Telequipment D83 timebase control

[BulgingCap]

I have just acquired a Telequipment D83 scope that was dumped on the council tip. It is in mint condition with a V4 and an S2a plug-in, and after spraying the pots and switches with cleaner using a hypodermic and replacing three signal transistors- BC108 and BFY51- it sprang into life. It has the crispest trace I have seen on a CRT scope.
The only issue is the plastic knob for the dual timebase has disintegrated. I understand that this is a common problem, and they all crumble eventually due to UV probably.
I cannot see an easy way to disassemble the switch to remove the remnants of the knob, and then assess whether I can make a replacement (I have a lathe).
Has anyone attempted this?
Regards, BulgingCap

[karesz*]

Hello B.C.,
do you know/checked these sites please?
Karl

[BulgingCap]

Thanks Karesz, they are interesting sites and I have bookmarked them.
I am not looking for spare parts but for info on removing the clear plastic concentric knob on the switch.

Another question while I am here:
I cannot see how the plug-ins are supposed to be secured or latched into the scope. No screws are visible, and only the friction of the edge connectors stops them falling out. I know I have missed something and am about to feel really silly!
Regards, BC

[Alistair D]

The delay knob had 2 holes on the side. You rotated the knob until the holes lined up with the holes in the fixed boss the module body. You can then insert the allen key and loosen the grub screws. Since the outer ring of the knob is now missing you will have to try one click at a time until you find the grub screws.

The module lock was a piece of plastic that screwed to the bottom of the scope and sat either side of the seam between the modules. It projected out of the front of the scope by a few cm. The idea was that you push down on the projecting part and slid the module out. On many D83s the lock broke off after a few years. A replacement can easily be formed out of a bit of spring steel.

Al

[karesz*]

Hi BC,
Dont worry with locking stability of your plug-ins; only the edge connector contacts makes enough force for lock it.
You have to set the clear TB-switch to 50usec position, than you will find 2 smoller holes on its side_yet free for plug trough your tool; than take a fine imbus key so ca 1,5mm and you have it delocked-solved...
Regards, Karl

[Alistair D]

With only the knob boss remaining it will be difficult to know what range the control is set to.

I have just had a look at an old boss that was kicking around the workshop. The grub screws sit below the level of the outer ring of plastic. You should be able to feel the allen key drop into the hollow when one of the grub screw holes lines up with the hole in the fixed boss. If you are lucky both the grub screws will line up otherwise rotate the delayed sweep control till the next one is found.

Al

[MotorBikeLes]

The two units are held in as already said by the plastic clip. you can see it in the photo of Alistair's 'scope.
The D75 was essentially the same, but sold as a portable, with the vert and TB units fixed, not intended for swopping. They were held in position by two small screws, front and rear, through the frame. If you examine your plug ins, the holes should be present, and if you wanted, you could carefully drill holes trough the bottom of the chassis to line up, so make them un-able to "move without permission".
I once bought a virtually unused D75 (it had a fault, hence not used) and the trace on that was BRIGHT, the only one I ever saw (and owned) which was brighter (it would light up the room) was a 453A. That came from a big firm, and had "belonged" to the departmental boss; obviously he never used it nor let anybody else touch it. I have had some fairly bright D83s, and a couple of "double humped ones, but never a "light up the room" display. I have on on its way here, courtesy of this forum, perhaps that will be BRIGHT. It will get top position if it is.
Les.

[Alistair D]

Have another look at the picture of my scope. About a quarter of the way down you will see a BNC plug with a keyring hanging from it. That is the Alistair D(yet to be patented) module puller. The modules on this scope seem to be a bit tighter fit than on some of my previous scopes and I do swap the V3 module with a V4 from time to time. A few minutes with an empty BNC plug a bit of TCW and spare key ring and hey presto. It works very well too

Al

[BulgingCap]

Many thanks for the replies everyone, I am very grateful, especially for the pics, Al.
I can now see what I am up against and it is nowhere near as bad as I had feared- I was thinking that the knob had splines or some such but it looks a very simple job to machine a new one possibly based on the original metal core. I may try to cast clear resin onto it in a mould then machine it to shape.
I will have to be careful turning the remains as they are crumbling badly (and stink really bad for some reason!) I may try to release the indent ratchet to ease things.

One more query- I have the alloy scale sitting behind the remains of the clear plastic. It is completely loose so I assume that it must originally have been been glued onto the grey boss.
Regards, BC

[Alistair D]

Yes the dial should be glued to the grey boss. On the one scope I have seen the dial was made of back painted celluloid? In that case the type glue is important as the solvent may damage it. Double sided sticky tape may be the way to go.

Al

[BulgingCap]

Thanks again all- I have removed the remains of the plastic knob and produced a drawing. I will machine a mould from wax tomorrow and pour a clear resin item, with the alloy insert, to machine to size (It is a difficult shape to machine from a perspex bar, and I don't have anything that size anyway...)
I had a close call with the scale- I cleaned the glue from the grey boss then attacked the scale without really looking well enough. It is clear plastic with print on the rear- Aaargh!
The whole timebase knob design is not good at all- it should be a much bigger diameter for clarity of 23 detents.
The only fault that I can now see is that the scope will not sync on Ch2. Ch1 and ALT are fine so this doesn't seem to be a major problem looking at the circuit diagram.
I have a Cossor CDU150 so will see how they compare ergonomically.
BC

[MrBungle]

Interested in this as a former D83 owner - paid £10 for mine from gumtree. The timebase knob on mine had fogged up and cracked but not completely disintegrated. Thoroughly regret selling that scope. I keep bidding on them on eBay as well but apparently I'm too cheap!

