Alex, adding to what Robert has said, Charles at Maccaps.com doesn't use
bulk-buy low quality capacitors which can also give you problems due to poor
quality control during manufacturing.
At Maccaps, they use branded capacitors, with specific values to cover or
exceed the original specification of the PSU. The original caps may be rated to
85 degress centigrade but modern caps are rated to 105 degrees so will last
longer.
That's essentially what has happened inside your PSU. It heats up and causes
the semi-liquid electrolyte to eventually become dried up. This changes the
values of the capacitors so that they no longer function as required and your
PSU stops working.
Sometimes, as the capacitors are being heated, they boil what little is left of
the electrolyte and you hear a pop. a little bit of smoke may escape from the
case and this is also the remains of the electrolyte.
As well as meeting the voltage and capacitance values, another important factor
in PSUs is ESR and leakage - that's electrical leakage. Capacitors can be
likened to batteries in that they store a charge and release it at a set rate
in a set time. If you have batteries stored in a cabinet for years and they are
three years past their USE BY date, chances are the electrical charge in the
battery has dropped below the required level and you will find they no longer
work or they only work for a short period of time. A PSU needs to release the
charge from the capacitor at a certain rate to ensure a smooth voltage output
to power the logic circuits and the power circuits.
The other problem is that over time, the electrolyte in the PSU will leak as it
heats up and it will leak out of the aluminum can. The electrolyte is corrosive
and will eventually damage thin circuit tracks on the logic board. It will also
cause a short circuit between tracks as it is partially conductive. This leads
to other problems.
As part of the capacitor replacement service, maccaps.com clean the boards
thoroughly to remove any contaminants such as old electrolyte to ensure that
the board works correctly.
Here is a link (it's for a Dell PSU but it will give you an idea about what is
going on): Dell Inspiron 530 Power Supply Repair Capacitors
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Dell Inspiron 530 Power Supply Repair Capacitors
quick and dirty partial recap | |
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hope this helps,
Keith
From: Robert Hesson <[email protected]>
To: [email protected]
Sent: Monday, 27 February 2017, 13:55
Subject: Re: PSU failure on 8100
What you are describing is capacitors detonating which is common for old PSU's
and surprisingly cheap to fix. I would look up maccaps.com (I've used him-
great work from a great knowledgeable guy) or if you have a local electronics
guy he can take care of it too. I recently had to have a power supply for a old
PC recapped that ran a proprietary water jet machine and it cost me $15. (A Mac
will cost you more...) Not bad to get a $250,000 machine back up and running.
Also, if the caps in the PSU are going, the caps on the logic board are going
too. Mac caps did my centris pretty inexpensively and it works great (after my
power supply was recapped..)
I learned video editing on an 8100/80 back in the day so that machine holds a
special place in memory for me. Good luck.
Sent from my iPhone
On Feb 27, 2017, at 5:31 AM, 'Keith Jamison' via Vintage Macs
<[email protected]> wrote:
Alex,
It's more likely to be failed electrolytic capacitors - it's a common problem
with old machines. If you are in the United States, head over to Maccaps.com
and Charles Phillips can repair it for you.
Even with my background in electronic engineering, the first time I opened a
faulty Mac, replaced the capacitors and heard it chime into life, I was
speechless.
Charles is an expert when it comes to capacitors and repair work.
Of course, if you happen to live elsewhere, a local TV repair shop or
electronics repair shop could do the same job for you but they might charge you
more.
It might be less expensive to get another PSU off eBay but then you canot be
sure that it will work flawlessly if the capacitors have not been replaced. It
is only a matter of time before they fail.
At least if you get the original PSU repaired, you know that it will fit into
the case again.
All the best,
Keith
From: Wesley Furr <[email protected]>
To: [email protected]
Sent: Monday, 27 February 2017, 1:44
Subject: RE: PSU failure on 8100
They're all different, but shouldn't be too difficult. May be able to see what
is going on without totally tearing it apart. Wesley
From: [email protected] [mailto:[email protected]] On
Behalf Of Alexander
Sent: Sunday, February 26, 2017 8:28 PM
To: [email protected]
Subject: Re: PSU failure on 8100
Thanks, that's an option as well, although I don't have too much experience
with opening PSUs
I will completely remove it and open it, I'll share a pic here If you guys want.
On Mon, Feb 27, 2017 at 3:26 AM, Wesley Furr <[email protected]> wrote:
Don't know much about that series of Mac...but in looking online, doesn't
look like it is a stock standard type (AT/ATX/etc) power supply. May be able
to re-wire an ATX power supply, though the power-on part might be a challenge.
Probably worth pulling the cover off and having a look inside - could just be a
blown capacitor or something easily replaced. Wesley
From: [email protected] [mailto:vintage-macs@ googlegroups.com]
On Behalf Of Alex Ander
Sent: Sunday, February 26, 2017 7:55 PM
To: Vintage Macs
Subject: PSU failure on 8100
So I just plugged in a 8100 that is 20 years old. POP goes the PSU. A few
bang noises very very little smoke.
I guess repairing these isn't worth it.
If I want to get a replacement from a PC, what would I be looking for?
The PSU in the machine is a Delta Electronics DPS-225AB
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