{"id":1524,"date":"2023-01-07T10:00:27","date_gmt":"2023-01-07T15:00:27","guid":{"rendered":"https:\/\/paulcarbone.com\/blog\/?p=1524"},"modified":"2023-06-04T10:16:36","modified_gmt":"2023-06-04T15:16:36","slug":"tektronix-564-continued-weirdness","status":"publish","type":"post","link":"https:\/\/paulcarbone.com\/blog\/tektronix-564-continued-weirdness\/","title":{"rendered":"Tektronix 564: Continued weirdness – SOLVED"},"content":{"rendered":"\n
\"\"<\/figure>\n\n\n\n

2 years ago<\/a>, I attempted to troubleshoot and repair an intensity modulation issue on my 564, but ended up giving up after a few unsuccessful attempts. I had replaced a few power supply caps, and all voltages & ripple were within spec. I thought maybe <\/em>it could be an issue with the CRT? Last month, a spare CRT popped up 30 miles away for $40, so I grabbed it. I made the swap, and the issue remained. <\/p>\n\n\n\n

I have since changed out the remainder of the electrolytic caps in all ‘low voltage’ supplies (all but the -12.2V – I don’t have a good way to mount new caps, and the ripple is really non-existent). I swapped the vertical and horizontal plugins, and never saw the issue, but I think this is a red herring, as when I put just the vertical plugin in the horizontal slot and feed it a 60Hz ramp, I do see the issue. I did this 2 years ago, and confirmed it today. The other thing I did to eliminate my suspicion of the horizontal plugin was to pull the transistor that drives the intensifying signal, Q294. When I pulled it, the issue diminished a little bit, but was still present. <\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

Other things that didn’t work:<\/p>\n\n\n\n

Disconnecting the intensifying pulse input – had to leave R838 & R839 connected, otherwise the beam intensity was unstable.<\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n


Maybe there was some heater to cathode leakage in the HV regulator tube? I swapped it out with a 12AU7 (similar pin out, close enough performance), the same issue occurred.<\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

The ripple of on the primary of the HV transformer seems negligible, and in line with what I’d expect on a simple unregulated supply. Allowable ripple isn’t listed on the manual like it is for the other rails.<\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

May be on to something: I’m seeing at least 5V of ripple on the grid of V800. <\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

I thought the ripple on the 300V supply was in spec, but I just noticed a filter cap I missed on the other side of the regulator, that’s tucked away in the back of the scope. No change after swapping out that cap, but I think we’re getting closer. When I see problem, I’m also seeing ripple measurements jumping around. When the trace is solid, the ripple is rock steady at less than 5mV. <\/p>\n\n\n\n

Things to suspect next:<\/p>\n\n\n\n