I too have spools of resistor in the garage.. And tubes of chips, big boxes of caps, etc.

Far as that probe I would take care.. I had a HV probe way back and was still nervous about using it.

 

It's all transistors, no valves or ICs.

I haven't used it for a couple of days, I'll check the low voltage side before I even think about the high voltage side.

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I've got a better 'scope so the old one got shut away in the cupboard for a couple of years.

Recently I've been thinking about getting rid of the 'scope. I didn't have the heart to throw it out so I was going to give it away.

I switched it on to see if it still worked, the intensity oscillated as it had done before. I took the cover off and took a photograph of the circuit board. I replaced the cover, turned on the power and to my astonishment it had made a full recovery!

It works perfectly now, no oscillation, no buzzing, all is well!

Why has it suddenly started working perfectly?

Could it be a loose connection or a pot setting?

I put it away on top of the cupboard (a producure that involed subjected it to some minor banging around) and got it out again, put it on my bench and turned the power on and it still works fine?

I'm at a total loss as to why it's made such a good recovery.

It turns out that I was wrong about the bandwidth specification, it goes up to 15MHz. I assumed 1MHz because I was using it with an uncompensated probe before which limited the bandwidth.

I don't know what to do with it now, it makse sense to get rid of it but I feel some stange attachment to it. I don't feel comfortable selling it because I wouldn't trust it not to fail pretty quickly.

Here are some pictures, it's a great newb 'scope as it's simple and very easy to use, with not complicated features.

Attached Thumbnails

   

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It's funny, 2 plus years later and it works after removing the cover.

I've seen that with other electronic items. Pot/something was corroded and cleared, cracked solder joint mated up when you locked down the lid, etc. I've picked up a dead computer, got it to the office and it worked fine, returned it and never heard back about it.

If you have a new one, I would sell that one. Sell it cheap and the new person might get a first real project tacking all the solder joints.

 

I spoke too soon, the oscillation problem has returned.

It must be a loose connection, it's the only thing that would expain it.

I'll have another look at it, if there's nothing obvious then I'll give it away.

On second thoughts, even if I fix it I think I'll give it away. I don't trust it and there's no point in having a piece of test equipment I don't trust.

Don't get me wrong, it's still functional as it is and would be fine for a first 'scope.

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If you tap on it (good tap) does it clear up for a second or two?

If not I would think a bad cap somewhere.

Too bad you're in England, I would give you a few US bucks for it, but the shipping would outweigh that probably. If you are going to give it away, let me know the shipping and handling cost .

I used the same Gould scopes years ago. We never really had a problem with them. You got the machine that was made on a Friday I think.

 

Not quite: I've tried tapping it and I can't get it to stop oscillating.

Possible but that wouldn't explain why it works for awhile after the case being remove then replaced, then suddenly stops oscillating.

I can't see myself dragging it all the way down to the post office to get it weighed.

It is very old so what do you expect?

It's still very usable, the oscillation is only a real problem at low intensities and it caused the waveform to jitter very slightly. I imagine that someone reading my posts here might think that it's worse than it really is. Unfortunately I don't have a video camera to record it or I'd post a video.

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It's an old scope, but a scope is a scope outside of the CRT being burned or it being really out of calibration.

The problem with yours sounds like it just bugs you, but it works. I would give it to a local for cheap and tell them keep the brightness up

Someone new in electronics would not have a problem with that. Like I said I would take it if shipping was not a pain just to have one in a place I do not have one.

Sounds like a CRT drive/circuit issue. Something breaking down with the pot on intensity. But the fact it sat then worked for a bit, probably not the pot.

 

Well it started working perfectly again so I decided to have another look at it.

I took the bottom cover off; something I haven't done before. I noticed that a 350V 100µF capacitor had gone (the big blue one pictured in the attachment), the safety valve had blown and there was a small spot of gunge on it.

I replaced it with a Rubycon 400V 100µF 105°C capacitor from an old SMPs. The replacement capacitor is much smaller and the safety is on the other end so I left a small space between the capacitor and the case in case it blows.

I powered it up and the 'scope still works perfectly. I suspect the big red capacitors may have gone bad too so I'll replace them when I put my next Farnell/RS order in.

Attached Thumbnails

   

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I've had another problem with it oscillating then cleared up again.

I've had a go at calibrating it but it's not possible without the manual. I'm loathed to replace all the electrolytics only for it to still keep doing this.

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Here's a picture of the HV board.

The channel A gain selector control has no gone very stiff.

I've decided that I'm going to get rid of the 'scope.

If you want it, send me a PM, I won't charge anything apart from shipping.

Attached Thumbnails

 

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