go to waste. Thanks in advance. BTW, I love watching your videos.
Greetings:
I am sorry, but I do not know how you can NOT start by scoping the power supply at the rectifiers immediately. I understand that to create a two level output on the b+. Since you have a power transformer, by isolating the safety ground and all output grounds, you can even tie that floating 85v artificial ground and connect your scope ground to that point and even measure both b+ and b- relative to it. I assume your using that t4st cap to connect the 85v point to ground has a similar affect you still should be doing scoping instead of meter measurements. Hope you checked that new cap b4 installinng it. I was screaming at you to show us all power supply cap signals, aarg!
Hi Mark, I noticed that many Mcintosh MX-110z units after they got updated, the capacitor with values of 50mfd by 4 @350dcv is on the right (when looking at the unit from the front), why is your 50mfd by4 at 350DCV is on the left? Is this the reason for early failure? I thought I had heard from you that it is important match the recommended capacitance of the RC chain, since this could effect the voltage drop down the chain.
Hello! interesting video, as an amateur I immediately thought that it must be a filter capacitor after you stated that the frequency of the noise was 120hz.
Rectified 60hz should give 120hz hum without filtering?
Or is there something else that could potentially create this particular frequency in the circuit?
Electromagnetic interference should have a lower frequency right?
Best regards, Victor.
I had a CP manufacture multi can went bad after 5 months. Just because it is "new' manufacture, doesn't mean is it better. :)
Great video, but that 't' you put on the end of "across" for some reason is like nails on a chalkboard ;-) Keep up the great work, though. It really was an interesting video that I watched from start to end.
Why did it go bad though? Manufacturing fault or over voltage? It would be interesting to do an autopsy. One other possible cause of 100/120hz ripple is a short....DA.
Where can I track down a service manual or the schematic diagram for MX-110? Thanks in advance.
great tutorial and explanation
I put one of those caps in a Dynaco ST70 for someone and it came back with the cap completely open. as if the ground inside the cap opened.
Can you open the bad cap to see how it is built inside?
Mark, I have a similar problem with the Millard 5-20 amp that I just completed , I am getting the same loud hum , tried changing all the caps but the hum stays the same, no change, any suggestions ..
Thanks
I own a Leak Point One Stereo 20 valve pre amp and the valve amp that goes with it! Obviously I want the amplifier section to look original which brings me to my question! Instead of buying a 4 in 1 capacitor, why not leave the original in place and disconnect it then buy 4 separate capacitors of the same value and solder them in place using the original as an anchor point only? The effect is the same and if a new capacitor goes bad, it's easier to replace just one capacitor rather than the whole can capacitor on top! I said to my tech here in Australia where I live that I wanted the original capacitors left in place and solder in new capacitors underneath because the 2 capacitors on top are the same colour as the amp itself! I've seen a few problems like this with these new four in one jobs and if you have to drill the rivets out to replace it, it's a real pain! By isolating the problem with this Macintosh amp using a Nichicon cap and an alligator clip, it proves my point! I've seen some woeful restores where techs cut the can in half and stick 4 caps inside it and it looks just awful! Yes, there are situations in old tube gear where you do have to install new tube sockets and safer wiring etc but when it comes down to aesthetics where the amplifier is on display, I don't want two bloody big holes in the amplifier when you can install new ones underneath. When I have friends around, they drool at my restored Leak gear! The power and output transformers in this amp weigh a ton and with removable jumpers to select voltage and speaker impedance, only a fool could make a mistake with this amp! I hope Covid-19 takes a hike! Wearing these masks everyday is becoming tedious as you mentioned! Cheers from down under, Andrew Peter Collins!
Great repair tip!
Very organised, work bench indeed sir.👈😒
I have the same humming sound, on my Copland CTA 501.
Don't be critical the amplified just wants to hum along to the tune hahah cheesy ones are the best
Anybody had any experience with dirac live with tube amplifiers! it should work really well tighten Up the Bass better synergy
You could have used a signal tracer would have giving you the characteristics of the capacitor slope. Maybe there's capacitors are not that reliable long-term use
I wonder if some other issue caused the cap to overstress.
I'm very surprised you got another capacitor from the same place as the bad one when it's pretty much obvious they are stuffing cheap China type parts into these cans when these caps should have lasted another 25 years. You should open the can of the bad one and show your viewers what quality is being used in these replacements to save others the same trouble you went through if indeed they are low quality replacements. Thanks anyway
Great job how can I fix my amp the Hum happens in phono only if touch metal no more hum
You can che k for bad caps by checking leakage to ground???
Great video! Why do you think that new capacitor failed so quickly?
Them caps are rubbish had 3 go bad in a row and just ended up using separate caps and tag strip
It is much safer and simple to use an ESR meter.
Awesome!!!!
Don't you just hate it when Hum Pixies get inside your capacitors. It's a real problem with these large capacitors because they build their nests in them and then you can never get the pixies out. It's even worse if they get inside a transformer because they can eat through the wire.
Why is it specifically a 120 Hz hum? Seemingly a 2x multiplier of the North American AC frequency...
Full wave bridge rectifier output is 120 hz ripple.
Радиола "Ригонда". :)
what was that sound when you plugged in the speaker terminal? Sounds like feed back to my uneducated ears. I have a amp that does this. Should it be something to be concerned about?
You mean the loud crackling at 4:20? That happend because an RCA jack makes contact with the hot pin before connecting to ground. It's just heavy noise induction. That's why you should at least turn the volume complete down before connecting thing, even better to turn the unit off. But these days, you can also get RCA plugs with a spring loaded ground sleeve that makes contact first and then moves a bit back to get the hot pin in.
Any warranty on the capacitor?
I had one section go bad within a day or so with this same brand capacitor. I have been reluctant to use them again since is it so time consuming to change them.
I was reluctant to use them 40 years ago, always had lots of problems when it was Mallory, suddenly open was a common thing.
Thanks for the insight! I would be too afraid to hook up the test cap live..... :-0)) Mark.
A seasoned technician is not supposed to spend hours to detect an obvious problem.
sounds like 120 hz
Greetings:
I am sorry, but I do not know how you can NOT start by scoping the power supply at the rectifiers immediately. I understand that to create a two level output on the b+. Since you have a power transformer, by isolating the safety ground and all output grounds, you can even tie that floating 85v artificial ground and connect your scope ground to that point and even measure both b+ and b- relative to it. I assume your using that t4st cap to connect the 85v point to ground has a similar affect you still should be doing scoping instead of meter measurements. Hope you checked that new cap b4 installinng it. I was screaming at you to show us all power supply cap signals, aarg!
Wouldn’t it be easier if you suspect a bad capacitor to test the b+ rail for ac voltage with the dmm?
Wouldn’t it be easier if you suspect a bad capacitor to test the b+ rail for ac voltage with the dmm?
You will get varying results in doing so.