Telequipment D43 Help!

[notallbad]

Acquired the above in the hope it was in working order to learn how to use one, I already have a S51b needing attention - blew a fuse and not sure why and have not had the time to investigate - it honestly was not something I did.

Seems this one, D43 only half works.

I think I need to strip them both down and clean them out and service where necessary.

The problem is that the first trace appears on the tube but can not adjust via 'Y' shift, focus etc... Trace just appears as a thick band.

I shall have to get some photos up of the scope, body, internal components and trace signals to assist servicing.

Could we first start with how to open the case to expose the boards and also safety precautions, I had it on a few hours ago for under an hour, long enough for it to warm up and check if its in working order.

Any help would be greatly appreciated.

[notallbad]

Carry handle screws remove both side panels and 2 screws at the back remove the rear panel.

Found a red wire, either cut or disconnected from a component, on the 'main' vertical board that has the 'reset' button, time/cm etc...
Its between R173 and R159

[Duke_Nukem]

Hi and welcome to the forum.

If you undo the two screws used to attach the handle then the side panels can be removed. The plug-in Y amplifiers can be slid out by simply unscrewing the bolts on their left/right.

First port of call is a visual check, particularly are all the right valves in the right place and none missing. Some large resistors may look a bit burnt but they do run hot, so just check their resistance. Look at the bases of the electrolytic capacitors which may have leaked.

The second port of call is to check all the HT voltages are correct - there's about a dozen of them ! Also check the tube voltages - for example the focus should be around -500v.

This scope has two EHT's - +3.2KV and -1KV, the focus adjustments are derived from the -ve EHT so that'd be the first one to measure. Note that the EHT voltages are derived directly from the mains - a system referred to as "Widowmaker" and with good reason too!

The service manual is available here.

However - if you have not dealt with valve electronics before I would recommend you do not work on the scope. Sorry and all that, but they are complicated beasties with high voltages, not ideal for an initial introduction to valve electronics.

TTFN,
Jon

[notallbad]

Hi and Thanks Jon.

Afraid of that! Perhaps I shall just clean it up a little so I can see things more clearly, find what's missing, though all valves look like they have not budged in years and all appear to be there. There are a couple of discoloured resistors but caps 'look' good.

If possible I shall get pictures up. May need to do a few more posts before being allowed.

[ronbryan]

Don't move the 'cut' wires. They are a 'neutralising' adjustment for the X (horizontal) amplifier.

Are both traces de-focussed and not responding to the 'Y' shift controls, or just one of them?

Ron

[notallbad]

Thanks Bryan.

So looks like I need to check/test a few components to find any out of spec.

I do have the original user manual and probes that came with it, so at the very least I have some leads for future use but hoping to get this working still.

Originally Posted by ronbryan

Are both traces de-focussed and not responding to the 'Y' shift controls, or just one of them? Ron

Hi Ron.

Thanks, it's just the top one that does not adjust and de-focussed.

Rob.

[Fezziwig]

I have D83 I might want to get rid of.

[notallbad]

Flintshire, too far and expensive postage.

I'm sure I can get this one working with a little help, besides it does half work which is probably all I need for now.

[ronbryan]

What happens if you exchange the 'Y' amplifiers. Does the lack of 'Y' shift follow the amplifier or remain with the same de-focussed trace as before?

Ron

[notallbad]

Do you mean pull out both bottom trays and reverse them?

OK, reversed 'Y' amplifiers and waiting for warm up etc..

Power ON green LED
Graticule illumination ok, left to a minimum for now as not currently needed.
Advance Brilliance until I can comfortably see the trace, but only works on the second trace.

So the fault is not on the 'Y' Amplifier.

[ronbryan]

Yes, unplug the scope, put the lower amp in the top slot and the upper amp in the lower slot, then power it up.

This test is to see if there are two separate faults (i.e. shift and focus) and if the shift problem is associated with one particular 'Y' amplifier.

Lack of focus on one beam may be due to mal-adjustment of the CRT controls (if you are not familiar with focus and astig controls) or it may be due to a potential divider resistor in the CRT biassing for that beam having gone high.

