CRT Repair - Sun OCS Tech 80 Car Diagnostic Computer (1990) - Page 1
Forum section: electronics / repair

author: Groombridge
author_rank: Newbie
timestamp: September 15, 2015, 12:13:26 pm
content: Hi guys,I have an old Opel (GM) diagnostic computer from the early 90's that needs repair. It was originally working after being taken out of storage for 20 years but one morning the damp must have gotten to it, the anode started letting the smoke out.The anode lead was sent to be repaired but after installing it again, the CRT wouldn't work. I think it might be the connection to the line output transformer but I can't be sure.In true automotive fashion, there is no service manual or information on the unit online.The anode cap also wasn't originally sealed onto the back of the screen.I'm in the mechanical engineering side of things so I've only learned the basic operation of a CRT. Any help is greatly appriciated.Back of the CRT:Transformer and anode lead:That black stuff on the wire is grease.Anode lead:There is continuity between both wires on the anode, can someone tell me if that's right or wrong?Working Screen:The unit:Surface rust on the bottom. No electronics down there, just a storage cabinet.

author: Quarlo Klobrigney
author_rank: Super Contributor
timestamp: September 15, 2015, 12:45:09 pm
content: Both wires? You mean the green and the anode cap? That would be wrong. Where exactly is the smoke coming from? Is it the yoke, (the copper doughnut on the CRT neck) or the flyback assmy (where the red ring plugs in) then it's done unless you can find a sub.EDIT how is the video coming in to the chassis? If it's normal video, then you swap the whole mess for a LCD.

author: Groombridge
author_rank: Newbie
timestamp: September 15, 2015, 12:55:22 pm
content: There is continuity between white wire and the blue wire with the spade connector.The smoke was coming from the connection between the anode cap and the yoke. It was sent to be repaired but the screen hasn't turned on again since.There is no more smoke coming from the anode after trying to boot the computer with the repaired cable.

author: Quarlo Klobrigney
author_rank: Super Contributor
timestamp: September 15, 2015, 01:04:04 pm
content: Sorry blue wire. That would be wrong as it is most likely a ground. By that result it should have either taken out a fuse or a fusible resistor on the board. The yoke could be damaged by the arcing to it. First check for the fuses, I will be here all day, and happy to help.OOPS: open that blue wire shrink wrap and check for shorts.Also: was that yellow block always on the Anode lead? I also see what looks like slices in the gray Anode lead. This is a no-no. HV insulation must be completely intact with no cuts.Quote from: Groombridge on September 15, 2015, 12:55:22 pm

author: bktemp
author_rank: Super Contributor
timestamp: September 15, 2015, 01:16:10 pm
content: It looks like the blue wire is going into the yellow block next to the anode cap.This could be either a resistor or a capacitor or both. High voltage film capacitors fail often after many years because of moisture and aging of the dielectrics. They start to arc over (this produces smoke) and this results in a shorted capacitor.

author: Quarlo Klobrigney
author_rank: Super Contributor
timestamp: September 15, 2015, 01:23:30 pm
content: What the Kosacks who built the bloody thing never heard of Aquadag and grounding leaf springs? Why include a cap in a block thing? I have never seen this in all my years of servicing. Maybe its a Euro thing, but then I have worked on many a Philips. If it is a bleeder resistor, why?Quote from: bktemp on September 15, 2015, 01:16:10 pm

author: PA0PBZ
author_rank: Super Contributor
timestamp: September 15, 2015, 01:42:44 pm
content: The yellow block must be a cascade, and it needs a ground to work. Please measure the conductivity between the white and blue wire a bit more precise, both ways and report back.

