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High voltage, big and the troubleshooting will need to be done live. You’ll probably want to 70004aa an isolation transformer and differential probes, and keep one hand on your pocket at all times.
Keysight Technologies (Agilent HP) A used or new for sale at used-line
The supply operates a high switching frequency and many parts of the circuit are shorted at DC, so I could not find this until I took both transformers out.
7004a confessed before that I killed a few components on the process, and I could not find replacements for some of them: Many suggested changing every capacitor in the board, something I was not going to do, I wanted to find what the fault really was 700004a capacitors turned to be ok:.
This paid for itself in just this repair.
And a final picture of the twin transformers in the working power supply. One day, it refused to turn on.
This last one required some improvisation because it is a quad-transistor instead of dual, and the DIP package is very different. I could see the power LED flash briefly upon turn-on and then Could this be fixed? Something was drawing more current than expected and the current-limit protection was tripping.
There is no way to check one of the blocks of the power supply alone, you have to give it power and hope for the best. After many hours of testing and probing, and and few components that exploded in the process most times my fault I found there was a transformer with a 14 ohm leak between primary and secondary.
I bought this cheap A color display as faulty. Do you see that suspicious potting that squeezed outside the can in one of them?:. You really need to know what you are doing before probing and testing a thing like this live.
This is the beast on the bench, that PCB looks very timidating to me. Home Projects Music Photo.
The block diagram was invaluable, this switching power supplies are complex. I built this “adapter” thing as a temporary solution, you too know what that means: Knowing I had nothing to loose, I went and opened the transformer can with a Dremel, and removed the resin with hot air and tweezers, carefully to not damage the windings. I was lucky to have bought a FLUKE D differential voltage probe this year at Friedrichshafen to the nice guy with grey hair and glasses that sells mostly Fluke stuff.
I was happy to find it actually worked This board is a latter revision than the ones that appear on the schematics but there are not many changes. Can you tell one from the other?
70004A Color System Display
I did not know where to start. I used a thin teflon tube and a copper wire to recreate the four turns 70004aa form the secondary and guess what, it worked!! You can see the power supply slowly increasing the current at turn on until it gets too high before it starts regulating the voltage, and quits.
There is a current sense resistor and this is what current looked at turn-on try:. No surpise, the secondary jacket was burned and touching the primary in one h.