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Old 20th Sep 2017, 8:21 pm   #1
qsilver
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Default Telequipment D43 Timebase

Someone kindly gifted me one of these today complete with the full manual - both look to be in great condition. It has the TD42 Timebase and two Type A amplifiers.

I took off the covers and used compressed air to clean off a lot of dust from the valves and circuitry, checked the Type A amplifier modules and all looks to be ok, no bulging capactitors.

I powered it on with a DBT and it started to come on so no shorts.

I then powered it up on mains and tried putting a sinewave through the amp channels. After some tweaking on the front controls, I could see two verticle lines on the screen, quite bright, but no waveform just a verticle line. The line gets larger and smaller when the input varies.

From this behaviour, I thought it's most likely a problem with the timebase as it isn't running left to right?

I wanted to know if there are any things to check first that can commonly happen on these. One thing I have noticed is that the Timebase module does seem to rattle a little in the case.

Has anyone worked on one of these before?

Thanks!
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Old 20th Sep 2017, 8:24 pm   #2
TonyDuell
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Default Re: Telequipment D43 Timebase

I think I worked on one many years ago... With a similar fault

From what I remember there are some germanium diodes in the timebase unit, and they had all gone leaky. Replacing them got it working.
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Old 20th Sep 2017, 8:30 pm   #3
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Default Re: Telequipment D43 Timebase

Hi.
The timebase is notoriously troublesome on these scopes. Mine was forever playing up.
The above advice regarding diodes is good, and since you have the manual I would check the voltages around the time base circuit. I found those small carbon resistors tend to go high or open.
If you have another scope, have a look at the ramp waveform as well.
Lack of timebase could also be linked to the triggering, which was never brilliant either.
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Old 20th Sep 2017, 8:39 pm   #4
qsilver
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Default Re: Telequipment D43 Timebase

Thanks for the fast replies! I do have another scope - a Kenwood CS-1575A I've been using it for a number of years now - would that be okay? Just thinking about high voltages etc.

I'm in no rush to get this one going, would it be best to remove the timebase module and check all the carbon resistors and germanium diodes etc?

What could be the issue with triggering? Could I feed in an external trigger source like a sine/square wave to check?

I've noticed the switch for One-shot and normal doesn't "click" between positions...
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Old 20th Sep 2017, 8:59 pm   #5
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Default Re: Telequipment D43 Timebase

Is the red variable time/cm control turned clockwise towards the 'cal' position? The timebase is switched off if it is fully anti-clockwise. Likewise the trigger level should be set to 'auto' and the 'stability' control adjusted to see if the timebase will run continuously.

I have found that when calibrated correctly, the D43 timebase will trigger reliably. I think Motorbike Les prduced a sheet on the Forum defining things to check in the D43 timebase, including various carbon resistors and the aforementioned germanium diodes, if they have not already been replaced with 1N914s or 1N4148s.

https://www.vintage-radio.net/forum/...10&postcount=2

Ron

Last edited by ronbryan; 20th Sep 2017 at 9:04 pm. Reason: Added link to Mototbike Les D43 timebase check list
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Old 20th Sep 2017, 9:25 pm   #6
MotorBikeLes
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Default Re: Telequipment D43 Timebase

Ronbrian has just said most of what I was going to say. Stability must be set as he says, that will get a trace that will free run. However, the TD42 has a single shot position as I recall, so make certain it is not set for single shot.
The manual does tell you where to set all the controls for a first time operation. I may still have a few bits; for example if the "rattle" turned out to be the prongs fallen off the trigger connect board, I have them. (Not suggesting they will, I don't think I ever replaced any, but you never know.
Good luck, Les.
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Old 22nd Sep 2017, 1:57 am   #7
qsilver
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Default Re: Telequipment D43 Timebase

Quote:
Originally Posted by ronbryan View Post
Is the red variable time/cm control turned clockwise towards the 'cal' position? The timebase is switched off if it is fully anti-clockwise. Likewise the trigger level should be set to 'auto' and the 'stability' control adjusted to see if the timebase will run continuously.

I have found that when calibrated correctly, the D43 timebase will trigger reliably. I think Motorbike Les prduced a sheet on the Forum defining things to check in the D43 timebase, including various carbon resistors and the aforementioned germanium diodes, if they have not already been replaced with 1N914s or 1N4148s.
It seems it was an error on my part this time, I thought the calibration in the "Off" mode would just run it at the specific time on the second selector. I turned it from off to CAL and I have movement! So at the moment it looks like its working quite well.

