Electronics > Repair

HP54600B with spike problem with and without signal

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sacha:
Hi, I have a problem with my HP 54600B which at startup generates many spurious signals on the signal it displays. I couldn't find the manual with the diagrams. I wonder if any of you have the manual for this oscilloscope and if you have ever seen this defect. Thank you

I also ask if it is possible to reset the error you see. Thank you all

Runco990:
I'd check the power supply first.  They are known to leak capacitors quietly underneath where you don't see it.

Also once the scope warms up, run the self-calibration and see if it clears, as old capacitors get a little better as they heat up. 
Check visually for discolored tantalums on the main board.

I've been buying these scopes and fixing them for many years.  Not much goes wrong with them.  Usually a capacitor on the display, causing a compressed image, leaking capacitors in the power supply, sometimes a burnt tantalum, a dead NVRAM that holds the calibration settings.... aaand dirty controls.  Whew!

Measure for AC ripple and correct voltages on the power supply connector.

There are really no schematics for these as far as I know.  I think someone drew out the power supply and the display board, but not the main board.  Noise is likely power related anyway, as the main board is pretty bullet proof.

sacha:
Hi, thank you for the reply, in fact as soon as I turn it on the signal is very dirty and after about 15 minutes it disappears on its own. I tried to check the voltages coming out of the power supply but I didn't see any ripple and the voltage is around 5.10Volts. However, I noticed that if I cool the U33 the spikes return, perhaps it could be this integrated circuit or the timing of the signals is incorrect

iMo:
The U33 is a standard cmos sram (32kB). It could be a solder joint gets crappy. What will happen if you press a little bit on its package?

sacha:
Hi, thanks for your reply, actually the soldering all seems fine, I also tried using a pin to move the U33's feet but everything seems well soldered.

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