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Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders.

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Old 13th Jan 2021, 9:44 am   #1
MikeCross
Tetrode
 
Join Date: Sep 2016
Location: Tring, Hertfordshire, UK.
Posts: 57
Default Telequipment D67 Fault

My D67 no longer provides any traces despite all attempts to trigger one.
A green spot briefly appears in the center of the screen when switched off.
Are there any known issues with this scope?

I do have it's circuit diagrams and access to other test equipment.
Could anyone guide me in the right direction to finding this fault.

Mike
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Old 13th Jan 2021, 5:15 pm   #2
MotorBikeLes
Octode
 
Join Date: Dec 2012
Location: Kirk Michael, Isle of Man
Posts: 1,656
Default Re: Telequipment D67 Fault

OK, you have a spot at switch off, which says the HV side is OK. Probably an unblanking circuit problem, but check deflection first. I assume you have set ALL the controls as per the info in the instructions. Connect a test meter (250v range) from ground to one of the Y-plates and operate the vertical shift, you should see the voltage increase or decrease as the invisible beam goes up and down. The other plate should do the same (but in opposite directions) to the first.
Centralise the shift, and now check for horizontal deflection. Set the speed very low (say 1 sec per division) and with test meter connected to each X plate in turn (wrt chassis), you should see the voltage rise slowly then shoot down again. If OK, time to investigate the unblanking.
CAUTION. That part of the circuit is at HIGH VOLTAGE.
If you look at the PSU circuit, the bottom section shows the two voltages used in the unblank circuit, 13v and 45v windings, with the centre tap linked to the CRT heaters. I forget off hand, but expect well in excess of 1KV there.
It might pay to check TR261/261, but do this WITH POWER OFF.
If you remove the link to the HV part (670v winding), you can do some testing with a scope, but at this stage, try simple tests on parts with no power.
One other very common problem with the D67 series. The PCB is double side print, and the thro links (rivets in TQ speak) are regular dry joint sites. Carefully reflowing the thro links solves VERY MANY D67 faults.
Les.

Last edited by MotorBikeLes; 13th Jan 2021 at 5:17 pm. Reason: sp. winds to windings
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Old Yesterday, 7:26 pm   #3
MikeCross
Tetrode
 
Join Date: Sep 2016
Location: Tring, Hertfordshire, UK.
Posts: 57
Default Re: Telequipment D67 Fault

I can confirm that the 12 volt supplies are correct and the other tests you suggested seem ok. I get the correct time base driven signal from the output socket( front panel bottom right) I also see a small sine wave type signal at the GATE OUT socket but not sure if this is correct.
Is it safe to scope TR251 and TR252 (Unblanking amplifier)
It does look as if we are heading towards TR261 AND TR262
What should I see on CRT G1 and is this a safe signal to meter or scope
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Old Today, 6:26 pm   #4
MotorBikeLes
Octode
 
Join Date: Dec 2012
Location: Kirk Michael, Isle of Man
Posts: 1,656
Default Re: Telequipment D67 Fault

OK, you can check grid cathode voltage relationships, but you must realise these are at high voltage. You could measure from G1 to chassis, and similarly between cathode and chassis, turning brilliance up and down to see the brightness action. (Look at circuit and read manual). Do not do it unless you have a SAFE test meter. If you put meter between grid and cathode, the range is probably 30v to 90v negative grid wrt cathode, 30v being bright, 90v being very dark.
Regarding the TR261/2, switch off scope, unplug each transistor and check out of circuit. - I am pretty certain these are all in sockets.
Les.
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