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replacing all the capacitors

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Dwight Elvey

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Hi
I see this over and over. "I think I need to replace all the capacitors in my machine because it isn't working".
Ok, how many times has one replaced the capacitors and got a working machine when done?
A single shorted capacitor is relatively easy to spot but replacing them all, I question.
Lets see a vote.
Dwight
 
With old Macs? Like, 90% of the time. The other 10%, the damage from the leaking caps was too bad and ruined the logic board.

With Sun SPARCstation IPCs? 100% of the time after a power supply recap. This happened in the worst of them: https://imgur.com/a/OTZiH0y

IBM PS/2 floppy drives are now getting to the point where I just recap them, whether they work or not. Pentium 4 motherboards, too (I still have cause to fix these for $day_job clients now and then, they seem to have been in the middle of the "cap plague" era for the most part).

Any time I end up replacing all of the caps on the board, it's one of two things: caps that show signs of obvious damage (leaking, board was run really hot, cracked RIFA caps, etc.), and tantalum caps on boards that have shown extremely high tendencies for random cap explosions. North Star S-100 boards are, in my experience, one of those cases where all of the caps get replaced. I've ran them on the current limited supply for many hours, then transferred them to the IMSAI where they ran fine for many more hours, and then one morning they let go.

I know what you're getting at though, it's a knee-jerk thing for folks who have machines that don't work.
 
It's a common reaction to any kind of problem with older electronics, not just computers -- it's today's equivalent of the common thought decades ago that the solution for any kind of problem with vacuum-tube electronics was "maybe it needs new tubes", even though many kinds of tubes rarely fail.

Ironically, people who are knowledgeable about electronics had to go through several decades of explaining that if you turn on an old radio and all you hear from the speaker is a loud hum, the problem is probably that the capacitors have gone bad, not the tubes.

It seems that a generation of people latched onto that nugget of wisdom and now assume that 1.) it applies to all problems with all kinds of older electronics, and 2.) that if you don't replace the capacitors, even when they show no signs of failure, you're heading towards imminent disaster and you must be stupid not to follow the advice of the "experts".
 
vwestlife said:
It seems that a generation of people latched onto that nugget of wisdom and now assume that 1.) it applies to all problems with all kinds of older electronics, and 2.) that if you don't replace the capacitors, even when they show no signs of failure, you're heading towards imminent disaster and you must be stupid not to follow the advice of the "experts".
Click to expand...
Ya', even some of those people you would think know better than that... don't.
 
Electrolytics that are leaking, need to be replaced. There was a period when elecrolytics were being made with a stolen formula that was wrong. Most of these caps have long since failed.
In old tube radios, the cardboard electrolytics are almost 100% bad. What were called BumbleBee caps were almost 100% bad( I've never seen one that isn't leaky ). Electrolytics in flat screen displays and TV are a constant failure point.
RIFA caps made in the plastic cases are notorious for failing.
Still, I believe one should trouble shoot the problem. Willy nilly replacing capacitor, especially by someone that isn't experienced in electronic repair causes a lot of new failures. A machine with two failures is a lot harder to fix than one with only one.
Capacitor replacing is use as an excuse to not learn how to trouble shoot. Yes, it does take some learning but then why bother making a problem worse. I helped fix a Altair of another person ( who's name is is not relevant to this post ). When he'd got it, it was said that it was working once and that it had failed for some reason. It did have the typical broken wires to the display board but it could never have worked. A simple ohm meter check of the mother board would have shown about 7 solder bridges. This machine never worked.
If I'd just replaced all the capacitors, I'd still have a non-working machine.
The little blue tantalums tend to pop every now an then. I wouldn't replace them all for the few that I see go.
Dwight
 
It does seem to be an excuse to not learn proper troubleshooting techniques, especially on older "magic" systems like S-100.
 
I agree with everything Dwight says in post 5.

I think the point is that every repair on any vintage electronics should be a targeted repair. Which means, for the most part, unless there is physical damage (such as cap leakage, overheated parts etc that gives the game away) the fault should be assessed where possible with the aid of the meters & scope and the schematic.

Only when there is adequate suspicion that a component is defective should it be removed from the pcb and replaced. A bulk replacement of components, like caps, is not logical or necessary and in less skilled hands runs the risk of introducing faults or pcb damage. It is good to keep vintage pcb's as original as possible and free from physical damage. I'm nutty enough to replace TTL IC's with ones of similar date codes to try to keep originality.

It can be surprising sometimes how good vintage electrolytic capacitors can be, especially if the item has low hours that is. One example is an IBM5155 power supply which I think was probably close to NOS. Not a single electrolytic in it is defective in any way. So it would have been a really bad idea to bulk re-cap it and the electrolytic capacitors in it may well be better quality than many we are seeing today.

