General > General Technical Chat

HP 33120A waveform is distorted. Video inside. What is going on?

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fran:
Even though I pulled them and they showed "ok" in a tester?

Although I don't have the metal can transistors, I'm sure I'd have something I can substitute in to test at least.... I'll have a go and report back.

fran:
For info - the two output transistors are 2n5109 (npn) and 2n5583 (pnp)

Long obsolete now in both cases - what would be recommended as a replacement - the signal generator goes to 15MHz.

fran:
OK, scrap that last post.

I put in a pair of B139/BD140 that I had in the stash - the clipping is still there..... so I think its not the output transistors.

nctnico:
Get an oscilloscope and trace the signal path. That will be more fruitful than randomly replacing parts. Before anything else: check the power supply rail voltages. I assume there is a service manual available for this unit; start by going through the fault finding flowchart.

fran:
Good advice.

The signal is OK all the way to the output amplifier - so this is where the fault lies but it is complicated, hence me scratching around looking for info and help.

Voltages are all OK.

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