Sick Telequipment D83 - extracting power supply

[MrBungle]

I have a sick D83 on my hands. It appears to be the usual power supply and HT problems. PSU has masses of ripple. HT is, err, wonky as hell. Sometimes it comes up, sometimes it doesn't.

I'm going to do a blanket replacement of power supply bits first, get that stable then rebuild the HT.

Does anyone know how to get the power supply out if that is possible, without having to desolder everything?

[MotorBikeLes]

Simple, two screws (I think just 2) on the back. Pull out as it simply plugs onto the mother board. Either struggle for access, or unsolder the trailing ground wire. I have had smoothing caps fail, but not much else that I recall.
The EHT module usually just needs the strings of high value carbon resistors replacing. Later production already had this done. Typically use one suitable value VR38 for each string. The variable in the string should ideally be a cermet type not carbon.
I think I have already itemised these and posted the correct values here previously. try searching under D85, D83 or D(M)63.
Les.

[fetteler]

I'll second Les's comments and will add that I have had the top of the EHT transformer (where the terminals are mounted) go strangely leaky due to tracking between and through the laminations of the paxolin/srbp.

These D83s are great oscilloscopes

Steve.

[MrBungle]

Thanks for the tips - much appreciated. They are indeed nice scopes, one reason I jumped on this. I've actually got one mostly working one and a mostly eviscerated spare one here. Both are complete with plugins in varying degrees of repair. Also have a calibration plugin.

The mostly working one is being targeted for complete rebuild and calibration and the other will be held as a parts mule. I could probably get both working as they are complete but that would leave me with no spare parts.

Do you know if it's easy enough to replace the Paxolin strip on that? I have plenty of FR4 board lying around which should be somewhat more tolerant of HV in theory.

Both of these ones have Mullard VR37 resistors in. They are circa 1982 looking at the date codes so quite late. The caps however are in a bit of a state.

My plan is as follows:

1. Replace all the electrolytics and tropical fish caps in the PSU as they are running hot and there's some PSU ripple and some of the trops are cracked.
2. Yank the HV board out, replace all the parts, rebuild it and clean it.
3. See if the HT issues persist.
4. If they do, replace the paxolin strip on the HV transformer.
5. See if the HT issues persist.
6. If so, build a new multiplier for it.

Hopefully that'll make it last a few more years

[mhennessy]

Originally Posted by MotorBikeLes

Simple, two screws (I think just 2) on the back. Pull out as it simply plugs onto the mother board.

Definitely true for the D(M)63, but for the D83 this might not be the case. See the pictures here: https://www.vintage-radio.net/forum/...49&postcount=8

As you can see, the lower section of the rear panel is one lump of metal. This means that you have to lower the PSU PCB from the bottom of the unit, leaving the socketed power transistors bolted to the rear panel..

Unlike the D(M)63, there's no edge connector to the motherboard; it's hard-wired.

The D83 is a much harder 'scope to work on compared to the D(M)63 - perhaps later models were changed to bring them in line with the D(M)63, and if so, I'd be interested to learn more. In the meantime, I have 3 of these up in the attic, and not enough enthusiasm to do anything about them

[MrBungle]

I've just had a look at it closely and you're right. The entire unit will however separate into a top and bottom half. I thought hey I'll refurb the bottom half of the dead unit (as it has an IEC connector instead of the oblong one) and attach the other one's top and backplane. However some of the looms and mains wiring make this difficult to achieve without some major rework. I think I will attempt to service it through the bottom and sides.

I did start motivated to strip the whole thing down and rebuild it but that's wearing off pretty quickly now.

[mhennessy]

I thought the 2 halves were riveted together? Pretty sure they are in the D(M)63, but if they are screwed together in the D83, that's nice and convenient

[MrBungle]

Well it would be if they weren't also wired together

So close to perfection but so far at the same time

[MrBungle]

Attaching some photos for the sake of reference.

