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Old 20th Oct 2020, 4:51 pm   #18
ColinTheAmpMan1's Avatar
Join Date: Jan 2012
Location: Wimbledon, London, UK.
Posts: 1,354
Default Re: Tektronix 7623A poser

Originally Posted by tony brady View Post
Colin, did you see that C1193, C1198 & Q1195 all have a triangular symbol for ground? this goes back via pin 3 of the connector P1185, pin 3 of P1195 and pin 1 of P1180 to the power supply connector P870.

be careful that the connector P870 is correct because there is a mistake in the pdf of the manual that I Have where pins 1 & 2 both appear to be +15V unreg depending on which end you look. ( on diagram 7 pin 2 of P870 is +15V unreg whereas on diagram 8 pin 1 is shown as +15V unreg from the fuse). so check the orientation of P1180 and buzz the unreg +15V from the fuse to L1198 and the 0V from the psu to the triangle marked grounds on Q1195 etc
I have checked the continuity of these:

C1193, C1198 and Q1195 do indeed go back to the power-supply and not to an earth-point in the HV module.

I have checked that the +15V unregulated supply is continuous from F814, P1180 and P1185 on the X-axis board, through P1195 and the +15V end of (the O/C) L1198), so I am guessing that the A10 High Voltage board (and its connection to the +15V unregulated supply connections are fine.

My paper copy of the service manual looks to be accurate with regard to P870 and I have not disconnected it from the A11 regulator board, nor have I taken the LV power-supply out of the mainframe, though I will eventually have to when I replace fuse F814. I suspect that the problem is that you are reading the pin-numbers on the two-pin connector P1180 as GND is pin 1 (or index) and at the other end of the cable, the three-pin connector P870 has +15v on pin 3, GND on pin 2 and nothing on pin 1 (or index).

Hopefully, I will be able to fit the new capacitor and inductor and put the whole back together. I certainly hope it will then work, if I am lucky? (I usually seem to have poor luck these days).

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