Re: CL: Lot of 5 Tek 453's

 

It's been a while and I didn't take notes but I remember that I could see that the phase info (U1902 PFC, pin 23) was dead (steady state). Of course, I first looked at TC1 (pin 1) and VCO (pin 26) and found both alive and well, so the X-tal oscillator and U1904D (level shifter) couldn't be the problem. Partly just for confirmation of my conclusion, I decided to just cut pin 23 (PFC) and put in one gate of a socketed 'LS86 between pins 1, 26 (inputs), and 23 (output). Works a treat! As said, a bit rough but accurate and stable. I think that i didn't even put in a pull-up resistor at pin 23, which strictly speaking shouldn't be necessary but may improve shape and level. Of course, a bit of HF jitter does no harm in this application and is actually inserted through pin 22 (Noise).

Raymond

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