Reed, thank you for the note about the switch on top of the board. I will check it out. Power supplies are OK and all voltages present. I read in the service manual about the "service ROM" and wondered whether that would still be available. I will bear you in mind should I need it.
Tom, thank you for the description of the error in the troubleshooting of the analog section. Will be carrying out that procedure soon so will bear that in mind.
Daveolla, thank you for the description of the files. I contacted Bruce and he has granted me access to the server. The files are now hosted on ftps and you have to e-mail Bruce for the access details. I did find the 468.zip file but not the bigger Tek468.zip. I did find a PDF of the adapter pinout in the files section on the TekScopes group.
A couple of tests for next time you are looking at the scope:
Check that RST7.5 is 50kHz not 500kHz. 500kHz would indicate that U440 is dead and would probably saturate the processor with interrupts.
Sorry, my mistake. Its at 500Hz which is as per point 5 in the test procedure, not kHz.
Check that pin 14 of U472 is also high so that we are not looking at a failed U472
Yes, pin 14 (gate output) is high, hence RST7.5 is high. Pin 13 (gate input) is at about 1.5V. Grounding either makes no difference. G1 (P1) and G2 (P19) are low.
Measure S0 and S1 (pins 29 and 33), that might show that the CPU had executed a HALT instruction and had at least done something after Reset.
S0 and S1 are both LOW which would seem to indicate a halted state. I tried monitoring both during reset/power up thinking that there should be some activity, particularly on S1 as the CPU boots and attempts to read the ROM but nothing happened - it just stayed low.
