# 1231c-8601 rebuild question



## Kerensky (Jul 8, 2011)

hi all 
as some of you may or may not know i am an ev noob attempting to rebuild a curtis 1231c-8601 which made the poporn sounds and the magic smoke..... we managed to find replacemet diodes and mosfets, a further problem on the logic board has come up. what follows is a direct copy/paste from my bench tech friend

I looked at the main module and it looks ok.
The small pcb on the side of the module is probably
the problem. Look on your sites for these two questions.
#1 On the heat sink all the semiconductors mount directly to the
heat sink but one semiconductor and that semiconductor has a
isolator that keeps it isolated from the heat sink. The orginal device
was destroyed and I could not get a part number off of it. Try to find
the part number of that one device.
#2 Check to see what problems others have had with that logic board
which is mounted on the side of the heat sink.
Let me know what you find out.

as always thank you for your valuable time and any help you can provide


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## Weisheimer (May 11, 2009)

I think that the isolated transistor is the power stage of the low voltage regulator.
It is a NPN 250v transistor in a TO-220 case as I recall.

The 1221c isn't quite the same as the 1231, but it is similar.
See Otmar's schematic at:

http://www.cafeelectric.com/curtis/curtisschematic.pdf

There is also a manual for the 1221c that has a bit of a theory guide at:

http://www.cafeelectric.com/curtis/Curtis_manual.pdf

The issue of what else happens to the logic board is quite broad if that LV regulator let go and let full B+ onto the logic board...

Still, I've seen them with 1/2 inch holes burned through the logic board that were repaired and continue to work for years.

Cheers
Mark


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## Kerensky (Jul 8, 2011)

but the 1231 runs on full b+ normally doesnt it ?
.... thanks the diagrams do look beautifull. i hope they apply to the 1231 and not just the 1221.


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## Kerensky (Jul 8, 2011)

hello again all.... i have new info and im digging for more advice......i am inserting a pic of the logic board from my curtis..... we found a resistor ( i believe r21) with some signs of dammage and if i understand what im looking at its directly in series with pin 1 of the mosfet driver........ 










Question 1..... has anyone seen this failure before ?
Question 2..... what caused the failure in your instance?
Question 3.....how much of this logic board u guys/gals think im gonna have to replace?

any and all advice is aprecieated and taken to heart

P.S. Weisheimer thanks for the links they helped more than i could have believed, please forgive my lack of faith.


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## Kerensky (Jul 8, 2011)

Just refreshing the page to bring to top. Still fishing for input


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