The only time I break this targeted repair notion is when I see surface mount electrolytics in typically 90's vintage gear, like the logic boards on my 2465B scopes. I replace those on sight as the leakage is very destructive to the pcbs, and has already destroyed a good number of the A5 logic boards in these scopes. I can barely believe these capacitors are still popular. The A5 boards fitted with radial electrolytics, or tants, never have any issues.

The leaked electrolyte destroys tracks & components is a zone that extends far from the leakage:

http://worldphaco.com/uploads/TEKTRONIX_2465b_OSCILLOSCOPE_A5_BOARD_REPAIR.pdf

Also, if you see a pcb with an array of capacitors of some brand and age of electrolytic cap and even just one has leaked electrolyte that means the others probably will too in the near future, so in that case replace them all is a wise move. Dome topped dried out caps reading high ESR and low capacity, especially near heat sinks etc should always be replaced. In any case, it is a judgement call.
 
Experience is the key, I recently got given a couple of XT motherboards that somebody had tried to repair, They had removed all but 3 caps on 1 board and every cap on the other, Of the 3 caps left on 1 board 1 of them was shorted, The other board i found the BIOS rom was duff, I never repaired them as too much damage was done in getting the caps out but at least i got 2 good full sets of memory chips and other IC's.
 
If the machine was from the era of bad caps and you can see bulging or leaking capacitors then I replace all the caps around the CPU and any away from it that are leaking. Generally it is only the larger ones are get heated up from the CPU fan that also control the CPU power that have problems. G5 iMacs are one where I just do a recap of the board and also check the PC caps.

On old 68K macs that leak I replace all the SMT Aluminum electrolytics but leave the older style alone since they rarely go bad.

Tantalum capacitors that short tend to blow up so that are easy to diagnose.

I do so people who don't have a clue about computers wanting to recap a machine because it doesn't work, same with video cards.
 
The thing is failing capacitors, especially power related electrolytic - not so much tantalums, can cause all kinds of wacky problems.

I just the other day figured out why after all this time my floppy drives were giving me random read errors - it was my video card! A power related electrolytic capacitor is failing. The cap was getting hot, and last month or so is also started creating video interference I could change by spraying compressed air on it.

I also have a CRT TV set with a failing capacitor. When it is cold the video hight is too tall. Gets about right when after it runs for a while. Narrowed down the capacitor by spraying compressed air on it (height immediately jumped up). Haven't replace that yet.

I prefer "if it isn't broken, don't fix it" but I certainly can understand why people want to go through and preemptively replace them. Failing capacitors can be the source of all kinds of #$#$^$#^%$# headaches.
 
Do look carefully at the signal of a AC driven supply's filter capacitor. I recently was looking at would normally have been thought to be a failing filter capacitor. The voltage was dipping below where the regulator could handle it and causing erratic execution failures. A careful look at the signals showed that the peak were only 60 Hz. It was missing 1/2 the signal. It was an open in the bridge rectifier. Replacing that had plenty of margin for the regulators.
When looking at switching supply AC side, do note that 115V input supplies are usually voltage doublers while 220 are fullwave. The capacitors for 115V need to be in good shape to handle the higher charging currents.
Dwight
 
I'll just leave this here since both the incident and this thread are recent: Today I decided to spend some time on a multi I/O ISA card that 2 out of 3 times makes the BIOS complain about FDC + HDD controller failure (and of course no drives get recognized). By spending time I mean trying different drives on the card and the card itself on different motherboards. No luck, there was no logic or pattern. So just before tossing the card, because I'm not able to troubleshoot any further that that, I decided to replace all the electrolytic capacitors since they were only 4 and I had the soldering equipment ready to go from a previous job. Guess what... For maybe 100 times the card worked flawlessly after that.
So yeah, there are people like me who lack the knowledge and the equipment to narrow down the cause of a problem, plus this approach has worked many times in the past. Of course certain experience is necessary to justify such an action, putting the blame for everything on capacitors won't work. For example (truly) inconsistent behavior makes them a good candidate.
 
For things like CRT monitors, doesn't it make sense to buy a cap kit and replace them all while you're in there?
 
offensive_Jerk said:
For things like CRT monitors, doesn't it make sense to buy a cap kit and replace them all while you're in there?
Click to expand...

Yes and no. If it's not a monitor known to have cap issues, it's probably fine. Many old monitors do use a bipolar electrolytic which should IMO always be replaced, they don't survive well and they can take out part of the monitor circuit if they die. Aside from bipolar caps, I've recapped very few of the CRT monitors I've got, and most of them are from the 70s or early 80s (I don't typically hang on to VGA CRTs and newer).
 
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