Telequipment D61 'scope

[dr pepper]

I have a relic D61 from the 70's, its mainly used for iffy jobs on high voltages so I dont blow up my newer philips I recently aquired.
The trigger circuit stopped working, and using my other 'scope and a sig gen I traced the problem to the trigger amp, one of the transistors wasnt making connection in its socket, so its now soldered direct.
The trigger still isnt good on certain ranges, it'll trigger ok for a second if I move the trigger switch from normal to tv and then back again for a second or so then fail, most of the ranges work ok, I think maybe a cap is leaking or breaking down or maybe the h timebase switch is bad, I've cleaned it a couple of times.

Another issue that concerns me more is if you turn up the brightness past a certain point the displayed image gets bigger as if you just increased the input signal, I'm thinking maybe power supply issue, the caps are original.

This thing probably should go in the skip however it has it uses and there is some sentimental value, my mrs bought it for me a while back

 

[Mr RB]

The brightness/size issue is called blooming and is a sure symptom of PSU not regulating very well. Most likely caps gone bad (as you said).

Bad caps will also give trigger issues, that's a common symptom too.

If you have an in-circuit ESR meter then go over all the caps, and replace as needed. I would also replace any smallish caps near hot spots like heatsinks or power resistors.

If you don't have an ESR meter then just do all the PSU caps and any small caps near hot spots.

Please don't junk it, someone would treasure that and fix it up even if you decide not to keep it.

 

[dr pepper]

Didnt know there was a name for it.

Yes I have a esr meter, and it does in circuit, and I have tested all the caps, 3 4u7 150v caps were slightly high and have been replaced, it didnt make much difference the scope still didnt trigger, only when I soldered the 2nd and 3rd stage trigger amp trannys in did the scope start to trigger properly (they were in sockets), theres still 2 or 3 ranges where the scope will trigger ok for a second then bomb out, making me think dodgy cap or range switch contacts, the trigger amp looks like it has variable bandwidth controlled by the range sw.

I've no intention of binning it, and it wouldnt be worth selling, its been usefull for odd jobs and is permanently connected up to my component tester gizmo. I have a biccy tin half full of salvaged high voltage psu caps so I'll replace the 3 main supply caps, didnt want to 'scope the ripple on them, messsing about with 200v signals isnt something I want to do with my good 'scope, thats what this one was for!

 

[Mr RB]

If you found corrosion issues int he transistor sockets it's worth going over all sockets etc, and things like the trigger pot and other pots and rotary switch contacts. If the pot is "crackly" you will get terrible trigger performance, likewise many of the rotary switch contacts are in series in the signal chain.

Spray with 100% evaporative contact cleaner or a pot cleaner, and work all the pots and switches. That might help a bit with the trigger. Good luck!

 

[dr pepper]

I squirted all the pots and switch contacts with switch cleaner, however I dont know if the trigger pot is crackly or not, that did concern me, looking at the output of the trigger amp on another scope there doesnt appear to be any crackles, if changing the psu caps doesnt sort it then I'll take out the trigger pot and check it off the scope, putting dc accross the track and connecting my tracer to the wiper I found to be an excellent way of finding noisy pots.

My switch cleaner isnt 100% evaporative, it leaves a lubricant, it is an insulative lubricant, we used it for repairing telly's for years, should I really use a 100% evaporative cleaner?, if so I'll get some.
You guys seem to mention deoxit a lot, we cant get that over here.

 

[Nigel Goodwin]

My switch cleaner isnt 100% evaporative, it leaves a lubricant, it is an insulative lubricant, we used it for repairing telly's for years, should I really use a 100% evaporative cleaner?, if so I'll get some.

No, it's mostly useless - WD40 type products (which leave a thin lubricant layer) are FAR, FAR better for cleaning contacts and pots etc.

 

[dr pepper]

And I used to shout at customers for squirting pots and boards with wd40.

The trig pot is an ohmeg which are easily available, but it has a pull switch which are made from unobtanium, if theres any doubt about the track I'll get a new ohmeg and take out the track and put in in the old pot.

 

[RichTheDude]

No, it's mostly useless - WD40 type products (which leave a thin lubricant layer) are FAR, FAR better for cleaning contacts and pots etc.

I would NEVER advise people to use WD40 as a contact cleaner. The thin lubricant layer slowly goes off and becomes sticky collecting dust, the lubricant layer increases the resistance of the contacts.

I tried WD40 when I was much younger, it led to a complete calamity. Contact cleaner exists for a reason, buy the proper stuff for the job!

 

[dr pepper]

I've only ever used contact cleaner, except for my bike exhausts where wd40 is great.