Hello, it's me again with a damaged Philips T&M Instrument
This time it is my PM6654C, which I had equipped with a OCXO (Morion MV103) just last week.
Upon startup all digits just show "0" and all the LED in the buttons stay off, but when I perform the manual reset with the reset-button on the front AND then turn the knob that controls the measurement-time, a random number of LEDs come on and I can hear reed relay click.
The knob for the measurement-time controls a 555-Chip that puts out short pulses, which directly feed into the D8741 Slave-Processor that controls the display and keyboard. So I'm guessing that the fault is in that chip. I'm also suspecting the 8741, because about a month ago I repaired my PM5190 that also had a Microcontroller out of the MCS-48 family, which failed in a rather strange fashion.
Also the rising edge of the Clock is a bit slow and there's no flat top on the clock-signals to the Processors. I'm a bit suspicious about that, but I don't know if that's normal for Low Power-Schottky-Logic or not.
If it really is the 8741 Processor though, I have a bit of a problem: The processor has an internal ROM and although I was able to download the complete Firmware for this thing, I cannot program that particular chip because my Programmer is a TL866.
Is there a way to make the TL866 program a 8741, or any µController out of the MCS-48 Series?
Is there also another possible cause for this failure / has anyone dealt with a simliar problem before?
Btw. I have measured Voltages and they are all within spec, which are quite tolerant (11,4 to 12,6V on the +12V-Rail for example).