Component Tester Fault

[Noidzoid]

Where did you get the new caps from so quick, and how is it on other wave forms.

RS Components. Ordered  before 20.30, free P&P, received next afternoon.  I am very impressed. Seemed good value too. (Although they couldn't send me the 60/40 solder I ordered. Restricted under some regulation I believe)

Other waveforms seem to display fine on channel 1 but appear unstable on channel 2.  If I'm right it looks like a triggering problem on that channel only, is that possible?

[StillTrying]

"If I'm right it looks like a triggering problem on that channel only, is that possible?"

Often a dirty switch.
There's 2 "Trig Drivers", one from each channel, and the CH1/2 selection in the middle of the block diagram, but I can't find them on the schems.

[Noidzoid]

"If I'm right it looks like a triggering problem on that channel only, is that possible?"

Often a dirty switch.
There's 2 "Trig Drivers", one from each channel, and the CH1/2 selection in the middle of the block diagram, but I can't find them on the schems.

The actual selection button/switch for CH1/2 on the front panel does seem a little stiff/slow. I shall investigate.

[Noidzoid]

Is there a universally accepted product/substance/method for cleaning switches etc.
Servisol Super 10?
Isopropyl/Isopropanol?
WD40  Contact Cleaner?
Halfords Electrical Contact Cleaner?
Any or none of the above?

[Noidzoid]

Reason channel switch was slow/stiff was the pushrod was 90° out and was fouling on the casework (button end where there is a bend in the rod not actual switch on the board end)......easy fix!

Now though CH2 isn't picking up any signal at all. Just a flat line.........?

I thought maybe the misaligned rod may have upset the switch internals but jiggling it about didn't even cause the displayed line to flicker with a signal being fed in.

[AVGresponding]

I like plain WD40, from a 5 litre can, not the spray stuff, then a high melting point grease like white grease to lube afterwards.

The bent pushrod might have put undue strain on the switch, which might now not be contacting properly, I reckon you'll have to jiggle it until you get a result.
It seems a standard type if you have to replace it, just the stupid plastic adapter is a Hameg special   

[Noidzoid]

I thought maybe the misaligned rod may have upset the switch internals but jiggling it about didn't even cause the displayed line to flicker with a signal being fed in.

I like plain WD40, from a 5 litre can, not the spray stuff, then a high melting point grease like white grease to lube afterwards.

The bent pushrod might have put undue strain on the switch, which might now not be contacting properly, I reckon you'll have to jiggle it until you get a result.
It seems a standard type if you have to replace it, just the stupid plastic adapter is a Hameg special   

That's good. I have both of those on the shelf. (WD & whitegrease). Thanks.

Already done the "jiggling" with a slight bias in all directions to hopefully make even the slightest contact and change in trace. Short of replacing the switch (which may not even be the problem of course), I wonder if there is a way to bypass the switch to make the connections necessary for CH2 to opperate. I will have a look to see if it is that simple.

[Noidzoid]

I think the CH1/2 switch is working. Using the common pins on the switch and testing for continuity to others, the changes between pins are quick and consistent.

Following tracks, the signal is arriving at these sockets in the same fashion.

Ch1 selected


Ch2 selected

[Noidzoid]

There's 2 "Trig Drivers", one from each channel, and the CH1/2 selection in the middle of the block diagram, but I can't find them on the schems.

Will these drivers be actual physical components?

[StillTrying]

There's 2 "Trig Drivers", one from each channel, and the CH1/2 selection in the middle of the block diagram, but I can't find them on the schems.

Will these drivers be actual physical components?

I would think they're active buffers, but I still can't find that diode switching on the schem. (too busy to study it ATM).
If CH2 is still flat lined I think you must have disturbed something.

[AVGresponding]

I suppose a place to start is looking for any measurable differences in the trigger stages, also I suppose it's possible IC270 or IC271 have been damaged by static discharge..?

[Noidzoid]

Will these drivers be actual physical components?

