I have yet to check them out, but the waveforms I see are sufficiently identical to the ones in the manual, so I'm thinking they're ok.
From what I know of the circuit:
Inputs are conditioned, run through transistors, applied to a tunnel diode which produces very fast spikes, looks like per half cycle.
Those spikes go to a very specific, custom made ECL chip (no idea what's in it).? The output of that chip is translated from ECL to TTL, which then is fed to the counter chain.
There's a bias adjustment on the custom chip (this is for early serial numbers only).
Changing the bias adjustment goes from (I guess)
1) ignore everything
2) respond to inputs
3) oscillate and generate an output
4) likely ignore anything again
1, 3 and 4 work.
Since 3 generates outputs that are translated to TTL, I'm thinking that the circuitry *there* works.
The symptoms of mine are that it is completely dead.
Looking at the inputs to the custom chip, they seem to be correct, although Tek doesn't give me the exact waveform, but mentions what it ought to look like in the adjustment section.
So I'm considering that the major chip might be dead.? If it's not, then it's not properly adjusted.? No amount of misadjustment makes the counter work.
It's dead, Jim.
Harvey
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On 1/12/2022 9:02 PM, Mark Vincent wrote:
Barry,
I was incorrect about the 7D15 using 0367 types. They use 0402. They are the same transistor with a different number stamped on it. They are most likely leaky from C to E. The 0402 is only in a 7D15.
Mark
