Apple IIc TDK internal power converter schematics / info

GondolinOnMyMind

New Tinkerer
Mar 14, 2023
29
9
3
All,

I managed to de-repair the internal power converter. There are two possible issues, at least. As I had the computer open, I decided to replace the capacitors, as a precaution. I did replace the capacitors in two batches (due to some missing cap's) . On the first run I noticed that one capacitor, C2, is installed wrong way, as opposite what the silk screen says. Also there was and is a short piece of wire connecting two vias underside and a trace seems to be cut. The converter did work before i replaced the first batch, including this C2, and it also worked after replaces. So I guess the silk screen is erratic.

I did not notice any other capacitor to be installed wrong way related to the silk screen, but I can't be certain.

After the rest of the capacitors arrived I replaced those too. Then I did put the board back in the casing and tried to get the latch (?) to hold the transistor against the casing correctly in place. But I guess I failed with that, as the converter does not produce any voltage outwards anymore. I checked the transistor (C3568), and it seems to be shorted. This may have caused some other damage too.


Now the questions are

* does anybody have schematics of this converter? Details are below.

* could somebody confirm that C2 is only capacitor to be installed wrong way and the trace beneath is cut

* what voltages should be seen on pins of the transistor?


On the board itself is text PCU-266E. On the metal casing are texts TDK 699-0230, CE-045 8511 and serial number.

And yes, I managed to pull one of the pads of C2, but corrected it with a bit of solder bridge.

Please see pictures below. Unfortunately the trace cut is just below the red arrow, but somehow visible.


powerconverter-C2-underneath.jpeg
TDK-powerconverter-PCU266E.jpg
powerconverter-C2.jpg
 

piom

New Tinkerer
Oct 23, 2025
5
2
3
Well it is probably to far... and you have solution for your problem.
Any way... I have also done recapping but stick to polymer-electrolitic than pure electrolytic, as polymer-electrolitic are stable and do not use fluids, and should last longer. I have been inspiring myself with this article:
Also doing based on that article my Commodore recap.

But back to Apple IIc, at the beginning I have replaced MB caps C57, C44, C43... leaving C60 as it prevents oscillation of IC 7905... and this gives no problems.
Then I have replaced three caps in disk station the connection board, also no issue.... then I have changed caps marked green and yellow on the chart:
Apple2cCaps.png

well.... it works... but this power converter generates now high pitch noise very loud. I have tried to recap back each capacitor to old one without any change/improvement. yellow capacitor had some legs problem first but corrected. The sound is from transformer, but it is not vibrating. The blue caps on the chart are new electrolytic, as I do not found polymeric for them, also for others (well for others, they came... but required special care - backing... what!?).

My PSU board does not have your broken path (EU 230V 50Hz version), and all caps were mounted in directions as dictated on the board itself:

20251023_183857.jpg

the full layout:
20251023_183735.jpg

Board with replaced caps:
20251023_183934.jpg

I have checked offline the 3568, looks fine:
20251023_184432.jpg

20251023_184450.jpg
 

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piom

New Tinkerer
Oct 23, 2025
5
2
3
The difference I see is SHARP IR9494 in mine vs NEC uPC494C in yours - if it has been replaced then compare pinout of yours in datasheet if is the same with SHARP's.
 

GondolinOnMyMind

New Tinkerer
Mar 14, 2023
29
9
3
in my both(1 TDK built converters I do have the same Sony uPC494C. They seem to be original and there is no visible marks of replacing the chip.

Much later after starting this thread I began to suspect the big transformer (marked "86") is defective. It has input via the capacitors, but none of the other pins have no voltage at all. I have not found any info of this transformer, so I'm kinda halted resolving this issue.

(1 Yes, I had to buy another converter for the same Iic :-(
 

piom

New Tinkerer
Oct 23, 2025
5
2
3
TDK-Apple2c-A.png

I have traced the schematics.
TDK-Apple2c-B.png

If you want me to measure something, please provide the attaching points and conditions (powered/offline).

EDIT: Updated coloring by electric potential, schema updated with grounding.
 
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piom

New Tinkerer
Oct 23, 2025
5
2
3
If you suspect the transformer, then desolder it and do measurements: continuity, resistance...
Please, if you could note which pins are connected internally, so I could update the schema.
 
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piom

New Tinkerer
Oct 23, 2025
5
2
3
If I may ask how did you create both the schematics and trace backgrounds (on both sides)?
I have taken the picture of the board, converted to black and white in Gimp. Then traced to vector in Inkscape, then separated paths, applied colors to each "island", mirrored, reduced opacity, manually placed components.
Then in another layer where the components were placed I have made connections between components and hidden the original traces, then moving components around to make it more clear, but my friend at work has advised me to remove all wires that are grounded (replacing by GND symbol; he found some missing jumper on my scheme) and I should then move input voltage to left and outputs to right, higher potential lines on top and ground to the bottom, separating "hot" and "cold" part of transformer T1. I have made it because the friend said that he will advice me what should potentially be tuned to change resonances, but he need the schema to analyze. I have gotten a few clues, now... but also it will take me a little to gather components for tests.
 
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