I tried testing it and only noticed that I cant get the bottom line as clear and sharp as the top, but its quite negligible.

Again with the bottom line and so, the lower Type A amplifier, the amp seems a little unstable DC-wise and the line tends to gently rise and fall slightly compared to the top amplifier which is rock steady.

Would you still recommend I look into replacing a few parts on the amplifiers and timebase modules etc? Prevention is better than cure...?
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Old 22nd Sep 2017, 8:49 am   #8
ronbryan
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Default Re: Telequipment D43 Timebase

On the 'A' amp that drifts, you could feed in the calibrator signal to that channel, adjust the timebase and trigger controls to get a stable waveform and see if the square wave amplitude alters when the trace drifts up and down. If the trace remains substantially the same size, it could be 'Y shift' problem, if the trace amplitude changes, then the gain of the 'A' amp is changing.

You could try cleaning the x1/x10 switch contacts on the 'A' amp with a small amount of Servisol 10 and a cotton bud or operating the switch several times to remove oxidation.

Ron
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Old 22nd Sep 2017, 8:47 pm   #9
Tim
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Default Re: Telequipment D43 Timebase

As I recall focus voltage is derived from a potential divider including the focus pots. Check the resistors each side of the controls. I also STR they are located somewhere unexpected, on the main chassis by the focus pots I think.
Real dual trace here, none of your "chopping" nonsense, two guns, two traces two focus pots etc. More expensive tube but a clearer trace.
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Old 24th Sep 2017, 9:17 pm   #10
qsilver
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Default Re: Telequipment D43 Timebase

Quote:
Originally Posted by ronbryan View Post
On the 'A' amp that drifts, you could feed in the calibrator signal to that channel, adjust the timebase and trigger controls to get a stable waveform and see if the square wave amplitude alters when the trace drifts up and down. If the trace remains substantially the same size, it could be 'Y shift' problem, if the trace amplitude changes, then the gain of the 'A' amp is changing.

You could try cleaning the x1/x10 switch contacts on the 'A' amp with a small amount of Servisol 10 and a cotton bud or operating the switch several times to remove oxidation.
Tried this, and the waveform doesn't get bigger or smaller, just the line wavers up and down. I tried checking the 10x/1x switch and something might be amiss here. I get almost no signal display on 1x and a decent amount on 10x. The calibration pots seem dirty as the traces move around a lot as you turn them but I don't get any signal on the 1x, just a slight waveform that looks like low level hiss or noise.

I wondered about it having two "guns" the traces are fantastic compared to my other more modern scope, incredibly clear. The extra function on the X such as being able to zoom in and move it around etc are very useful.

I did have a job getting it to trigger last night, At first it wouldn't run, so I put it into single shot mode and used reset to trigger it a few times then upped the X timebase and triggered again. After this it worked fine. Looks like it needed a sort of kick to get it going.

The other thing I wanted to mention is a strange smell it has. I have this and a Radford DMS 2 that both have this slightly plastic-y foul smell. I wondered if it might be the circuit boards or if there's a reason or explanation for it.
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Old 29th Sep 2017, 11:21 pm   #11
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Default Re: Telequipment D43 Timebase

I've been doing a little research on the web about the strange smell that comes off the scope. It's a little unpleasant after being on for a while. Could it be that the oscilloscope has PCB's made from Bakelite and it is the Bakelite getting hot that I can smell?
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Old 29th Sep 2017, 11:35 pm   #12
ronbryan
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Default Re: Telequipment D43 Timebase

The multi-tapped power resistor on the tube side of the cabinet runs pretty hot and may be a source of a dry dusty sort of smell. As it is close to the top of the chassis, it is easy enough to inspect.

Other culprits could be the long tubular STC K8/50 selenium high voltage rectifiers on the timebase side of the chassis.

Ron

Last edited by ronbryan; 29th Sep 2017 at 11:40 pm.
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Old 29th Sep 2017, 11:37 pm   #13
qsilver
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Default Re: Telequipment D43 Timebase

Maybe its the sleneium rectifiers.. its not a dry dusty smell, more an acrid melting plastic smell... it's there faintly even when its off but is much much worse when its switched on, it stinks the room out.
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