A500 Power Supply whistle/High pitch sound

[jagLally]

My Amiga 500 power supply has started to make a whistling/high pitch sound. It doesn't happen every time I turn it on but it does happen frequently. I don't know the history of the power supply but it was stored in the loft for years I think. It's the heavy version.

Searching/reading around it looks like some capacitor(s) are probably leaking gas or something. I opened it up and after a clean, I can't see anything visually. Nearest I can tell is that the sound is coming from the big blue capacitors area.

I'm thinking I might as well replace all the capacitors as I managed to solder a replacement power switch on 1084 D1 recently. At least I won't have to open it up again.

I want to be sure I buy the right ones. I think the uF and Voltage and max temperature are the critical factors. The list is:
22uf 25v x 3 http://uk.farnell.com/panasonic-elec...f%2025v%20capa
4700uf 16v x 1 http://uk.farnell.com/panasonic-elec...v%20capacitors
4700uf 25v x1 http://uk.farnell.com/panasonic-elec...v%20capacitors
470uf 25v x 2 http://uk.farnell.com/panasonic-elec...v%20capacitors

The ones I can't determine are the three grey ones. My assumption is they are ceramic capacitors perhaps. Two of them have writing like:
Top:F 17 10-222
Side: 2200pFY 250v hmf
1000-8940. X2

and the bigger one:

0,1 uF x 2 MXT
HMF 250v SH
565-1 25/085/21

Would someone who knows what they are really doing be kind enough to:

1) check the links for the capacitors so that I'm ordering the right kind etc?
2) Give a link or a hint on what to order for the grey ones (pictures attached)?

[Daedalus]

For the electrolytics, the parameters you mention are critical indeed (though I tend to just go for 105 degree temperature rated parts for everything anyway), but you should also check the lead pitch as well since many values are available in a variety of pitches. Commonly they are 2.5mm, 5mm or 7.5mm, but there are also ~3.8mm parts available, and while a different pitch part will work fine, it won't be as neat having to bend the legs to suit.

As for the large grey capacitors, they're less likely to be the source of the whining as it's only really the electrolytics that dry out and cause performance issues, and the grey ones are just for suppressing noise on the mains side from what I can see (X and Y capacitors). I wouldn't worry about them for now, though if you did want to change them they're a special class of capacitor specifically for the task of EMI suppression, so don't just fit any capacitor that matches the ratings. They need to be (I presume) X2 and Y2 class capacitors. I don't have any links to hand, but they're pretty common for PSU applications so should be easy to find from any good electronics supplier.

[jagLally]

I’ll ignore the grey ones for now.

The links are all 105c rated. So I’m good there. Didn’t know about the pitch. I’ll double check that.

Thanks so much. You have been very helpful.

One final question: I was learning how to measure resistance (ohms) across capacitors using multimeter today and it all worked as described except for the two small grey ones. I couldn’t get a continuity beep either. Is that normal and I have to learn more to know the reason or are they faulty in some way?

[pandy71]

On your side i would also check inductances, usually those parts are responsible for audible sound not capacitors (capacitors may also produce sound but usually it is way weaker than sound produced by inductance) - after capacitor replacement sound may be still perceived - try to glue (epoxy resin) inductances (winding+carcass+core).

Grey ones are not a problem - only electrolytic capacitors may fail over time (i mean every part can fail but those grey are designed to not fail easily).

Resistance meter will give you no info about capacitor condition - to measure capacitor you need to use ohmmeter that use alternate current not DC to measure resistance - such specialized ohmmeters for capacitors are called ESR meter (ESR - Equivalent Series Resistance) - lack of response for grey ones is related to small capacitance for those capacitors - they are usually bellow 100nF - you may wish to use Mega-ohm range on ohmmeter but once again - they are not your problem - they filter very high frequencies and provide safety - better to not touch them with solder iron.

[jagLally]

Originally Posted by pandy71

On your side i would also check inductances, usually those parts are responsible for audible sound not capacitors (capacitors may also produce sound but usually it is way weaker than sound produced by inductance) - after capacitor replacement sound may be still perceived - try to glue (epoxy resin) inductances (winding+carcass+core).

Grey ones are not a problem - only electrolytic capacitors may fail over time (i mean every part can fail but those grey are designed to not fail easily).

