HP 3314A Part 2 Troubleshooting (Power Supply and Voltage Safety Circuits)

This power on failure issue ended up being a minor repair but it forced me digging into the power supply & voltage safety circuits so I thought to include some of the info I learned while troubleshooting as part 2 and then I will soon make a part 3 about exploring the operations and unique features.
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TIMESTAMPS
1:30 -Power on issue and review of voltage protection circuits
8:35 -Supply voltages after the rectifier
10:00 -Short circuit detected while testing the power transistors
12:00 -Unplugged A2 ribbon cable removed short but power on failed with strange voltages
12:55 -Found tantalum capacitor shorting -15v on main board (cut one end)
13:50 -Found another tantalum capacitor also shorting -15v on Generator board
15:00 -Successful power on with only front panel display board
16:30 -How the voltage regulators track each other and 5v Buck Converter review
19:31 -Current Foldback safety feature in case of short circuit
22:30 -Successful power on with all boards connected (missing 2 filter caps)
23:56 -Compared minor ripples found on -15v to +15v and no real issues
26:20 -Output looks good

[@fabiom7104]

I really like the way you explain circuit diagram, well done! Thanks.

[@abdoolgafoor670]

Nice work, keep it, all the best for your channel. 👍

[@cs1chang360]

A very clever way, thanks

[@MrAppleimac01]

Hi could u help me pls I hv a display issue, however when I discount the same cable as u did. I get the screen and good voltages on the rails. When connecting the cable back I get on the rails +0.37 volts + 10.69 volts and 0.116 volts. Do u hv any idea where i should look?

[@Adam.Videos]

If voltages go back to normal when disconnecting the J1 ribbon connector, then I would suspect a shorted component on the front panel circuits. The display board itself is less likely to have short, but its smaller controller board right behind it (I think it's called A11 board though missing from my service manual) it does have some tantalum caps that could easily cause your issue. Check for a short with a multimeter on the supply lines on that board by itself and if appear shorted then you can try targeting the tantalum caps by cutting one end until you find the bad one. It's hard to help you much more than that here but I do wish you good luck!

[@MrAppleimac01]

Thanks Adam for the pointer appreciate it

[@Adam.Videos]

You're welcome and hope you can find the issue 👍

[@MrAppleimac01]

Thanks Adam for the pointer appreciate it, but its when i disconnect the J3 ribbon. I cant seem to see where this ribbon goes.

[@Adam.Videos]

J3 goes to the Generator board at the very bottom, the same board I had the second bad tantalum cap in my video. If you don't know how to get to that board you can watch Part 1 video