DM63 Scope Memory Problem

[geertcor]

Hello,
anybody did hear this problem on a dm 63, when you turn it on its like the storage board works the whole time, the light on the background is to bright and you can not adjust it with the brightnes controle ,the signal is there but not so clear especialy when the time base is hi,the focus is not working.
anybody an idea?

[maninashed]

The DM63 is the storage version of the Telequipment D83. I would advise that the first job will be to fix the basic functions of the scope. You will find that the focus control resistor chain is on the eht oscillator pcb, and its not an easy thing to work on as access is very difficult. If you are skilled, remove the pcb to work on it, and obtain the circuit diagram off the internet. The diagram for the D83 will be fine for this job. The resistors in the focus chain will be open. Its a common problem. You must use high voltage rated resistors in this position as normal resistors are only rated at 300v max. While you have the board out replace the feedback control resistors and the ones in the brightness circuit, it will save you a lot of work in the future.
Bill

[geertcor]

thanks, for the advice,i wil look in to it and put the result here.
geert

[WME_bill]

DM63. Could I endorse what Bill "Maninashed" says about this unit. Get the EHT and Focus/Intensity working before worrying about the Storage. Those resistors in the EHT chain always go - a false saving when originally made. Replace with metal glaze, the light blue ones as made by Philips. The exact values are not important, just the ratio either side of the focus control. Same for the chain across the tube grid supply.
Do not follow the D83 EHT power supply diagram too literally though, as it is not exactly the same as the DM63. The D75 and D83 were identical. The non storage version of the DM63 was the D63, with a split beam tube specially made by Philips (contract type 95470) to be electrically and mechanically identical to the English Electric E720B, except no storage.
While experimenting, you can use normal metal oxide or carbon resistors for the high voltage chains just to prove what is faulty, but recognise that they will change in value over a few hours/weeks, and so do not offer a lasting repair. I have done that while waiting for the correct parts to enable me to pin down the particular part that is faulty.
The Intensity control operates via some switches on the Storage board through to the Bright-up circuit, and I always suspect the transistors there. They operate under highish voltages, and seem to fail.
You will need the proper manual to understand the storage circuit. It you are stuck, I can scan my copy, though Bill (Maninashed) might already have one available. wme_bill m0wpn

[mhennessy]

Yes, I've had exactly that fault too. It was an open-circuit R325, but as has been said, any one of them can cause problems. As that PCB is such a pain to get at, it's worth changing them all once it's out. And the electrolytics...

The schematic has been posted here: https://www.vintage-radio.net/forum/...ad.php?t=74595 (see post #9)

Good luck!

Mark

[maninashed]

Mark, that was an extremely good article on your website and very well written. It helped me some years ago now when I tackled one of those myself. Quite a nice scope when working well. I have found that the main killer of these scopes is a breakdown of the insulation of the paxolin tag board on the eht oscillator transformer. It breaks down between the laminations of the paxolin, causing a pungent smell, and can be fixed by inserting some porcelain or nylon pass-through insulators. The main problem is the delicate nature of the secondary winding wire which tends to snap off too close to the transformer for repair.
Bill

[MotorBikeLes]

A month or so ago, possibly relevant to D75, I listed all the important EHT resistors for D75, D83, D 63 and DM63, and I think I may have added TQ part numbers. The resistor types used by TQ on all later production was VR37.
Les.

[Alistair D]

My DM63 was possibly somewhere in the middle of these upgrades. The resistors in the brightness circuit were blue bodied VR37 resistors. The resistors in the focus circuit were black bodied of unknown manufacture.

geertcor, I seem to remember that failure of the focus chain did produce some background illumination as well as a de-focused trace. You may be lucky and cure both faults in one.

Al

[geertcor]

Hello all, i have the print out so now i gone replace the resistors, i hope that the two faults wil be helped.
Geert