Telequipment DM64 repair - Page 1
Forum section: electronics / testgear

author: bifferos
author_rank: Regular Contributor
timestamp: July 04, 2021, 11:54:07 am
content: I got one of these for free, and it looks pretty good. I got a clean trace and it's triggering nicely on both channels. The PSU caps look in good condition as well.I Downloaded the manual:http://www.kevinchant.com/uploads/7/1/0/8/7108231/telequipment_dm64.pdfOnly problem is the trace starts in the middle of the screen, so I have effectively only 50% of the display.I played around with some of the presets involved in the X amplifier calibration and influenced the timebase a little but I didn't find anything in the manual suggesting X start position. I could have missed something. In any case I find it hard to believe the thing would have adjusted itself so far out so I suspect it's something more than just a re-cal needed.Any advice? I'm tempted to just ditch it as I have a Rigol 1052E (hacked to 100MHz) already, so a 10MHz scope is a little superfluous but I hate getting rid of working kit.

author: tggzzz
author_rank: Super Contributor
timestamp: July 04, 2021, 12:16:18 pm
content: Always start by checking the PSU rail voltages and ripple.A picture would help.How does moving the x-position control affect the display?

author: Andrew_Debbie
author_rank: Frequent Contributor
timestamp: July 04, 2021, 12:24:14 pm
content: I doubt it is calibration. Maybe start with capactiors X-Axis or power supply. I haven't looked at the schematic, but at least you have it.If you decide to abandon the repair and happen to live in North Wales, send me a message. I doubt it is worth posting, but I'd be able to come collect it and make a small donation(Not sure what is allowed here - mod can delete if this violates forum rules)

author: Kleinstein
author_rank: Super Contributor
timestamp: July 04, 2021, 12:25:39 pm
content: The scope is no longer really a practical test instrument, more like an antique part worth keeping for the old days technology, like an old timer car.It looks like an old storage tube. So no DSO, but analog storage in the tube itself.There is a knob to adjust the x position (to the right from the trigger level).If really far off, so one can not center it, there may be a defect, like a half broken X-amplifier, missing one of the ouput signals.Is the horizontal time base still right, or maybe to slow by about a factor of 2.With at least much if the schematics and not too many special parts, this scipe looks still repairable.

author: bifferos
author_rank: Regular Contributor
timestamp: July 04, 2021, 12:50:04 pm
content: Quote from: tggzzz on July 04, 2021, 12:16:18 pmI'm not sure a picture will help much, but I've added it here.Adjusting x-position will move it off the screen to the right, but it won't move it any further left.

author: bifferos
author_rank: Regular Contributor
timestamp: July 04, 2021, 12:52:35 pm
content: Quote from: Andrew_Debbie on July 04, 2021, 12:24:14 pmI'm not far from Oxford, so that's out, but thanks for the offer.

author: bifferos
author_rank: Regular Contributor
timestamp: July 04, 2021, 12:56:36 pm
content: I think the posts here confirm my suspicions, that it's not a simple adjustment, and much as I'd like to repair it there are so many other interesting projects I could be spending my time on I will probably give it a miss.thanks everyone.

author: Andrew_Debbie
author_rank: Frequent Contributor
timestamp: July 04, 2021, 01:27:34 pm
content: Quote from: bifferos on July 04, 2021, 12:52:35 pmOh well. I've got an older '100 mile' electric car. A day trip from Anglsey to Oxford is entirely possible but not practical.I had averyquick look at the schematic.I'd start by checking all the power supplies, but espeically the ones that feed to figure 6. After that I'd check or replace all the capacitors in Fig 6. In my very limited experice with old 'scopes it is often a bad cap.It isn't the blanking, you've got a display . . .

author: bifferos
author_rank: Regular Contributor
timestamp: July 04, 2021, 03:52:40 pm
content: I'm feeling a bit silly now. Just as I was going to put the covers back on I realised there was this loose lead. I'm not sure how it came off because it had a fair amount of grip, but yeah, pushed it back on (with the power off!) and it's now right as rain.

author: Andrew_Debbie
author_rank: Frequent Contributor
timestamp: July 04, 2021, 03:54:35 pm
content: Good! I didn't want it to end up in the tip.

author: Andrew_Debbie
author_rank: Frequent Contributor
timestamp: July 04, 2021, 03:56:55 pm
content: Quote from: bifferos on July 04, 2021, 03:52:40 pmA previous owner. . .