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Old 16th Oct 2020, 1:22 pm   #4
ColinTheAmpMan1's Avatar
Join Date: Jan 2012
Location: Wimbledon, London, UK.
Posts: 1,362
Default Re: Tektronix 7623A poser

Yes, that fuse keeps blowing, which is what has suggested that Q1195 or some associated components (Q1190, C1198, L1198) may be at fault. This advice came from someone on Tekscopes, but they have all gone a bit quiet at the moment.

The low-voltage values are all OK, but the HV at -1475 V is absent (zero if I remember, but I can't power it up in its present state).

Another anomaly is that the voltage at the "collector" test-point on the storage board is -1.4 V, when it should be +150 V. This problem initially started out as an inability to use any storage mode, but has now turned out to be a complete loss of the beam. I have a transistor checker and was intending to check Q1195 without dismantling too much, but that looks like a dashed hope. I can see Q1195 on the HV cover, but I can't see the P1196 connector - I think it is in the HV box. I have purchased four 2N3055H power-transistors (which I think are the correct hometaxial types) from Farnell, as I have pretty-much convinced myself that this is where the fault of the lack of -1475 V comes from, if not also the inability to store anything.

Thanks for the disassembly info, the Service Manual is woefully vague about it.

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