author: Groombridge
author_rank: Newbie
timestamp: September 15, 2015, 01:56:23 pm
content: The Blue lead does connect to the earth, the blue wire goes all the way into the anode cap. I've checked all the fuses and there's no resistance in them.The yellow block is from the repair, it's not original. There are white zip ties along the grey cable if that's what you thought looked like cuts?Quote from: Quarlo Klobrigney on September 15, 2015, 01:04:04 pm

author: Quarlo Klobrigney
author_rank: Super Contributor
timestamp: September 15, 2015, 01:58:01 pm
content: No, not the tywrap circle way but the long way unless that's printing. The photo is low-res.

author: bktemp
author_rank: Super Contributor
timestamp: September 15, 2015, 01:59:53 pm
content: I doubt it is a cascade. The transformer looks like a DST.I have found a similar looking DST + cable from an old TV and measured the block: At least this block has no capacitor it is only a 170Mohm bleeder.It is probably not really necessary for operation, most likely a safety feature for discharging the high voltage when the unit is switched off.Maybe it arced over and therfore they simply bodged the block around it?

author: Groombridge
author_rank: Newbie
timestamp: September 15, 2015, 02:07:22 pm
content: Ah, yes there is writing on the side of the cable.It's not a cascade, the block is oversized to what's inside it.Would trying to boot it with the earth on the anode disconnected be worth a try or harmful?

author: Quarlo Klobrigney
author_rank: Super Contributor
timestamp: September 15, 2015, 02:10:47 pm
content: Got it now that you said it.As far as de-earthing the blue wire, what exactly is in the yellow block? If it's just a connection to repair a break, then yes you may disconnect it, if the the blue wire truly runs directly to earth.Quote from: Groombridge on September 15, 2015, 02:07:22 pm

author: Groombridge
author_rank: Newbie
timestamp: September 15, 2015, 02:19:36 pm
content: It was to repair a break, there was buzzing and smoke coming from the joint to the anode cap.I don't know myself if the anode cap should be connected to the earth or if it's a result of the arking.Quote from: Quarlo Klobrigney on September 15, 2015, 02:10:47 pm

author: Quarlo Klobrigney
author_rank: Super Contributor
timestamp: September 15, 2015, 02:25:13 pm
content: I am still confused. What was there before the yellow block anything? Was it added after? You have to answer as I am in the dark.

author: timb
author_rank: Super Contributor
timestamp: September 15, 2015, 02:41:43 pm
content: You might try searching eBay for GM diagnostic computers; I've seen them floating around but I can't recall the models. Anyway, if you find a unit that looks similar you might be able to find a service manual online that would be applicable to your model. In true GM fashion, I'd bet that Opel didn't have a special version built for them, but instead it's the same as the US unit possibly with just a different ROM set.Sent from my Tablet

author: Groombridge
author_rank: Newbie
timestamp: September 15, 2015, 03:11:34 pm
content: There originally was a round black piece of potting material in the place of the yellow block but it burnt up. I'll have to ask what's in the yellow block since the repair.It is a unit adapted for Opel, the manufacturer Sun is owned by Snap-On. I've found some information on a similar model "Sun MCS 2000SL", it uses a Motorola screen though, everything else seems similar on the inside.

author: timb
author_rank: Super Contributor
timestamp: September 15, 2015, 03:43:24 pm
content: Ah yes, that's right, Snap-on made a lot of these systems. The name was on the tip of my tongue!Sent from my Tablet

author: Quarlo Klobrigney
author_rank: Super Contributor
timestamp: September 15, 2015, 03:56:39 pm
content: I thought you had gotten ZZappedBut the question rolled over to a new page. I would say try to leave theBluewire off of earth and see what happens. Perhaps wrap it around the HT wire out of the way so it can't arc over to anything.BTW I used to see a lot of these units branded as Sun back in the day when I used to bring the car in to the mechanic.

author: Groombridge
author_rank: Newbie
timestamp: September 15, 2015, 05:44:47 pm
content: I keep a good distance when troubleshooting something that reaches kV's haha.I'll have to give it a shot tomorrow, I'll let you know how it goes!Thanks for the help so far guys!