Bottom half of wg6100 screen collapsed on Tempest

komodo

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Okay, I've Googled this issue and found little to help me. I'll give you a little background on the monitor and where I am at.

Monitor was repaired by me about 2 months ago. Basically replaced some bad caps and parts in the Low Voltage section along with a few transistors. Deflection board is a 314 model. Monitor was installed in a Tempest but apparently whoever did the installing bent some of the tabs on the bottom of the monitor frame where the transistor leads attach and shorted out the power and some X-side transistors. I replaced all of those, repaired the broken wire, replaced some parts in the LV section again and have the monitor working fine now.......

Except........, I cannot get an image on the bottom half of the screen when you play Tempest on it. The board set is tested good so it is definitely the monitor. Realize of course that the monitor is mounted vertically so if you were to look at it horizontally, there is only the RH side of the screen visible. You can tell the LH side has collapsed to the middle. I have checked, and rechecked and even subbed in the TO3 (bottlecap)transistors even though they tested good with no results. I have checked for cold solder joints on the header pins for the X, Y, and power attachment points on the deflection board and cleaned and reflowed each of them. I have checked for continuity from the transistors all the way to the deflection board. I pulled and tested Q702, Q704, and all the diodes and resistors on that part of the X circuit.

Am I hunting in the wrong area? If you read the FAQ, it describes the area each transistor covers. In order to have the failure I am experiencing, it would require 2 of the bottlecap transistors to fail. That is why I looked at the Negative side of the X circuit. I have read and reread the FAQ and think there my be a type in the section covering the transistors but it may also be that I am reading the schematic incorrectly. It is my understanding that Q706 is responsible for the negative X (LH) side of the image and Q705 is responsible for the positive X (RH). This of course is when viewing the monitor mounted in a horizontal position. Because Tempest is a vertical mount, the transistors still work the same part of the monitor even though the axis are swapped, is that correct. Or, do I need to start troubleshooting the Minus Y-side of the Deflection board in order to find the reason why I have no image on the screen?

Anyone that can shed a little light on this will probably assist countless others. I have never had this much difficulty isolating a problem like this. It is usually a bad bottlecap transistor and poof, I'm done. I will say again, all these transistors are good/new/tested numerous times. While I have repaired a lot of these monitors, I am still learning and still have along way to go in my understanding of these.

I look forward to some interesting discussion.
 
Reflow the solder on the sockets on all 6 of the chassis mounted transistors. Should cure your prob.

391ad686.jpg


Andrew
 
All the voltages are good on the trannies and I did reflow the solder on the transistors as they had dorked up one of them pretty bad. I may go back and redo them all again. I will report back. I am all out of ideas right now. Maybe I made a cold solder joint somewhere and just don't see it.
 
Did you perhaps reverse one of those transistors? Easy to test, just swap the two transistor harnesses at the deflection board. You may have to take the board loose to let them reach. If the problem switches to the other half of the screen, the problem is with the tansistors/sockets/plugs. Could be as simple as a bad connector on the end of one of your harnesses. If the problem stays the same, it is on the deflection board and you should concentrate your efforts there.
 
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Is the picture kinda squished near the center of the screen? It could the the constant current source in the deflection circuitry. Check the signal to the bases of the output transistors to be sure its not in drive circuitry.
 
Both good ideas to help trouble shoot. Out of town right now. Will report back but will be Monday at earliest.
 
I told you on the phone it's a FUSE!!

LOL..

Pat is pretty good with vector monitors, so if he's here he is genuinely stumped, it's not often that he will over look the normal easy stuff.

Bring it over monday and I'll replace the fuse for yah.
 
Yep, it was a fuse........in my brain. Nope, it turned out to be the socket. If you look at Andrew's picture up above where he shows the re-soldered wires, you will notice the legs of the transistors poking thru the base of transistor socket. In my case, Q706 had the leg of the transistor for the white wire not making contact with the crimp portion of the socket. I had checked for continuity from the white wire standoff to the actual circuit board and there were no problems. What I needed to do was check for continuity from the leg of the transistor to the white wire. Incidentally, Andrew's socket looks worse than mine did. I guess he is getting a good enough fit.

I took Mongo's advice and swapped the harness to identify the problem in the harness or socket or deflection transistors. I did manage to pop the positor loose from the deflection board but I'll fix that as well. I'm just thrilled it was a easy fix. I guess poor lighting and poor thinking kept me from finding the obvious.

I'm out of replacement sockets so I squished the "crimps" together and got it working again. Time to order more sockets. Thanks guys.
 
Glad you got it fixed. I too had to squeeze socket once to get a tight fit on a transistor.

Andrew

Resurrecting this thread to document a similar problem, but on the other half of a 6100 that I'm working on. Should be a similar problem/solution to the OP.
 

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