My //c internal voltage converter repair

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Joined: May 8 2015 - 17:29
My //c internal voltage converter repair

I recently came into a couple //c computers via a local Craigslist deal. Expectations were low but one was a nice ROM 3 with the memory expansion slot!
The second had some problems, starting with not powering up. Via a swap I was quickly able to nail that down to the internal power converter, as it's external power supply was just fine. This second unit is the original //c design, before Apple fixed the serial port issue, as is evident when I compare boards with my other //cs. After a ROM upgrade so I can run the internal memory tests, then identifying, de-soldering, and socketing in 4 RAM chips, the thing was working like a champ.

For the motherboard repairs there is so much great information out there. For the power supplies I wasn't finding much information for the //c line, so knew I had to dig into this one alone. Looking for any experiences on a "minimal fix" yielded nothing. Failed electrolytic capacitors is first on the list, but on close inspection of the board there just wasn't any of the usual telltale signs. No detectable swelling, no leakage, no "dirty" areas, etc. Knowing that best practice is to replace them all anyhow, I did a inventory and placed my order.

With the "minimal fix" still in mind, I decided to be methodical on my recap job and go for likely suspects and check the repair at each stage. I identified my first suspects, prioritized them, and planned to desolder, test the capacitor with my multimeter, and if good go for the next one. My second suspect tested bad, so at that point I soldered in my two new caps and BINGO!

So, I'm posting here for what it's worth. The minimal fix for me ended being replacing two capacitors, C16 and C17. C16 is the one I had identified as "bad" via my multimeter test. The only thing to caution is the need for a hot iron and patience as you desolder to two devices. Based on where they sit on the circuit board the heat dissipation is something I was fighting against, causing me to curse at my brand new soldering iron Smile

With the //c now working, I am debating whether to replace the remaining caps. I know I should, but i hate desoldering .... lol

Here's my parts list for the intrepid with a bad voltage converter and who wish to follow in my footsteps. If you've got one you have messed with because you also hate desoldering, try the simpler two capacitor replacement a try and see how it flies. Total cost, $1.05 for the 2.

If pictures are helpful for anyone, I did snap a couple of the board and one with the caps removed before soldering in new. I would have posted them now, but was too lazy to go get my camera (do you sense a trend here). But seriously, if there is interest, let me know.

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IIc Internal Voltage Converter Electrolytic Capacitor List </p>
<p>Cap Voltage Capacitance Temp<br />
----------------------------------<br />
C3 	35v 	3300uf 		85C<br />
C17 10v 	1000uf 		85C<br />
C10 10v 	1000uf 		85C<br />
C9 	16v 	330uf 		105C<br />
C11 16v 	330uf 		85C<br />
C16 16v 	220uf 		85C<br />
C18 35v 	33uf 		85C<br />
C6 	50v 	1uf 		85C<br />
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Mouser #:	647-TVX1V332MCD<br />
Desc.:	Aluminum Electrolytic Capacitors - Leaded35volts 3300uF 16x41.5 20%<br />
<p>Mouser #:	647-UVR1C102MPD<br />
Desc.:	Aluminum Electrolytic Capacitors - Leaded16volts 1000uF<br />
<p>Mouser #:	647-UPM1C331MPD6TD<br />
Desc.:	Aluminum Electrolytic Capacitors - Leaded330UF 16V 105c<br />
<p>Mouser #:	647-UVP1C221MPD<br />
Desc.:	Aluminum Electrolytic Capacitors - Leaded16volts 220uF Radial Audio<br />
<p>Mouser #:	647-UVR1V330MDD<br />
Desc.:	Aluminum Electrolytic Capacitors - Leaded35volts 33uF 5x11 20% 2LS<br />
<p>Mouser #:	647-UVR1H010MDD<br />
Desc.:	Aluminum Electrolytic Capacitors - Leaded50volts 1uF 5x11 20% 2LS<br />
$0.23<br />
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