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Instek GRS-6032A oscilloscope - display issues

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mdanh2002

Member
Hi,

I purchased a GW-INSTEK GRS-6032A oscilloscope from eBay a few weeks ago. What makes this scope interesting is that it's hybrid - supporting both analog and digital storage up to 30MHz bandwidth and 500MS/s sampling rate with just a press of a button. Anyway it was working well for around a week or two after the purchase when I suddenly noticed something interesting:

1. In analog mode, the display would be shifted down vertically, so the bottom status line showing voltage per division, timebase, trigger settings etc. is not visible. The top status line showing cursor readout remains visible, although it also moves down with the rest of the display.

Analog Mode Normal.jpg

By using the trace rotation I can see the the status line is still there, just not visible when the display is horizontal:

Analog Mode Rotated.jpg

2. The position of the traces for channel 1 and 2 can still be moved normally using the position buttons, but the readout and status lines cannot be moved. This is however by design.

3. The vertical display offset in analog mode is not constant, but appears to change randomly. When the problem first occurred, leaving the oscilloscope working for a few hours would result in the whole analog display moving up slowly, eventually reaching its intended position. However, currently this no longer happens. In fact - the analog display may sometimes bounce up and down repeatedly, and sometimes remain stable but only at the bottom quarter of the screen.

4. If the oscilloscope is switched from analog to digital mode by pressing the STORAGE button, then all traces and status lines will suddenly move up to their expected position. In fact there are no issues with digital mode, only analog mode:

Digital Mode.jpg

Suspecting some leaking capacitors whose capacitance will change as they get warmer after a period of usage, I opened up the oscilloscope for a visual inspection but found nothing interesting.

Any advice on what the problem might be? As the oscilloscope seems to have no other problem, my intention is to see if this can be a simple fix. If not, I will just live with the current issues until it gets more serious.

The photos of the analog and digital traces are attached to this thread. Other photos of the inside of this oscilloscope can be found at: https://www.dropbox.com/sh/dcuo1ceqjly32u0/AACrvv3hE1DQN_eyNf4kOMf9a

Thanks in advance for any suggestions.
 
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mdanh2002

Member
Thanks, let me study the Tek schematics. I have been trying hard to find the schematics for this oscilloscope but could only find the user manual. Any ideas where I should be looking for the dc restoration circuit on this oscilloscope? Was thinking I could unplug it for a while and test all capacitors for leakage using an ESR meter.
 
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mdanh2002

Member
I guess the service manual is available, just that not offerred to the public for download. Maybe their service centers or authorized repair centers have a copy of the document. If only every company is like Tek, providing detailed service manual for easy download from the website.
 

KeepItSimpleStupid

Well-Known Member
Most Helpful Member
I'm not sure they do it anymore. Some Agilent SM's are for sale at $400 USD or more. Keithley, which is now a Tek company, some of the online manuals are missing schematics, but paper ones have them.
 

mdanh2002

Member
I fixed the issue just by opening the oscilloscope and performing a simple cleaning up of the inside using a hair cleaner. Too much dust in there. As soon as I saw a few trim pots, marked for the status line, horizontal and vertical display and was trying to adjust them to see the effects, I noticed that the status line is displayed nicely and no longer hidden! I put the scope back again and it has been a month with the scope working perfectly! The status line issue seems to have vanished!

It's unfortunate that I never found out the real cause of the issue - perhaps some metal dust that intermittently short-circuited parts of the board responsible for the vertical display, which gets removed after my cleanup. The scope seems perfectly healthy now, still working fine after almost 20 years.
 
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