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| Fool for the 8656A Sig Gen |
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| jrharley:
Of course! The crime is unfolding. ;) I'll be looking at what I've uncovered with respect to the schematic tonight, and sticking a meter or two across the pins of the board to see what more I can learn. Once it was free of its tethers, the A14 board was easy to remove. Photos attached. JRH |
| Tony_G:
Interesting - The caps have to be somewhere :) This is really turning into a mystery... The parts list for the A14 board shows the connectors being part of the board: And the caps themselves are listed as standalone parts: Coming back and looking at the schematic: It shows a 1000pF cap between the ground and J1 P15 & J2 P7 - The note says that the chassis ground is provided by the mechanical connection of the D-Type to the frame - Try measuring between those points to see what is there. My only other thought is that they are in the wiring harness somewhere so you might want to follow that and see what happens to it between A14 and A10. TonyG |
| Swainster:
Hi guys, I'm still following along. I definitely agree with the idea that the caps are inside the potted D-sub connector. BTW, I swapped the rear panel from my working 8656b to the non working one and it powered up without issue. Well except for the frequency being pretty far out and 3-6dB down from the front panel setting. So I guess the seller was on the level about it just missing its power transformer. From your pics, the mechanical arrangement of the rear panel of the 8656a is slightly different to the 8656b, but I seem to think that the overall power supply circuit is pretty similar. Would you like any points measured for comparison? |
| Tony_G:
--- Quote from: Swainster on January 27, 2023, 12:13:45 am ---I definitely agree with the idea that the caps are inside the potted D-sub connector. --- End quote --- I think you're absolutely right - I asked on another forum and that was the feedback. I'm also wondering about the rectifier diodes as a source for the ripple seeing that the caps are all good. TonyG |
| jrharley:
Wow, 'yall! Terrific feedback. Lot's to run down, so it's going to take a bit, but I really appreciate the input. :-+ Thanks for weighing in swainster, good to know I can reach out for a cross check on the power supply measurements. I've managed to test the A14 caps and they all read low. I thought it was interesting that the parts spec's said that they could be low by 20%, but not high at all. A couple are a bit too low, but otherwise this looks good to me. I couldn't help but then look to the hidden board A12. Looking at the schematic, these caps on A12 are all associated directly with the regulators, which I've taken as good so far. All the caps on the board are Tants. So far, they haven't measured well in circuit. The immediate task at hand here is clear for me though. I've got to modestly restore this area before moving on. No sense in breaking into this thing just to leave it worse than I found it. I'll secure things a little better, clean the area as much as I can with Alcohol, and clean all the connectors. More study is needed in here. This stuff does take time, but it's very peaceful for this old Bodger. Bear with me as I stabilize things. I've attached a photo of the seldom seen A12 board. JRH |
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