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Old 24th Jul 2018, 10:33 pm   #1
ChosenPheonix
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Location: Aberdeen, Scotland, UK.
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Default Telequipment D67A restoration

Hi Folks,

I have recently come into possession of a Telequipment D67A oscilloscope and decided to make it my next project. Power light turns on however I am getting no trace on the screen on both channels. This is my first attempt at restoring an oscilloscope so trying to figure out what my options are.

I managed to find a copy of the manual and decided to follow one of the tests and noticed that the resistance on test point 149 (+115V line) is sitting around 7k ohms while the suggested value should be 1.5-3K. All other test points are fine.

Inspecting the components I can't find anything that sticks out, no burnt or loose parts.

Any advice would be greatly appreciated since I would love to get this scope up and running
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Old 25th Jul 2018, 1:29 pm   #2
orbanp1
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Default Re: Telequipment D67A restoration

Welcome to the forum!

I would start by checking all the supply voltages before I would do any other tests.
(that resistance test you mention looks kind of meaningless without the context)

Good luck, Peter
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Old 25th Jul 2018, 9:40 pm   #3
MotorBikeLes
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Default Re: Telequipment D67A restoration

I don't agree that the supply line resistance is pointless, though I would suggest you check all supply voltages. The point of the resistance checks is tp point to shorted components. A higher resistance than listed eliminates that however. I have checked these a few times before, but often found them a bit higher than shown.
The start point for checking any TQ scope is to set all the controls to "Initial operation" conditions always given in the manual.
Then start looking for faults if you don't get the expected display.
This could be as simple as having the main timebase set to "triggered" operation rather than "Normal"
25MHz bandwidth scopes, with main and delaying timebase and differential input front end (Y-Amp).
Les.
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Old 26th Jul 2018, 6:43 am   #4
Diabolical Artificer
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Default Re: Telequipment D67A restoration

Having just gone though a Telequipment scope fixing bonanza here's a few tips. Apart from checking rails -

1)Check cathode to grid voltage (brightness), grid should be about 10v ish below , IE negative of the cathode. So black lead of DMM on the cathode pin of the CRT, red lead on the grid pin. You should get - 10/20v ish and does the brightness adjust knob alter voltage?

2) Check both X and Y plates to see if they are the same, you could have a trace, but it could be off screen. So, leads of DMM on the X plate pins of CRT, it should read 0v or thereabouts. do the same for the Y plates. X and Y adjust should alter voltage like a seesaw. It's possible to short the X & Y plates to see if that gets your trace.

For both 1) & 2) you will need a pinout of your CRT or the pin #'s might be on the schematic.

3) If those are all ok you need to check the EHT which usually requires a HV probe, but you can check a +350v to ground rail say, then check from +350v to +700v *, this should read 350v, you can then "jump" from rail to rail as long as the difference is within your V max rating of your DMM. * These figures are just by way of example. The only tricky ones to measure without a HV probe will be the cathode and final anode (-1100v ish and up to +3500v ish)

4) Lastly put your DMM on AC volts and check the rails for ripple, anything over 2v ish will be suspect.

Andy.
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Old 26th Jul 2018, 3:14 pm   #5
MrBungle
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Default Re: Telequipment D67A restoration

I’m working through a pile of D83’s at the moment.

Good tips above. Almost certainly the capacitors in the power supply will be shot. Mine had Plessey electrolytics in it that had leaked. Had to do an extensive refurb on the supply that took hours!
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