E-Bay purchased and listed as tested; Not true. Display partially failed all functions: boot forward. Bad area stationary on screen. About a 1.5 sq inch area flooded with active bright green/yellow pixels. Picture attached.

Opened case and everything visible without removing boards or accessing screen looks OK; caps etc. Connectors look OK.

Would appreciate any advise on how to proceed trouble shoot and repair OR recommend live with it.

 

That's a shame, looks like a decent scope too. Well that yellowing could be either physically damaged elements in the display or faulty memory (meaning some addresses are not working so what gets written isn't actually stored. Is that the only problem? the colored area? your post seems to be saying some tests failed too.

These things spring to mind:

1. Someone attempted to update firmware and messed that up, lost power partway through the update.
2. Physical damage to those pixel elements in the display.
3. Some region of memory misbehaving.

Can you get a trace? if you try to display signals does that work? does the scope have a self test? if you gently press the yellowed area, does it change color slightly?

Also look here - how to fix stuck pixels (yours look stuck as opposed to dead)

 

Thank you for the input. I really appreciate it. Sorry about lack of clarity in my message. The yellowing is the only problem I found at this time. I opened it up, and am confident it had not been opened previously and it was visibly pristine inside.

The yellowing is the only problem. I bought new probes and have calibrated using the scope generated sq wave and everything was OK. While doing that I tried most of the controls and settings and all seemed to work.

I will try a trace from on-line signal generator tomorrow. Please advise how to display signals? I will also try to connect external VGA monitor tomorrow.

No easy self-test that I can find. I have the maintenance manual and the my first reading implies all the referenced tests and calibrations are for technicians and seem quite involved. I will review all again and see if it addresses any memory tests.

Touching yellowed area does not change color or contrast.

I will now look at article on "how to fix stuck pixels"

Regards,

 

Its strange that you have nothing on the LCD screen at all besides the possible LCD yellowing fault, but that may be a setting you have it on. If as you say you have calibrated and it looks all goo, then I dont think its a firmware update issue, that generally seriously messes things up.

To me it looks like an LCD problem which changing the LCD, if you can find and acquire the part should fix? Your service manual should identify it or on the LCD panel itself.

 

Thank you for input.

I was incorrect due to looking at wrong owners manual; my 820C does not have VGA output.
Input signal from cell phone app today and have attached picture of display. All controls seem to function OK (based on my limited ability) except for the blob on the display.

I expect trying to find a replacement display would be next to impossible. Any suggestions for obtaining?

Regards and thanks

 

Thank you for input.

I was incorrect due to looking at wrong owners manual; my 820C does not have VGA output.
Input signal from cell phone app today and have attached picture of display. All controls seem to function OK (based on my limited ability) except for the blob on the display.

I expect trying to find a replacement display would be next to impossible. Any suggestions for obtaining?

Regards and thanks

The display might well be replaceable, see if there are any labels or brands etc on that display, it could be some mass produced unit used in a range of applications not just that scope.

It also wouldn't hurt to drop a line to: sales@instekamerica.com politely asking for any information they might be willing to share.