I would think they're active buffers, but I still can't find that diode switching on the schem. (too busy to study it ATM).
If CH2 is still flat lined I think you must have disturbed something.
[/quote]

I have very similar showing the same trigger drivers in my book.

I think it makes perfect sense that I disturbed something, so I will be going over all the things I moved that I can remember.  I thought/hoped I had found the problem, one of the long plastic ribbon plugs/sockets wasn't pushed fully home but it made no difference so I think it was probably pushed far enough to make good contact in the first place.

Thank you for your help so far, and I appreciate your time has been given while you could have been busy doing other things.

[Noidzoid]

I suppose a place to start is looking for any measurable differences in the trigger stages, also I suppose it's possible IC270 or IC271 have been damaged by static discharge..?

Very possible. I must confess to not being very careful about static, only going as far as to not touch the pins on the IC I removed.

[StillTrying]

"Will these drivers be actual physical components?"

There's the 2 Trig Drivers, the 2 TRs each, how they work with differential inputs I don't know.

Nothing around the Trig CH1/CH2 SW or those Trig Drivers could explain the now flat lined CH2.

[Noidzoid]

There's the 2 Trig Drivers, the 2 TRs each, how they work with differential inputs I don't know.

Nothing around the Trig CH1/CH2 SW or those Trig Drivers could explain the now flat lined CH2.

I am trying to keep up but this learning curve I'm on is very steep. I will revisit this and try to catch up.......

While poking around I did notice a three leg component (I think it was a transistor) that was rubbing on the shaft of the X-Mag/X-Pos switch.  One of the legs looked weak so I soldered the weak looking bit (just in case).

Whether what I did next makes sense to more experienced fellows on here or not.  It did to me..........sort of.......

As I have a problem on CH2 and not on CH1 I thought what obvious physical parts could be swapped around?  If the problem stays on CH2 or moves with the component/s it would give a clue.  With this in mind I swapped the following....

I did intend to swap the smaller plates on which are mounted the BNC sockets also but they, unlike the larger metal boxes, are handed.
Everything soldered/fitted/screwed back in and fired up......... everything is the same, so at least that is a large number of the internals out no longer under suspicion.

[Noidzoid]

Also took the opportunity to replace another cap as I had easy access and surplus 1000μF 25v ones from earlier. It looked the same as the others I replaced so I thought it made sense.

[StillTrying]

It's always worth having a look for dry joints while your there, sometimes they're almost impossible to see, but the component leg moves a bit.
If those boxes are identical, after some checking you might be able to swap them to give some idea where the problem with CH2 is.

[Noidzoid]

It's always worth having a look for dry joints while your there, sometimes they're almost impossible to see, but the component leg moves a bit.

OK. Will do. Thanks

If those boxes are identical, after some checking you might be able to swap them to give some idea where the problem with CH2 is.

Sorry, I didn't make myself clear :-(
The two largest metal boxes in the above picture (each one of which are soldered together) with the amplitude knobs attached are what I did swap around.  Before which I unsoldered these boxes and had a look inside for anything obvious, soldered the boards back in and the boxes back together (my inexperienced eye saw nothing).
After putting/soldering everything back together I fired it up again and although the amplitude boxes had swapped places, there was no change in behaviour.  My conclusion is that the problem is beyond these boxes.

[StillTrying]

"Sorry, I didn't make myself clear :-("

You probably did, but it's hard for me to follow because I don't know the overall physical layout of the scope, and the pdf is low quality.

If you're powering some parts up while disconnected, check they have a ground connection, it looks to me in some places there's no 0V on the connectors, and they're just relying on the metalwork for the 0V.

"everything is the same, so at least that is a large number of the internals out no longer under suspicion."

Yep, I think the CH2 problem must be around the "Intermediate Amplifier" then, somewhere , maybe not the intermediate amplifier itself, maybe the 'Chopper Generator' and 'Ch. select' is preventing CH2's signal appearing at the input to the delay line. Good luck.