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Electronics => Repair => Topic started by: gkmaia on August 02, 2019, 02:46:19 am

Title: Agilent 54621D turns on but no CRT
Post by: gkmaia on August 02, 2019, 02:46:19 am
I am interested to buy an Agilent 54621D that power on and highlight some buttons, but has no display.

I did read some posts here about this scope and seems there are quite a few people who did some work on those.

Is it an issue anyone here has come across already?

Most likely an issue related to the CRT control board? CRT coil?

Or could it be something more complex like CPU not being able to boot up therefor not initialising the display?

If CPU fails to boot would it likely highlight some buttons or not any?
Title: Re: Agilent 54621D turns on but no CRT
Post by: Original on August 02, 2019, 05:28:14 pm
Assuming that you have checked all voltages especially crt grid voltage (does the crt it light up?).
After that check the electrolytic capacitors on the video board. They are notorious for failing (like mine). check the brightness pot for discontinuities.

After that you could try to probe horizontal / vertical sync pulses and then for the video signal. Check out page 13 here: http://bee.mif.pg.gda.pl/ciasteczkowypotwor/HP/54601A_Schematics.pdf (http://bee.mif.pg.gda.pl/ciasteczkowypotwor/HP/54601A_Schematics.pdf)
Schematic is for model 54601, but should be the same as yours.
Title: Re: Agilent 54621D turns on but no CRT
Post by: gkmaia on August 02, 2019, 10:34:56 pm
Quote from: Original on August 02, 2019, 05:28:14 pm
Assuming that you have checked all voltages especially crt grid voltage (does the crt it light up?).
After that check the electrolytic capacitors on the video board. They are notorious for failing (like mine). check the brightness pot for discontinuities.

After that you could try to probe horizontal / vertical sync pulses and then for the video signal. Check out page 13 here: http://bee.mif.pg.gda.pl/ciasteczkowypotwor/HP/54601A_Schematics.pdf (http://bee.mif.pg.gda.pl/ciasteczkowypotwor/HP/54601A_Schematics.pdf)
Schematic is for model 54601, but should be the same as yours.


I have no access to the scope prior purchase. But from what the seller told me it turns on but CRT do not light up.

Really hard to do this troubleshooting based on guesswork.

I imagine this is a digital scope so all probing signals go to a ADC then to the processor, then DAC to the CRT. Also the buttons in the front panel would only light up if the processor send the instructions to do so.

"By turns on" I can start to believe the main board and power board maybe fine.



Title: Re: Agilent 54621D turns on but no CRT
Post by: SilverSolder on August 03, 2019, 12:14:27 am

Just don't pay too much for it...   at worst, it can become a parts unit.