This is why I've been after one of these. Quite possibly the best trace out of a scope. The same humongous tube as a Tek 7603 without the very noisy vertical amps. The picture doesn't do it justice really as it's much crisper viewed through eyeballs



Power supply - will need to use Keyhole surgery on this I think:



HT:

[MotorBikeLes]

Egg on my face time. I used a D83 for quite a while, but let it go when I got an HP 1740C(?) with the same size tube. I must say I liked that HP, but it was HEAVY. Over the last few years I have had quite a few D(M)63s through my hands, and D75s, so completely forgot the PSU was rather more difficult on the D83. I was given one from here last year (Heavy carrying it on and off the ferry!), but other than a quick try, I have not had time to service it yet. That screen photo of yours Mr B is VERY impressive. Very many of the D83s are double humped by now, including the one I have here so getting a sharp trace is no longer possible. If I could get a decent tube, it would immediately replace the TEK 475A currently the "switch on" scope.
Cheers, Les.

[MrBungle]

I do like the HP 1740 scopes. I had one for a bit which was in perfect condition. I seem to be a holding pen for sick scopes. I buy 'em broken, fix them (the fun bit) and then get fed up with the sight of them and they're gone. Someone invariably gets a working scope out of my meddling and something doesn't go to the tip so life is good.



These are my 2nd and 3rd D83s. I think I paid £5 for my first one from some guy on Gumtree who didn't know what it was. I instantly regretted selling it but at the time I didn't have the space for it. I don't really now but my other half is more flexible now

With respect to the double hump, this isn't as much of a disaster as it sounds. The tube in them is a standard tektronix tube, the T7400-31 of Tektronix 7603 fame. So if you can find a dead 7603 mainframe lying around without any plugins, which is never an attractive proposition for the buyer, then there might be a good new tube for the takings. Lots of 7603's get scrapped because the power supply has gone bang or the plugins have been stolen or some knobs have been damaged. I'll let you know if I come across a tube.

My current "switch on" scope is also a Tek but a 465 which I meticulously restored. The earlier 465 and 475's are rather nice. Slightly off topic but:





I have a scope problem

[MotorBikeLes]

Mr. B, a bit more egg on face I think. The old HP I referred to was of much earlier vintage, one with tunnel diodes in the two timebases. I really can't be sure of its model number, but it did have same screen size as D83, but screen illumination was dome internally using a mesh rather like that in a storage scope. I had about four different ones of the same vintage, including a 250Mhz bandwidth jobbie with a rather unusual set of Y channel plates in the CRT (distributed transmission line I think correct description).
I have a 1703A, same series as your 1740A, but smaller display, storage tube, and internal batteries giving rather heavy portability.
Les.

[factory]

The earlier HP scope with a larger screen could be the HP 182C with a 7" CRT & 100MHz bandwidth.



The higher bandwidth version in the same series was the HP 183A/B/D with the 1830A vertical plug-in for a 250Mhz bandwidth.

David

[MrBungle]

Very nice scopes as well those ones. I had the pleasure of using one many years ago at university. It was those or a 54600 series HP. Also a damn good scope!

Quick D83 status update. I have basically done what I can only describe as a “bum transplant” and migrated the good bottom and good top halves into one working scope. During this process the power supply was refurbished and had a lot of replacement parts added as well as recalibration. This was not trivial and resulted in my living room looking like a scrap yard for several hours. I don’t recommend it. In fact it was probably the hardest repair I’ve done and I’ve done some bad ones! Had some problems with all horizontal deflection failing miserably after the transplant and planned to used my tek 465 to debug it. Unfortunately that just blew up in my face at lunch time today with loss of triggering due to a power supply problem.

These things are sent to test us but I wish they weren’t.

So I’m now the proud owner of four broken scopes and zero working ones!

[MotorBikeLes]

Yrs, mine WAS a 182C. In fact I remembered it myself only yesterday after seeing a ref to a 180. I had a 180 and the high bandwidth 183 as well. My 182C only had a two channel Vert amp, not 4Ch as shown. Soo heavy, but a scope that could still hold its head up today. Good luck with the repairs Mr. B, you will get there. As you say, these things are sent to try us, and we are usually found guilty! Les.

[factory]

That was a picture I had saved (not mine), neither the HP 182 or HP 183 seem very common and of course lots of different specification plug-ins were available.

David