G07 B+ won't adjust

matthew180

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I recapped a G07, replaced the flyback, and the HOT. It worked fine for a while, then went out. I realized I did not do the B+ adjustment after recapping, but now it keeps blowing the smaller 1.25A fuse F901.

I lifted two wires (W416 and W420) that provide B+ to the rest of the monitor, basically isolating the main B+ regulator circuit, and now the fuse does not blow and I can measure the B+ output. B+ is pegged at 174VDC and is not adjustable via R909.

Does anyone have any suggestions as to what I should check?

Thanks,
Matthew
 
I recapped a G07, replaced the flyback, and the HOT. It worked fine for a while, then went out. I realized I did not do the B+ adjustment after recapping, but now it keeps blowing the smaller 1.25A fuse F901.

I lifted two wires (W416 and W420) that provide B+ to the rest of the monitor, basically isolating the main B+ regulator circuit, and now the fuse does not blow and I can measure the B+ output. B+ is pegged at 174VDC and is not adjustable via R909.

Does anyone have any suggestions as to what I should check?

Thanks,
Matthew

'generally' when you keep blowing the fuse, the hot or flyback is bad. Possibly a short somewhere else, but you said it was working for awhile? how long?

I think you need to measure your B+ when everything is connected for it to be relevant. Meaning , you need to fix your blowing fuse/bad flyback or hot problem before we start to attack the B+.
 
It worked for a few hours over a couple of sessions before failing.

So you don't think I can adjust B+ with the other part of the monitor disconnected?

What is the resistance supposed to be from the B+ test point to ground? I'm getting about 2 to 3 ohms, which seems really low to me.
 
It worked for a few hours over a couple of sessions before failing.

So you don't think I can adjust B+ with the other part of the monitor disconnected?

What is the resistance supposed to be from the B+ test point to ground? I'm getting about 2 to 3 ohms, which seems really low to me.

I'd have to get into a chassis and test. But I don't think that is relevant at this point.

I assume you have a charge in the B+ filter cap (careful if you haven't checked that yet). Take a screwdriver and short the positive and negative leads on the bottom of the filter cap.

Your flyback or hot took a dump unfortunately.

I'd pull the hot and measure it. (measure it to see if it is shorted to the frame or not first). If you have an extra flyback, drop it in and see what happens. (with new hot if necessary).

Just this week I have 2 flybacks that either lasted 10 seconds or less, or didn't work at all, and I wasn't thinking that they were the problem so I continued to blow fuses until they eventually took out 3 hots as well. Finally the 3rd flyback was good and all was well.
 
Bah, that would suck if it was the FB, I *just* replaced it (and the HOT) when I did the caps. I'll test the HOT. How does the HOT short to the frame? Is that due to incorrect install, or maybe the insulator failing?

Is there a guide somewhere that shows how a good HOT will read with the ohm meter or diode test? Also, can I check the FB, either in or out of circuit?

Any recommendations on a vendor for the FB and HOT?
 
Bah, that would suck if it was the FB, I *just* replaced it (and the HOT) when I did the caps. I'll test the HOT. How does the HOT short to the frame? Is that due to incorrect install, or maybe the insulator failing?

Is there a guide somewhere that shows how a good HOT will read with the ohm meter or diode test? Also, can I check the FB, either in or out of circuit?

Any recommendations on a vendor for the FB and HOT?

maybe to go youtube or look up buffett on here, maybe he has a link in his signature with all of his videos. I've learned a lot from him and continue to.

I buy my parts from security0001 and riptor on here. Never had a bad flyback from either one of these guys, and if I did, I'm confident they would stand behind it and replace it.

I think flyback testers exist, I do not have one.
 
Thanks for the links and vendor suggestions, I'll check them out. I have seen flybacks for sale with and without the focus and screen adjustments. Does it matter?
 
Thanks for the links and vendor suggestions, I'll check them out. I have seen flybacks for sale with and without the focus and screen adjustments. Does it matter?

yes i have all parts in stock if you need anything at my site. www.arcadepartsandrepair.com
all flybacks are specific to a chassis model and all will have focus and screen controls somewhere but not always located directly on the flyback transformer.
 
I have now replaced the VR, HOT, and FB. F901 does not blow now, but B+ is still pegged at 170V and will not adjust. This seems to be back where I was after my original re-cap, VR, HOT, and FB replacement, i.e. the monitor worked for a while but then failed completely.

I removed all the resistors in and around X901 and X902 and tested them out of circuit (they were all good). I also tested X901 and X902 out of circuit, and replaced them just to be sure, but still can't adjust B+.

I also pulled D905 and did an active test out of circuit, it was also good.

When I test the voltages around X902 I'm seeing 6.8V on both the emitter and collector. According to the schematic, 6.8V is normal on the emitter, but the collector should be around 71V. I thought for sure that an open R905 might cause that, but as I mentioned above, R905 tested find out of circuit.

Any suggestions on next steps?
 
It doesn't sound lime this is your problem , but if you remove x701 and plug the chassis in and get a pic, it's a vr problem.

After that cracks in the chassis? Start testing for continuity especially around the flyback.

Unfortunately I've had hv shutdown require many different solutions.

