"new" scope screen all blurry - help

[chancecasey]

Just got my tek 2232 - I was so excited - my first scope - then, crap.

It powers up, and proceeds to show a bunch of blurry rectangles. Pushing the functions moves them around a little but that's it.

When I push the beam locator, I get a very bright, solid, vertical, rectangle. Everything is a rectangle, and turning the focus knob has absolutely zero effect.

I am so pissed at the ebay seller. The scope is not the one pictured in the ad, and they said "passed basic operation test". Hmm what operation is that? "yep, it weighs 10 pounds, just like the manual says. pass!"

Any idea what is wrong?

 

[ericgibbs]

hi chance,

Some ideas, if you havn't already tried them.

Check the astigmatism control setting.

Check the mains voltage selector is set for your local voltage.

Low EHT is quite often a cause of focussing problems, if the CRO has been stored in a damp environment, the EHT could be leaking away.

Turn down the brightness/intensity until you can just see the trace.
Leave the CRO running for a few hours, to see if its a dampness problem.
[until you have confidence in the CRO, don't leave it unattended during this test].

If this dosn't work, turn OFF the CRO and disconnect from the mains.

Leave the CRO off, for an hour or so, remove the covers and using a 100K
resistor in series with a grounding wire connected to the CRO chassis, discharge any point you want to touch/measure, BEFORE you measure.

Do a visual check, of the CRO, a wire/connector may have come off in transit.

Take CARE the voltages can be lethal, dont work alone when doing the following checks.

If you have the manual, get a EHT test meter and check the EHT, and at the
tube base check the Cathode and Focussing potentials.[ and heater voltage]

If these all check out, measure the tubes 'beam current' , refer to the manual
for the value [ in the order of 100 to 200 microamps]

If this is low then I suspect you have been sold a 'turkey'

Regards
EricG

Let is know how it goes.

 

[picasm]

I don't know what could be the fault but you can download a service manual from:
**broken link removed**

 

[chancecasey]

Found the astig adj, right next to the CRT. So let me get this straight, I turn it on, stick a metal screwdriver down in there where 5KV is nearby, and don't do it alone? Ummm, Yeah. Not feeling too good about this.

 

[ericgibbs]

hi chance,
If the 'astig' pot is internal there is a good chance to consider its not been disturbed, leave it alone at this time.

Many CRO's have a external user operated control, this is the type
to which I was referring.

Did you download the manual, I did for reference.

Regards
Eric

 

[chancecasey]

ok - not the astig - i powered up, grounded anything i was going to touch with amp meter in series just to know those things are safe to touch, adjusted astig, no effect.

have not tried leaving it on for a few hours but nothing looks damp, guess i should try this next.

what is an EHT meter?

 

[chancecasey]

oops - too late. how sensitive are those pots? i'm pretty sure i got it close to where it was.

 

[ericgibbs]

hi chance,

Basically an EHT meter is 'extra high tension' meter, designed for measuring kilovolts and it uses special probes to protect the user from electrical shock.

If you don't have access to the proper equipment/technical assistance and the damp 'soak' test dosn't cure the problem then you will have to contact your local repair shop.

Contact the seller and tell him of the problem and get his written agreement
that he is prepared to pay for the repair or get your money back or a replacement CRO that works.

Eric
Sorry to sound downbeat, but I don't want you to get injured trying to fix it, if
you dont have the experience.

BST: 19:20
EDIT: thanks for the response, good luck Eric

 

[chancecasey]

no, I appreciate it very much. i know my limits. I already sent the seller an email - we'll see what they have to say. my crappy little multimeter is limited to 500V. guess i'll start looking for a shop - shouldn't be too hard around here in silicon valley.

 

[chancecasey]

I assume it's ok to run the soak test with the cover off - as long as i give it plenty of room and don't touch anything?

i'm running the probe test/adjust square wave thing. If I crank down the seconds/div, I can kind of make it out, but, like I said, what should be a "line" is a solid rectangle.

 

[picasm]

If you think it may be something wrong with the focusing section, then have a read of the newsgroup post below, it seems that they can suffer from burnt-out resistors in the focus circuit?

https://groups.google.co.uk/group/s...=tek+2232+focus&rnum=1&hl=en#5ce5f3fc610ff476

 

[chancecasey]

Well, the focus does absolutely nothing so it's worth a shot. Unfortunately my multimeter does not measure 500Kohm. The resistors do not look burned or brown, but a reading on the meter would be the only way to know for sure.
Of course, the thing may have been dropped and has a bad tube now for all I know.

 

[audioguru]

Does any used test equipment sold on Ebay work properly??

"If it breaks, sell it on Ebay"

 

[Andy1845c]

Does any used test equipment sold on Ebay work properly??

"If it breaks, sell it on Ebay"

I hope some of its good. I've been trying to get a scope on there. This topic isn't real comforting.

 

[chancecasey]

OK so I have some somewhat-good news. I went out and frapped down $50 to get a "decent" multimeter, and one of the 510KOhm resistors in series for the focus circuit is completely open - 20MOhm setting, still has infinity. I also picked up a selection of carbon comp resistors while I was there. I have to take the kids to Chuck E Cheese now (yeehah), but I'll post up the results of my repair work later tonight.

 

[RadioRon]

Does any used test equipment sold on Ebay work properly??

"If it breaks, sell it on Ebay"

Yes some of it does. But as I'm sure you know, one has to have one's "bs detector" and "rip-off radar" and "honest dealer scanner" and "paranoia analyzer" and "suspicious seller sensor" all running at full throttle for any Ebay deal. Even the slightest odor is reason to abandon a deal. I've only been ripped once and in retrospect the signs of illigitimacy were so obvious that I could kick myself. Ebay is a lesson in what all marketplaces would be like if there were no law and order.

 

[chancecasey]

FIXED!!!

Thanks for the link, Picasm. It was all just a focus issue. Ran all the diagnostics and a couple of them failed, including one of the trigger tests

Hopefully this piece of junk will do what I need. $130 and a $0.15 resistor - guess I can't be too picky. Debating whether to leave a neutral or negative rating for these clowns on eBay. "AS-IS. Passed basic operation test" does not describe the condition this unit was in in my opinion. I'm pretty sure that resistor didn't pop while the thing was in transit. If they saw what I saw on the screen (which was a bunch of garbage) then they clearly were being misleading. Maybe they just never fired it up. I'll sit back and see what they offer to do in response to my email. I guess if they try to make it right somehow that's all I can ask for.

 

[Nigel Goodwin]

I would suggest a highly negative rating, they obviously sold it knowing full well it was faulty!.

 

[mvs sarma]

OK so I have some somewhat-good news. I went out and frapped down $50 to get a "decent" multimeter, and one of the 510KOhm resistors in series for the focus circuit is completely open - 20MOhm setting, still has infinity. I also picked up a selection of carbon comp resistors while I was there. I have to take the kids to Chuck E Cheese now (yeehah), but I'll post up the results of my repair work later tonight.

Hi

perhaps you are on the right track-- but-- why not wait for ebay to give you a replacement - instead ??
I f you want to go ahead try to follow the precautions below.
dont apply DMM near to ETH sections or near EHT transformer -- i fear you will loose it. take care of SHOCKS-- and be cautious dear

 

[picasm]

Great to hear you fixed it.

I think the ebay seller mislead you a bit - he really should have just said it was faulty rather than saying it had passed some "basic test".

I am wary of buying as-is stuff from people who specialize in it, they know exactly what they are selling an should not try to mislead buyers into thinking it may be ok or only have a slight fault.

There is a useful ebay guide for buying scopes -
**broken link removed**