Ron

[notallbad]

Adjust 'Y' Shift to be sure the trace is not out of view with brilliance up high and still no trace.

Just not getting a trace at all on the first now, before it was a thick band trace.

Need to turn up brilliance very high to see just a faintish blurr, not a trace as you would expect.

Just noticed that the 'Reset' lamp is lit, it wasn't lit when I first powered it on (with the 'Y' amps reversed) but do remember seeing it on before switching it off last night, sorry should have mentioned that.

P.S. All controls have been adjusted according to the manual for 'First Time Operation'.

[ronbryan]

It seems that the timebase is not being triggered. Try feeding the calibrator signal into both amplifiers, set to about 1V/cm. If still no sweep (trace), ensure that 'Stability' is fully clockwise and select trigger origin to be from the other channel.

I have never seen a TD42 timebase, which I presume you have, but on most scopes the 'Reset' lamp is normally on when single shot mode is selected and the scope is waiting for a trigger pulse. Ensure that the slide switch is set to 'Normal' and that there are calibrator inputs to both of the 'Y' amps as detailed above. Then if the scope is waiting for a trigger it should get one and the timebase should start sweeping and give a trace.

Ron

[notallbad]

OK, so Volts/cm set to 1 volt on both amplifiers
Stability fully clockwise
Trigger out set to Y2

Single shot mode not selected, normal selected.

The probes are connected to Output High on both amplifiers, do the gnd clips need to be connected anywhere? There is a trace signal on the 2nd amp but still nothing on the 1st, no change when probes connected to the CAL connectors.

Thanks for your help, it is appreciated.

[ronbryan]

You can clip the probe ground to the chrome plug-in retaining screw near the 'Cal' output if you like, but I don't think it matters very much at this stage.

So having exchanged the 'Y' amplifiers, is it correct that the fault has not moved and remains with the 'Upper' trace (as written on the corresponding brightness control), but now the 'Upper' trace has disappeared, rather than just being out of focus?

Are the 'Y' amplifiers both Type A?

Ron

[notallbad]

Yes that is correct.

And yes Amplifiers are both Type A.

So swapped the Amplifiers back around and now there are 2 traces shown and brilliance works on both but 'Y' Shift not working on upper amp.

The upper trace as also not as a defined trace as the lower,
lower trace is a dot
upper trace is a vertical line

[ronbryan]

Does adjusting the focus or astig control do anything on the upper trace now?

Does operating the x10 x1 gain push-button controls a few times change anything?

With regard to the Y shift problem, there is no way to work on the Y amp when it's installed in the main chassis. If you remove the top Y amp, you could take off the covers and look around for burnt or open circuit resistors, valves gone to air etc. Other suspects are the peaking chokes (inductors) L21, L22, L23, L24, L25, L26 which should be checked for continuity.

Ron

[notallbad]

Not sure that the focus does anything but the Astig certainly does.
Toggling between the Y Gain X10 X1 does nothing to the trace. The switching between the 2 does not seem as smooth as the Lower Amplifier Y Gain push buttons.

Shall do those visual checks and take continuity readings.

Just to confirm, I thought we had established that the Amplifier Type A was OK?
Or did I miss something?

Can I switch both Y1's and Y2's on the CRT to eliminate the fault being in the CRT tube?

[notallbad]

Having looked in more detail I don't think its possible to swap Y1 and Y2 CRT connections.

However having checked the input power to the upper and lower Y amps finds this:
Look good
Pin 7 - HT1 to lower Y Amp 290v
Pin 2 - HT2 to lower Y Amp 230v
Look not so good
Pin 7 - HT1 to upper Y Amp 380v
Pin 2 - HT2 to upper Y Amp 0v

Should be 380v before R412 so the fault must be around C411, C412, R412, R413.

[ronbryan]

I expect you've found it by now, but R413 is one section of the large 40W power resistor located towards the rear of the tube, on the left hand side looking from the front.

Ron