G08 problems continued..

mcandrewsoun

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Couple of questions... The game is eliminator.. Using my scope in XY mode, I can see the game playing..

1. Should I be able to see the Game playing using the Scope on the Monitor deflection outputs, or does the G08 modify the signal?
2. I get output signal (measured at the Fuses) with the deflection transistors connected, and the yoke disconnected. When I connect the yoke, the deflection goes to almost 0.

All the transistors meter out ok.. It only affects Q601/Q701 and higher.. Q600/700 seem unaffected.

Andrew
 
If I recall, the collectors of those output transistors are tied to the +/- voltage rails (about 65V). The bases are driven by a deflection signal that is very close to the same rail- so if you look at the C-B junction you'll see part of a signal.

I used to look at EVERYTHING with the yoke unplugged, and then when it looked like deflection was making it all the way, plug it in.

Again, hard to say without having one in front of me- but I don't think you get any HV without the yoke plugged up. There are some 'sense' resistors in that circuit that feed back to the HV unit and enable the HV.

I'd say you're getting deflection all the way. If the output transistors were shot, you'd probably be getting smoke from the paddle boards.

Measure all your inputs on the HV connector. I see lots of bad header joints there.

Also, if the deflection is working, I think you get the chatter in the yoke even if the HV is off. If so, it might be worth tweaking the pots on the HV cage to see if you can get some output.

You get no heater output if there's no HV.

Couple of questions... The game is eliminator.. Using my scope in XY mode, I can see the game playing..

1. Should I be able to see the Game playing using the Scope on the Monitor deflection outputs, or does the G08 modify the signal?
2. I get output signal (measured at the Fuses) with the deflection transistors connected, and the yoke disconnected. When I connect the yoke, the deflection goes to almost 0.

All the transistors meter out ok.. It only affects Q601/Q701 and higher.. Q600/700 seem unaffected.

Andrew
 
At this point I have the HV disconnected, so I can actually work on the board without the rats nest of wires. I can see signal on the outputs, UNTIL I plug the yoke in. Its also wierd that both X and Y go.. It think if it were a bad resistor or solder joint, Id lose X or Y. The rails seem steady at 63V. Im wondering if theres something messed up in the error correction that back feeds IC 600.

Andrew
 
update..found a bad solder connection affecting the biasing of one of the driver stages..two diode traces were shorted together..now I get a picture. However, the input protection board is hosed. when I connect I get a garbage..without it I get most of the picture, but huge. The peak to peak from the game on the h and v inputs is around 8 volts.

Is there a schematic anywhere for the input protection board? Someone did a cap kit on it, and I want to be sure they did it right (they shorted out the diode trace above, and used the 3716s in the output, so I wonder).

Also (another problem I have to debug) is that it looks like all the guns are all on all the time..everything is white, and extremly bright..brightness has little effect.

Andrew
 
Are you getting any valid signals from the RGB on the XY control board? That could cause the retrace/white lines.

Also, problems with voltages on the neck board can wash everything out too.

8V p-p may be a little much for the inputs. If I recall, the vertical in should be a lot lower than the horizontal.
 
I think most of my deflection problems are on the paddle boards. I removed the transitors that clamp down the signal to the base of driver circuits, and the screen looks fine. on both the x and y the 3906 was the culprit..now I havent figured out if its the transitor, or whats feeding the resistor. I havent messed with the neckboard yet..
 
Resolved

(After replacing all the deflection transistors with the correct ones, and a couple of the MPS U10 and MPS U60s)

Problem 1. Screen way off center and clipped just past mid screen Solder bridge between two diodes on the driver circuit.

Problem 2. Clipping on H axis at 80%. I had inadvertantly replaced one of the .15 resistors with a .5 resistors. This created a larger then expected voltage across the base of the curent protection circuit (only on the positive side) which in essence clipped the waveform.

Problem 3. All guns firing all the time. Thanks to kstillin I checked the voltages first. Problem was the 55v regulator transistor.

Problem 4. Blue gun stuck on. Driver transistor was completely not soldered in. Resoldered and good to go.


Andrew
 
Sounds like someone before you hacked this thing to hell?

Resolved as in things are working great now?
 
Sounds like someone before you hacked this thing to hell?

Resolved as in things are working great now?

While working on getting my Star Trek up and running I went thru every G08 I had and every single one of them was hacked to hell. Most of the hacks were "factory" fixes or recommended fixes but the work was incredibly sloppy. These are no fun to work on with the neck board soldered to the focus block. I put in a molex connector like one I found on one of the monitors I was trying to get running. I have a long road ahead of me.

Just wanted to say thanks to the OP for the post as this may help me in my repairs
 
Good luck with the repair!

Couple of things to keep in mind on these.

(You need a scope in XY mode to do the following)

1) I tested everything with the deflection board off the monitor, and the HV disconnected. I mainly did this because there are so many short wires going so many directions..

2) Get the thing working 1st with the yoke disconnected, then try it with the yoke. This will save fuses and output transistors! I clipped the probes on the fuses. You'll get 120v pp deflection with the Yoke off. Look for clipped signals. I tested X and Y separately by connecting one probe to the Y input on the deflection bd, and the other to the Y output to test X and reverse it for Y. You can follow the signal on the collectors of the drive transitors (heat sinks!) and also on that diode/resistor/cap that are bridged together.

3) Check and verify all the voltages. Set the DC voltage on the collector of Q600/700 (I think) to 30ish volts using the horizontal and vertical positioning pots. Thats a good place to start, and will verify that they are working correctly.

Andrew
 
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