Q840av capacitors

[beachycove]

Well, as my 840av would not start up today, I took it apart (as one does - try that on an iMac isight like I'm on now!), only to discover a case of the dreaded capacitor leakage situation. I had hoped that Quadra-era machines were still a little way off from this well-known failure on earlier machines (it's hard to find an SE/30 without it, for instance), but evidently time and tide wait for neither man nor machine. Presumably this fate soon must await the rest of my Quadras, and then progressively, my PPCs. Ho hum.

Let's see: 2008-1993=15 years, and then the logic board needs rehabilitation on a vintage Mac. Is that about the going rate? (This leads me to think: when it happens to my iMac, it's toast, because there's no way it will go back together if I have to take it apart multiple times come 2019 or so.)

The 840av logic board is having a soak in the sink overnight, and will be dried out over the coming few days for a quick and hopefully easy, if temporary, fix.

 

[equill]

Call me a Jeremiah if you will, but washing off capacitor goo is not a fix, even temporarily. It's a respite, at best. A fix is capacitor replacement.

I'd be interested to hear from fellow-enlisted about their experiences with MDD power supplies. I've just replaced the dead PSUs in a 1GHz DP and a 1.25GHz with NOS original 400W supplies, transferring the fans from the 360W PSUs in the process. In my wide-ranging sample of two, the main 390µF filter capacitors were bulging at the top in the dead PSUs, and both blew replacement 8A 250V fuses instantly on power-up.

Plus ça change ...?

de

 

[Unknown_K]

I noticed on my dead PC PS units that the caps were bulging too, it is cheaper just to buy another PS then to source out all the caps and fix it (asuming nothing else blew up in the process).

My 2nd 840av is dead from bad caps (turns on but no chime), just waiting untill I feel like working on it. If left leaking long enough capacitor goo might eat into the electronics killing it (I removed the board and washed it). From my recolection there are 13 aluminum capacitors, 2 of which at 10uf 16v and the rest are 47uf 16v. The Tantalum SMT ones probably do not need replaced.

 

[beachycove]

To equill:

Yes, but the definitive step (capacitor replacement) can be taken later. I will, for instance, need to source some tantalium caps, and that, in these parts, can take some doing. I also fear the doing of it, as I have no training. The proximate end is in any case to ensure that the goo has gone, and to determine that the ps, etc. are still in good order by successfully firing up.

To unknown-k:

In this connection, I note (following overnight soaking and morning rinsing, with some light toothbrush treatment in the afflicted area for good measure) that there is remaining discolouration on the copper traces near the main power supply connector on the top of the logic board. There was capacitor residue in this area – I remember this distinctly, as this was the first of it that was spotted on the board yesterday, which, as you might imagine from Psych. 101 and the school of life alike, elicited an immediate linguistic response from and on the subject.

Would it be good practice to go over this area of discolouration with a circuit pen, or is the trace not strictly on the surface, but buried underneath a minute insulating layer of je ne sais quoi?

Forgive my ignorance; I am electronically-challenged. We weren't taught this subject at school in my day, and I later went into the humanities.

 

[Unknown_K]

Washing probably removed most of the capacitor goo (water based I would think), if not some alcohol and a q-tip will get rid of what is left (not rubbing alcohol since that is only 70% alcohol and some other junk).

Discoloration while bad is not the end of the world as long as the trace is still intact and not etched too badly where it will become a hot spot and fail. Even then you might be able to bridge a broken trace with a wire jumper. Generally I keep a multi meter around to check if there is a broken trace.

 

[equill]

The verdigris-like green deposit induced by the (barely) alkaline electrolyte of electrolytic caps does indeed need to be removed so that you can be sure that no traces have been severed during its formation. Had that been so your linguistic response might well have included Quel dommage, or something even more piquant. The possibility that traces have become friable after etching is a good reason to rely on solution of the deposits rather than friction (with, eg a toothbrush). Board-washing and recovery has already been done to death in these forums, so there is no lack of guidance available for you.

Do, however, remember when you psych. yourself up to cap. replacement, that our very own trag makes tantalum cap. sets available to members of this Army at very reasonable cost. Quote the numbers (quantity, not type) and capacitances (in µF) to him and he will most probably be able to cook you up a mess to suit.

As Unknown_K points out, even broken traces can be repaired by bridging with a single strand (for signal-traces) from stranded cable, or a heavier-gauge strand or wire for supply traces.

de

 

[equill]

... it is cheaper just to buy another PS then to source out all the caps and fix it ...

