Paul Barteldt

Hello everyone, I would like to tell you about the error.

The oscilloscope can be switched on, the fan is running and the 
Key lighting stays on permanently. On the A11 DRAM 
Processor/Display Board number 8 lights up on the segment display.

The device had a problem with all SMD capacitors. Partial are 
she expired. Then I replaced all the capacitors and the 
Circuit boards thoroughly cleaned.

Unfortunately, this action did not fix the error.

I then started troubleshooting using the service instructions.

Here are the links to it:

Volume 1:
https://w140.com/tekwiki/images/6/62/070-8312-01.pdf

Volume 2:
https://w140.com/tekwiki/images/4/48/070-8313-00.pdf

I carried out the diagnosis on Volume 1, page 187. The fan is running
and after approx 30 seconds the key illumination does NOT go out. Thereupon 
According to the instructions, I troubleshooted the processor/front panel 
procedure (Volume 1 page 195).

I checked all the required voltages on connector J2. The 
are all OK. The clock signal (3.125Mhz) is also present.

According to the instructions, the communication link is between the A11 
Display/processor board and the A12 front module faulty. The A12 
Front module is most likely defective and should be replaced 
become.

There are a lot of troubleshooting instructions described in volume 2 but I think 
Unfortunately not one that applies to me. I think there are missing too 
a few pages.

Nevertheless, I have part of the processor on the A12 board 
measured (Volume 2 page 218). Unfortunately the 3rd page is missing there.

I noticed that there was no 2Khz signal on pin 2 of the processor (U1). 
applied. This means there is no 1Khz square wave signal to set 
probe. The operating voltages according to the circuit diagram are all on 
processor on. The clock signal from the A11 board is also present.

Does anyone have an idea what this could be?

I wish everyone a merry Christmas!

Greetings from Germany
Paul