Tempest board problem - works but image is pushed in on left side

wolfeel

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Tempest board problem - works but image is pushed in on left side

So I am trying to get another Tempest board up and running. I recapped the PCB board and it works, but the image is pushed in on the left side. If you imagine the screen image as a pane of glass being held it looks like the left side is pushed back farther (towards the back of the tube) than the right. The right side looks normal. All the vectors look good, just the image to the left of the Y axis is pushed in. Make sense? I tried adjusting the image with the PCB pots and can't get it to go away and look normal. It was working great before, but when I went to burn test it for several hours the current problem came up. Tested in another know good cabinet/monitor with the same results so I know it is a board issue. Any thoughts?
 

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Here are some more pics.
 

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I did a quick check of the POTS on the board a bit ago, but perhaps I will take a closer look. Bump for any help.
 
I am thinking it is an issue with the X circuitry, specifically the -X side. I will have to look at the schematics and do some probing.
 
It could be something in the feedback path for the pincushion circuitry. Maybe a small diode or cap on one leg of the signal?

Also, not sure if that is the 'X' circuitry or not since the monitor is vertical for Tempest.
 
It could be something in the feedback path for the pincushion circuitry. Maybe a small diode or cap on one leg of the signal?

Also, not sure if that is the 'X' circuitry or not since the monitor is vertical for Tempest.

i think it's y circuitry as far as the board goes, but x as far as the monitor is concerned. (when you're working on them.) read that in the 6100 faq.
 
If it's in X TL082 at D/E12 or A11, also can be a bad MC1495 at C12. Use an Oscope to see which output is offset below zero.
 
Also, not sure if that is the 'X' circuitry or not since the monitor is vertical for Tempest.

i think it's y circuitry as far as the board goes, but x as far as the monitor is concerned. (when you're working on them.) read that in the 6100 faq.

I am thinking the X side since when I move the X pot on the board I can compress and expand the screen image in the area where the image is pushed in (the left side of the image as you view it running and in the cab). Am I thinking correct?

If it's in X TL082 at D/E12 or A11, also can be a bad MC1495 at C12. Use an Oscope to see which output is offset below zero.

Thanks for the tips! I am going to dig this old thread up and see if I can fix this board. "Use an Oscope to see which output is offset below zero." This makes sense...no just need to get the Oscope out and start probing.
 
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The outputs put out a plus and minus voltage. This means the voltage swings above and below zero fairly equally, or should. When it doesn't and one swings more below zero you've found the problem.
 
I am not real savvy with the oscilloscope so I tried shot gunning a chip. I changed out the TL082 at D/E 12 with no change. Over the past day I have been getting familiar with my O-scope and watching some videos so I can actually use it. :) I think I am figuring out how to set the trigger correctly.

Next I will be checking the outputs on the TL082's in the X and Y sections and the MC1495L's.

If I read the data sheets correctly the TL082's have outputs at pins 1 & 7. The MC1495L's output at pins 2 and 14. I am guessing the waveforms are not going to look clean like a sine wave but will be a little more garbled. I am guessing I will be looking for the "pattern" that is shifted more below the zero line as Talon2000 suggested.
 
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tiki-download_file.php


Something like this for X

tiki-download_file.php

Something like this for Y
 
Had a setback. It started playing blind. Nothing in test mode. Found-15 not showing anything. Replaced VR1 (7915). It started to display but only in one quadrant and just several lines. Checked the -15V test point and still nothing. Checked point "W" at harness plug and got -22V. Checked the voltages on the negative side of caps C58, 56 and 60. C58 & 56 showed -22V. Found negative side of cap C60 just over 0 volts. Replaced C60 with no change. the "O" leg of VR1 (7915) shows -23.85V, the "I" leg shows 0 volts, the "C" leg shows just above 0 volts (.6). From left leg to right I get: Just over 0 V, -23.85V, 0 V.

I tried replacing VR1 (7915) again with no change.
 

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Had a setback. It started playing blind. Nothing in test mode. Found-15 not showing anything. Replaced VR1 (7915). It started to display but only in one quadrant and just several lines. Checked the -15V test point and still nothing. Checked point "W" at harness plug and got -22V. Checked the voltages on the negative side of caps C58, 56 and 60. C58 & 56 showed -22V. Found negative side of cap C60 just over 0 volts. Replaced C60 with no change. the "O" leg of VR1 (7915) shows -23.85V, the "I" leg shows 0 volts, the "C" leg shows just above 0 volts (.6). I tried replacing VR1 (7915) again with no change.

???

How is the Output leg showing -23.85v and the Input leg showing 0?

You sure about that? How is the Output higher than the input? You have something miswired or shorted if that's the case.

The 7815 (Positive regulator) pinout is Input Ground Output
The 7915 (Negative regulator) pinout is Ground Input Output
 
You sure about that? How is the Output higher than the input? You have something miswired or shorted if that's the case.

I think you are right...I probably miss worded it.

Here is a picture of VR1. From left leg to right I get: Just over 0 V, -23.85V, 0 V.

The data sheet says the left leg is Ground, then input, then output.
 

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Left leg to middle leg = -23.4V
Left leg to right leg = .41 V

Makes me think that VR1 is faulty. ??? VR1 is also getting real hot. I just metered the VR1 that I pulled and it tests good.
 

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Take the regulator out of the circuit and measure resistance from pin 3 to ground. If the regulator is getting hot then you probably have either have a bad regulator or a short somewhere on the circuit it is feeding.

RJ
 
HOLY SHIT dude!

Look at that cap in the pic... a radial cap with legs spread wide to fit where an axial cap was... PUT SOME DAMN HEAT SHRINK TUBING ON IT! That'll short for sure if you bump it.
 
Take the regulator out of the circuit and measure resistance from pin 3 to ground. If the regulator is getting hot then you probably have either have a bad regulator or a short somewhere on the circuit it is feeding.

RJ

Thanks for the tip...I'll start looking around. I am thinking that it must be a short somewhere on the circuit it is feeding (like you mentioned) since the one I pulled before that had exhibited the same problem and then tested fine out of circuit... and everything up stream seams to look OK.

HOLY SHIT dude!

Look at that cap in the pic... a radial cap with legs spread wide to fit where an axial cap was... PUT SOME DAMN HEAT SHRINK TUBING ON IT! That'll short for sure if you bump it.

It is just temporary. I pulled the old one (which was relatively new) thinking I had a problem with it...and to rule it out. I did not have an axial on hand.
 
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