Changing previously new caps (the 47uf cap iirc)
Replacing Ic501
Replacing T501
Fixing bad traces
 
Thanks Tron Guy, I'll pull X701 tonight and see what happens (what does X701 do anyway?) After I posted last night I did some additional searching and found a lot of threads (mostly posted by you ;-) ) related to a high B+. I should have found the GO7 flowchart earlier... I feel like an idiot for posting before searching.

However, in a few cases the problem was a bad T501. Are these available? Is there a replacement part number for it?

Also, I really don't understand this circuit very well (or any monitor circuits). Does anyone have a version of the schematic marked up with boxes around the various sections, as well as voltage and signal paths?
 
Thanks Tron Guy, I'll pull X701 tonight and see what happens (what does X701 do anyway?) After I posted last night I did some additional searching and found a lot of threads (mostly posted by you ;-) ) related to a high B+. I should have found the GO7 flowchart earlier... I feel like an idiot for posting before searching.

However, in a few cases the problem was a bad T501. Are these available? Is there a replacement part number for it?

Also, I really don't understand this circuit very well (or any monitor circuits). Does anyone have a version of the schematic marked up with boxes around the various sections, as well as voltage and signal paths?

From what I hear T501 doesn't fail often (though it has twice for me). No replacements out there for T501. Parts chassis is your option on this.

To test it , pull T501, I look at the bottom with the 3 legs on the left. Then I use my meter on diode setting and check the reading on the bottom 2 of the 3 legs. there should be some reading. I think I got 60, or .60 when it is good. On my bad ones, I had zero reading.

Again I am going off of memory on this one, so it could be the top 2 of the 3 legs.

Maybe one of these guys who are truly experts like Chris25810 or Buffett have a good schematic. I always refer to a crappy looking one cut into pieces (on the internet).
 
Thanks Tron Guy, I'll pull X701 tonight and see what happens (what does X701 do anyway?) After I posted last night I did some additional searching and found a lot of threads (mostly posted by you ;-) ) related to a high B+. I should have found the GO7 flowchart earlier... I feel like an idiot for posting before searching.

However, in a few cases the problem was a bad T501. Are these available? Is there a replacement part number for it?

Also, I really don't understand this circuit very well (or any monitor circuits). Does anyone have a version of the schematic marked up with boxes around the various sections, as well as voltage and signal paths?

x701 is the xray protection circuit transistor. if you pull it out and your monitor works then check your B+ and i have found many times its something in the 900's on the board that is bad if you voltage regulator is testing good. there are a few others too if they all check out.
 
Pulled X701, no change, B+ is still +148V and won't adjust. X701 seemed to test fine on the bench, compared to another X701.

I got a spare GO7 PCB, so I pulled and tested T501. 55 ohms across one coil, about 0.5 ohms on the other. Both T501s that I have tested the same.

Pulled X501 and bench tested with a spare, seems good. Not shorted anyway. I can try the spare in the circuit for completeness though.

Tested continuity to ground on all caps that I replaced.

I have 160V on the HOT. So I'm out of options on the GO7 flowchart, down to the part that says "call Randy Fromm". Anyone have his number? ;-)
 
i have personally seen the IC501 go out after a cap kit but i think you have a crack somewhere which can sometimes be a real bitch to find and i would check continuity starting at flyback pins and working your way out and see what you have. i may have missed it but did this chassis ever work before the capping you did?
 
If you are sure that the flyback and horizontal output transistor are good. Next part I would replace is IC501. I'm seeing more of these fail.

Be sure to put a socket in for the IC.

If you need a second set of eyes to look at it PM me.

Ed
 
If you are sure that the flyback and horizontal output transistor are good. Next part I would replace is IC501. I'm seeing more of these fail.

Be sure to put a socket in for the IC.

If you need a second set of eyes to look at it PM me.

Ed

ed is that the car you had finished?? looks awesome.
 
i have personally seen the IC501 go out after a cap kit

I have a spare IC501 in the extra PCB I just picked up, but I don't know for sure if that it would be good. Are there any bench tests (or in-circuit measurements) to know if IC501 has failed? I'll order a few (assuming they are available), and pull it and put in a socket.

but i think you have a crack somewhere which can sometimes be a real bitch to find and i would check continuity starting at flyback pins and working your way out and see what you have.

Is there a list of FB to ground resistance measurements anywhere? The PCB is very clean and I have been constantly inspecting it.

i may have missed it but did this chassis ever work before the capping you did?

The monitor died from old age. At that point I did the caps, and replace the FB, HOT, and VR. It worked after that, but I forgot to check/adjust B+. After a few hours of operation it died again. That is where this thread picks up. Based on feedback I have replace the VR, HOT, and FB again to make sure they are good (the HOT had failed again for sure).

Now the monitor powers up (it was blowing a fuse before replacing the HOT for the second time), but B+ will not adjust and I don't leave it powered up for more than a few seconds to take measurements.

I have checked or replaced: VR, HOT, FB, X901, X902, X701, T501, C511, C523, *all* R9xx resistors in the voltage regulator section, and continuity to all electrolytic caps. I have pulled X501 and bench tested it, I will replace it just to be sure. I will also pull IC501 and replace it with the spare that I have (which is an unknown status).
 
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