In the case of the solitary main cap. in a PSU such as that from an MDD, that is probably less true. If the capacitor's demise in each case also took with it the FETs, that might be a different story in terms of cost. 360W PSUs go variously from USD150 used to USD300 new before postage, from sellers in Hong Kong to USA. I was fortunate to stumble on locally-available new 400W PSUs for AUD175, with Shanks' pony as the only delivery cost. I am aware of a local repairer of MDD PSUs, but the cost and feasibility of repair I have not yet explored. Not all PSUs, I hear, can be repaired.

... Forgive my ignorance; I am electronically-challenged ...

No forgiveness is necessary. We'd probably be -challenged in your corner of Humanities.

de

 

[Unknown_K]

I think I snagged a MDD PS for $60 plus $15 shipping (LEM swap) a year ago for a local guy, they are more on ebay.

A IIgs I snagged last year worked for about 30 minutes and blew its PS, was cheaper to get a new one then bother fixing it ($5 plus shipping or something like that). I still have the dead one because I figured someday I might want to repair it to see what was involved.

As the 68K's get older you will find that the cost of parts will get high enough to justify repairs (superdrives anyone?). G4 machines are still in use so some people do repair/replace the blown PS in them, but I have seen dozens that blow the PS and are just parted out not deemed worth repairing.

 

[Mike Richardson]

As the 68K's get older you will find that the cost of parts will get high enough to justify repairs (superdrives anyone?). G4 machines are still in use so some people do repair/replace the blown PS in them, but I have seen dozens that blow the PS and are just parted out not deemed worth repairing.

We usually part any G3s or older G4s that have a big problem. I can fix 3-4 iMacs by parting out one iMac with a bad power supply.

 

[beachycove]

Well, washing restored partial functionality. A Jackhammer SCSI card is still not recognized, but at least it boots. The capacitors will undoubtedly have to be replaced.

 

[ianj]

I've had this problem with two consecutive 840AV logic boards - no goo, but clear signs of dying capacitors. I don't know if I'd do the job right, so one of my logic boards is currently sitting in the office of a friend of a friend who does electronics work, waiting to be addressed...

 

[tomlee59]

Call me a Jeremiah if you will, but washing off capacitor goo is not a fix, even temporarily. It's a respite, at best. A fix is capacitor replacement.
I'd be interested to hear from fellow-enlisted about their experiences with MDD power supplies. I've just replaced the dead PSUs in a 1GHz DP and a 1.25GHz with NOS original 400W supplies, transferring the fans from the 360W PSUs in the process. In my wide-ranging sample of two, the main 390µF filter capacitors were bulging at the top in the dead PSUs, and both blew replacement 8A 250V fuses instantly on power-up.

Plus ça change ...?

de

Your post got me off my brains long enough to take a look at my two dead MDDs. Bulging caps are evident. Seems to be a common problem, based on our extensive sampling.

 

[trag]

Do, however, remember when you psych. yourself up to cap. replacement, that our very own trag makes tantalum cap. sets available to members of this Army at very reasonable cost. Quote the numbers (quantity, not type) and capacitances (in µF) to him and he will most probably be able to cook you up a mess to suit.

I have 47 uF and 10 uF tantalums available. The details are in my post over in Trading Post. If you don't have time to do the work yourself, then see Mike Richardson's service, also in a posting in the Trading Post forum.

One of these days I must make time to do all my own boards...

 

[Unknown_K]

Do you have any of the 10 uf OEM style aluminum electrolytic surface mounts traq?

 

[trag]

Do you have any of the 10 uf OEM style aluminum electrolytic surface mounts traq?

For practicle purposes, no, I do not. I have a handful--maybe 10 or 20, that I ordered for my own use back before I became aware of tantalums. I'll probably never use them now, so I guess if you have some particular interest, I wouldn't mind selling them to you. They're probably going on ten years old though.

Email me if you want them for some reason: trag@io.com.

If it was just curiosity, that's fine too.

 

[Unknown_K]

I found the correct aluminum ones in Canada and ordered them, they will be here sooner or later.

 

[samy4movies]

Does anyone can tell me if is there any hope to fix the power supply for a Mirrored Door G4?

The prices at ebay are around US 150 up to $200.

Does anyone knows a repairshop for this PS?

Should I get rid of it? sale it for parts?

Thanks for those that could provide any advise?