OK, this is really a question for anyone who has full refurbed a CPP-2 or might have one on a bench where they can measure some voltages. For the rest of you this is probably going to read like gobbledygook.
I have an old CPP-2 which is mostly working, except that the temperature display is '---'. (It was working until very recently).
Normally this would be a sign of a failed temperature probe but I don't believe it is in this case (I might be wrong!) as all the voltages seem to read within the specs on the schematic shown in the online service manual. The probe shows a resistance of about 800ohms at 15C.
The issue appears to be with IC45. I am getting around 100-150mV on the input to pin 11 which is within the 0-0.5V limits on the schematic, with pin 10 at 0. However the chip is putting out a signal of negative signal out of range.
The one weird thing on my board is that pins 8 and 9, the zero offset, which are both linked to V+ by identical resistors, are at 4.9V and 4.7V respectively, ie pin 8 appears to be shorted to V+. However there's no sign of a short on the board and all the resistances measure correctly.
So my questions to anyone who might be able to answer them...
-- what would be a sensible voltage across pins 10 and 11 of the IC? From the datasheet it looks like -99mV to 999mV.
-- what should pins 8 and 9 be reading at?
-- what would be a sensible resistance for the temp. probe?
My working assumption is that IC45 has failed but I'm no electrical engineer. I attach a schematic with my measured voltages. All help gratefully received, and no, I'm not in the market for a CPP-3, thanks.
I should add that the outputs appear to be working fine, as do the LEDs.
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