Products > Test Equipment
HP 8904A Options
TheDefpom:
I purchased one of these recently to fix it in a video for my channel.
It has a dead power supply, and whilst trying to trace the fault yesterday the filter blew up in front of me, I was actually recording a video for my channel at the time, so I caught it on camera !
I think I traced the dead power supply to Q4 being blown, an MJE18006, it is completely shorted out, so I am hoping that is all that is wrong with it (apart from the filter of course, I wonder if they were not really designed for 240V operation?), I wasn't able to find a proper circuit diagram for it either.
I will be posting a video to my youtube channel after I have finished piecing together the video sections, in case anyone wants to see the filter blowing out and the smoke.... it stank, my lab still smells badly from it today !
Video will be here (once it has finished uploading and processing... will be a multipart due to the need to get parts in):
SeanB:
Whatever drove that transistor is guaranteed fried, along with the emitter current sense resistor, the base resistor if there and of course the blown fuse. Bridge rectifier might also be blown. Replace them and the small electrolytic capacitors around the controller chip as well, and check the snubber resistor capacitor and diode is still intact.
Then run the PSU unloaded with a dim bulb tester, and see if it at least tries to start up and does not light the bulb to full brightness. May or may not run properly with no load, but should have some life on the secondary side.
douardda:
I did a blog post on my HP 8904A PSU problem and repair. It's most probably not very useful for you since the pb looks very different, but just in case. I did reverse eng. a part of the schematic.
https://whatever.sdfa3.org/tag/hp8904a.html
David
Envoyé de mon GT-N7105 en utilisant Tapatalk
TheDefpom:
I did find that blog when I was searching for info, a very interesting and helpful page, yours had a different fault to mine, but the power supply is the same one, I have saved the diagram to my records as I expect it will be needed, one thing I did notice is the ic numbers, mine are not lm393 but lm392.
TheDefpom:
I did some more investigation about the options once I repaired the unit I have here, I figured out the codes required for each option, and how to set it correctly, instead of using "FF" which results in trailing slashes due to invalid option selections (non existent options).
I did a video on my channel for this, showing what I found and demonstrating how to set the options.
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