Resistance meter will give you no info about capacitor condition - to measure capacitor you need to use ohmmeter that use alternate current not DC to measure resistance - such specialized ohmmeters for capacitors are called ESR meter (ESR - Equivalent Series Resistance) - lack of response for grey ones is related to small capacitance for those capacitors - they are usually bellow 100nF - you may wish to use Mega-ohm range on ohmmeter but once again - they are not your problem - they filter very high frequencies and provide safety - better to not touch them with solder iron.

Thanks. That explains a few things. I’ll be leaving those alone and just replace the normal capacitors.

[Daedalus]

Yep, as pandy71 says, resistance won't tell you much about a capacitor, especially not when it's still in the circuit. A capacitor will typically start with a low resistance and then increase to near infinite. How long that increase takes depends on the capacitance of the capacitor and your meter, but smaller values will be too fast to detect and so will appear infinite from the start. Being in a circuit makes this check (and many similar checks) less useful too because other parts in the circuit will also react to the meter and might give confusing readings.

[pandy71]

Originally Posted by jagLally

Thanks. That explains a few things. I’ll be leaving those alone and just replace the normal capacitors.

Do so and if sound will be still audible use 2 compound resin (epoxy) glue - try to stabilize inductances (transformer and inductors) - few glue drops should be sufficient - after time there is very high chance that glue used by manufacturer was fatigued and currently core and winding may move (minimally but still - magnetostriction and electrostriction can be very powerful - high currents, small elements) - this move create sound.

[E-Penguin]

I had a psu that made a weird whining sound. Then it caught fire. I'm no expert on these things but I can recommend either fixing or replacing it.

[pandy71]

Originally Posted by E-Penguin

I had a psu that made a weird whining sound. Then it caught fire. I'm no expert on these things but I can recommend either fixing or replacing it.

Well... please allow me to rewrite correctly your statement: you just ignored weird whining sound and despite malfunction tried to use PSU then after some time PSU just failed completely showing this trough some flames and smoke.

As far as i understand OT he is aware of PSU problem and he trying to address issue (fix PSU) by replacing capacitors which are most common source of failures in PSU's.
Original Amiga PSU is so simple that i can say it is good to start replacing faulty caps.

[E-Penguin]

Arrogant tit.

Capacitors are irrelevant to coil whine. If you're going to correct someone, at least be correct.

[pandy71]

Originally Posted by E-Penguin

Arrogant tit.

Capacitors are irrelevant to coil whine. If you're going to correct someone, at least be correct.

Thank you.

So please tell me what makes coil to whine?

[jagLally]

I've been into the retro scene since December 2017 and my experience is that everyone is helpful and polite. It's amazing and I've learned a lot from people here and I'm having a blast. It feels a bit like 'Life on Mars' if you have seen the BBC drama where a policeman seems to travel back in time.

I'm guessing that we are all of a certain age and probably with young kids. We should set an example with our behaviour.

Everyones post here has been helpful. So let's be friendly and polite to each other.

Back on topic:

Due to all the responses; I now have the capacitor list confirmed as correct. I also know why some capacitors couldn't be measured by the multimeter. I also have been made aware of the winding making a noise and it may not be capacitors after all or at least not the full story.

As a final test before fixing anything, I've re-assembled the power supply and tightened everything and plugged it back in. Absolutely no noise so far . I'm monitoring it very carefully. I'm beginning to wonder if it was just something loose resonating internally or externally. Observer and monitor for now.

[pandy71]

I didn't mean to insult anyone especially E-Penguin, well yes, i've tried to be funny and a bit of ironic (being from almost 20 years electronics engineer i've had impression that have some basic knowledge about PSU's and related areas) but just a little bit so this reaction was a bit surprising - anyway - sorry E-Penguin - it was not my intention to insult You, please accept my apologies...

Why it doesn't sound after reassembly - it can be many reasons - like some mechanical stress that apply some pre-tension on PCB and prevent inductance to being loose - hard to say with close inspection - usually it is recommended to resolder all soldering point in case of cold junction - especially heavy elements (like transformers, big caps coils connectors) are tend to loose integrity - this is PSU is over 25 years old and everything is possible.