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Old 9th Aug 2017, 12:04 pm   #1
mindburner
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Default Telequipment D61A oscilliscope.

hi all

I have an old and quite battered D61a scope. I got it from ebay. Described as working, i.e. both traces appear, heart beat flatline style. The PCB covers were missing, not a good sign though.

Triggering initially seemed to be a problem at least on some of the ranges (1s etc)
However I have managed to get some of the faults ironed out

I used the service manual to adjust the triggering sufficiently by guesswork to enable a lock on most of the range.

I replaced most of the electrolytic capacitors and found that the trace quality an brightness are better.

I don't have a signal generator currently so can't do many of the calibrations in the manual but at least it seems to be fairly functional.

I have noticed a few strange things. One is a red wire sort of floating, not attached to anything. I see this has been mentioned before in posts and that a few D61 owners seem to have this so I assume this is an intentional choke or something or a bit of decoupling.

The inbuilt calibration signal square wave has wonky sides. Trapezoid. I must get a square wave from somewhere and check if this is the same.
Overall though a great scope for £20.

I made some new panels from plywood and cleaned the scope up. Should be handy for calibrating the analogue synths own.
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Old 9th Aug 2017, 9:53 pm   #2
MotorBikeLes
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Default Re: Telequipment D61A oscilliscope.

I think the cal waveform will always be "a bit wonky". The rise and top part are used to normalise your probe only. No big overshoot, not too much slope.
In DC coupled mode, the difference between the flat(tish) top and flat(tish) bottom represents the 1 volt (or whatever it says in the manual.
You can do a fair check on the calibration of the cal waveform but comparing with a 1.5v dry battery. Check that with your testmeter, ensure it agrees with the 'scope's display (use Y-cal adjuster), then apply the cal waveform. If that does not show correct reading, adjust the cal level as in book. Not sure if a twiddle pot, or "select on test" resistors.
Les
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Old 10th Aug 2017, 6:40 am   #3
Diabolical Artificer
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Default Re: Telequipment D61A oscilliscope.

The twisted wire you mention is supposed to be there as you have sumised.

You can get lot's of software online to generate sinewaves etc. Not least Audacity which can generate sine,square and sawtooth. It has a half decent spectrum analyser too, good for looking at your vintage synth's waveform's for fun if nothing else.

Andy.
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Old 10th Aug 2017, 1:59 pm   #4
mindburner
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Default Re: Telequipment D61A oscilliscope.

Thanks very much for the great replies. I have learned quite a lot from servicing this scope and it's nice to see an abandoned piece of vintage kit working for the want of a few capacitors. It's great the trace is no longer jumping around like a mad thing and hopefully will continue to work. Just need another bust synth now to fix

I have ordered one of those cheapo signal generators from ebay, so shall have a play with that.
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