As for brightness, mine was very bright. The only thing I've had brighter is my Tek 475. The Tek 475 doesn't go near it for crispness. My Philips PM3217 is about the same.

Think I just realised I have a scope collecting problem

[Alistair D]

Originally Posted by MrBungle

Think I just realised I have a scope collecting problem

I think I am cured now.

The only scope related item I am looking for is a very rare V2 module to go with the DM63 pictured above.

Al

[BulgingCap]

I have managed to mould a new timebase knob and am very pleased with the result. It was a pleasant job, for a change.
I machined a mould from the remains of a large candle but not only did I make an uncharacteristic and huge error with one dimension- that even a badly trained chimp could have pointed out- but I found that this type of candle is fabricated by pouring wax into a mould containing a square small candle with wick. This leaves a square fault line that coincided with a machining dimension. The wick in the centre was also a nuisance when I drilled the 6mm hole as it grabbed and tore.
The worst confession is that I cast the knob before I realised the error, but it was good practice !
The soft wax was not perfect for gripping in a lathe chuck as it seemed to 'relax' if left for a while.
I ended up melting the candle into an aerosol top and machining the mould in the top. The plastic top was easier to grip in the 3 jaw chuck.
For a lathe tool I used an El Cheapo 'jeweller's screwdriver' with a bit of relief ground on the blade.
I filled the two threaded holes in the alloy boss with plasticene to keep out the resin, and formed a pillar projecting from each to make it easier to drill a hole for the grub screws and Allen key (impulse key)
I turned down a pencil (Good old Ikea...) to thread the alloy boss onto and locate it in the mould, then poured the resin up to a meniscus. I was worried about the exothermic reaction but mixed in the minimum accellerator. The wax was melted out by immersing the wax in medium hot water whereupon it floated to the top. I left it to set and repeated a few times to get rid of the last of the wax.
In the pictures the top face of the knob has been polished with Brasso to a shine, and the opposite side of the 'window' needs a slight polish with a bit of rag on a stick.
At present I am drawing a new scale to print before I fit the knob.
Regards, BC

[MrBungle]

Brilliant work. Looks really good.

[BulgingCap]

Just a quick query regarding the notorious HV caps in the EHT circuit of the D83.
I switched on the scope a few days ago and... nowt !
The EHT circuit was not oscillating so no EHT. I traced it to one of the black EFCO 20nF 5kV caps (C307) which had transmogrified into a 4k resistor.
The cap is listed as a polyester type. I cannot find this type at this voltage so would it be acceptable to order a ceramic type?
I intend to change both of the 20nF cathode filter caps.
The waxy-looking 10nF 4kV C306 and C309 in the grid supply are listed as ceramic type and I will swap those too while I am in there.
Removing PC129 is not an easy job, and I cannot imagine how it was assembled on production nor how I will resolder the wires- some of which are soldered to the 'eyelets' from one side of the PCB and others to the 'eyelets' from t'other side.
I may as well replace the Paxolin on the transformer whilst I am in there.
I assume that rivet 'turret lugs' would be used through a piece of plain glass board? If such things are still available.
I have attached a schematic but I really intended this for MB Les and/or WME Bill as I'm sure they will have the circuit in their heads.
Regards, BC

[MotorBikeLes]

Circuit in my head, not likely. I do have a D83 to look at when I get time, but it is 30 years since I was a bit more familiar with them. I MAY have some suitable caps, but without looking inside first, not sure. I don't see why an HV ceramic should not be OK. TQ did use them in some"non-modular" EHT multipliers at one time. While you are in there, be sure to root out all the green and blue resistors (ie, greater than 1 Mohm) and replace with VR38 types. Nine such in early boards, replaced by just four higher value VR38s. R315 pot should be a cermet type, not carbon.
Maybe Bill has circuit in his head?
Les.

[MrBungle]

Just did the HT on my D83 (pre knackering myself - still not sorted - grr!). The board isn’t that difficult to get out. The only problem I had was with the diodes disintegrating. I bought ceramic HV discs from hvstuff.com in the end and Vishay VR resistors from Farnell. You can’t get 20nF caps so I bought 10nF ones and soldered them in parallel. Pre-resistor change it looked like this:



Take the transformer out first though. Makes it a lot easier.

Watch out for the blue wrapped coax there. It’s got solder leeched up it so I ended up snapping the end off which added another 45 mins to reworking it.

I’ve lost intensity control now unfortunately though and am off feet for a bit so can’t even lift the thing up at the moment.

[BulgingCap]

Thanks Mr Bungle and Les.
The resistors have been changed for the 'blue glaze' type at some point in the past- the empty pads have solder on them so (pre-wave soldering) it must originally have had the string of carbon resistors.
I have ordered the ceramic caps, and some turret lugs as I seem to have lost the few that I had (still got plenty of Vero pins...) Hopefully the instrument will be back in use in a few weeks.
BC