G05-801 deflection issue

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Hi;
I have been working on this deflection PCB for quite some time and I am at the end of my rope.
When I fire up the monitor, spot killer illuminates and R620 and R720 get burning hot. I checked and are getting full voltage to the yoke, ~24v, steady on pins 1 and 4 on P702 - not good.
When I swap a known good deflection PCB, I got game, place this back in, spot kill.
I disconnected the yoke to troubleshoot, and checked for input, got it at P703 and traced it up to the pots and then I am having a problem continuing up the ladder.
Any hints on what might be causing the lack of deflection??
I checked Q704 and Q705 and have ~23v on all legs, (B-E-C).
I am going to have to pull the PCB to get access to all the transistors in the circuit.
Any help would be appreciated......
Thanks
Jeff
 
Not sure why but even though these are 2 of the exact same model deflection PCBs, the non-working has no zeners at ZD600,601,700,701 and R621 and 721 were 3.3K ohm instead of the speck'ed 6.8K ohm.........
 
Only the obvious stuff

Transistor bolts not insulated properly (If applic.)

Bad Header solder - reflow etc

Check each component 1 at a time on both boards to compare (Good board / bad board etc)
 
Dez;
That's what I am up to at this point....
I had checked all the components, now I am tracing the schems to insure all the components are indeed connected to each other, you know, one of those "hairline cracks" or something to that effect.
It's very strange and I am truly looking forward to finding this cause of my stress.....
Thanks for the response.
Jeff
 
Holy c--p!!!!!
This deflection board is driving me $%#%# crazy!!!!!

I checked all the components in the X and Y deflection circuits to insure they are within specs.

I checked that the components were connected to the following and preceding components by sounding out each and every connection!

I still get the spot killer!!!!!

There is no deflection chatter when fired up and the spot killer illuminates. If I turn up the brightness and or the contrast, I get a dot in the middle of the screen so there is in fact, no deflection and the spot killer is doing it's job.

When I swap a working deflection PCB into the chassis, the monitor fires so the problem is in fact somewhere on this board....... As I said, I checked all the components, sounded out all the connections and still have not deflection. I am at a loss at this point.

I will go through the intensity and spot kill circuits tonight but I do not think that there are the cause of the problem as there is no deflection chatter, not like I hear the chatter and still do not see the display, just a dead monitor...... This is one for the books!

Any suggestion, (with the exception of giving up) would be appreciated.

Thanks
Jeff
 
One note, I replaced the MPSU56 transistors with MPSU57. They are both 2A but the '57 is rated at 100v vs. the 80v rating of the '56.
 
Also, as the MPSU57's have a different case, I used the clip on heat sinks as opposed to bolting them onto the PCB with the original heat sinks. I checked several times to be sure and there is no electrical connection to those studs but maybe there is a mystical connection that has been broken?!?!?!?
 
Worn molex plugs?? ie pins

Holy c--p!!!!!
This deflection board is driving me $%#%# crazy!!!!!

I checked all the components in the X and Y deflection circuits to insure they are within specs.

I checked that the components were connected to the following and preceding components by sounding out each and every connection!

I still get the spot killer!!!!!

There is no deflection chatter when fired up and the spot killer illuminates. If I turn up the brightness and or the contrast, I get a dot in the middle of the screen so there is in fact, no deflection and the spot killer is doing it's job.

When I swap a working deflection PCB into the chassis, the monitor fires so the problem is in fact somewhere on this board....... As I said, I checked all the components, sounded out all the connections and still have not deflection. I am at a loss at this point.

I will go through the intensity and spot kill circuits tonight but I do not think that there are the cause of the problem as there is no deflection chatter, not like I hear the chatter and still do not see the display, just a dead monitor...... This is one for the books!

Any suggestion, (with the exception of giving up) would be appreciated.

Thanks
Jeff
 
So the '57's are the CEN type?

Did you solder 3 legs or 2 onto the board?
Also, as the MPSU57's have a different case, I used the clip on heat sinks as opposed to bolting them onto the PCB with the original heat sinks. I checked several times to be sure and there is no electrical connection to those studs but maybe there is a mystical connection that has been broken?!?!?!?
 
I just want to make sure I am not just churning water here.....

If in fact the deflection circuit was working correctly and producing the required voltages etc. I would hear the chatter. So since I do not hear that tell-tale chatter and also when I turn the brightness/contrast up, there is just a dot in the center of the screen, the problem does in fact lie in the X-Y deflection circuit and not the intensity or spot kill circuits????

Thanks - one way or the other, I will find the cause of this failure.
(I hope ;-) )
Jeff
 
Page 29 of this doc below is the diagram

http://www.arcade-museum.com/manual...146 Issue 2 Electrohome G05 Monochrome XY.pdf

The spot killer sensing line comes from the final stage of amplification at the x and y of the yoke

If either of x or y's signals are not present spot killer will activate

So all it would take is ANY 1 of the amplifying transistors to be dud and the spot killer would activate

I would check each stage with an oscilloscope till I found the dud one and go from there
 
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Yep, that's the doc that I have been using and using and using..........

I have to scope the PCB with the deflection transistors unplugged otherwise R620 and R720 get burning hot almost immediately. I compared the working monitor and when the deflection transistors are unplugged the spot kill is activated. I think that it should not be a problem, as the circuit I will be testing is before but I just want to make sure.

Off to the oscilloscope and thanks for the help, I don't feel so alone....... ;-)

Thanks
Jeff
 
OR . . . if one of the spot killer circuits was faulty, you would get spot killer when you are not meant to .
Just a thought ;)

That's another thought but like I said, I should still hear the chatter even thought the intensity circuit was "off" - right??
 
You can "overwhelm" the spot killer by turning the brightness up high. If you don't hear chatter and see a spot in the middle the screen, then you definitely don't have deflection.

Since you don't have any chatter/deflection I would start with the assumption that it's something common to both amplification circuits...Maybe a bad diode in the rectifier...Maybe a bad (shorted/open) capacitor in the power supply. Did you pull at least one leg when testing values (many components cannot be tested in circuit)? Did you verify that the high-wattage resistors aren't fried? Those resistors should be replaced with jumper wires, regardless (per Atari field guide). Also, make sure you test fuses out of circuit as well. Make sure all fuse holders are tight.

As others have stated--reflow all header solder joints. Heck, reflow everything while you're at it if you're really frustrated.
 
Veee need your answer here hmmm

As this was a complete rebuild, I had already replaced all transistors, (Hi, Med and Lo power), all diodes and all caps, (electrolytic and ceramic). Also replaced several resistors that were out of spec, namely:
-R621, 721
-R617, 717
-R618, 619, 718, 719.
I also tested R620 and R720, which read correct and even compared those readings to the working PCB and matched almost exactly. Also, they both get burning hot when the deflection transistors are connected to the board, so they are not "open".

The fact is that whatever is doing this is causing both channels to fail. I will have to bench this again and trace the signal as it propagates through the board. But as R620 and R720 get burning hot while the deflection transistors are plugged into the deflection PCB, I will have to do this while they are unplugged, which in itself will cause the spot kill to be activated! If I leave the deflection transistors plugged in, those resistors will fry........

Question: Can I troubleshoot the circuit, (bench the monitor) with the deflection transistors unplugged or with that cause my readings to be inaccurate??????

It is a possibility that a new component that I installed could be in fact defective, (won't be the first time) but why would one defective component effect both channels?

One last piece of the puzzle: When I swap a working deflection PCB into the monitor (G05-801) the monitor works perfect so the problem in on this board somewhere.........

Jeff
 
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