Help with a A-One chassis

GoneMad

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Hi guys. I am now short one monitor and really need to get this A-one AP-0621 working. What I have to it so far was recapped and replaced to resistors and a few transistors on the neck board. There is neck glow and and color on the screen. I am not sure if it's the tube gone or what, I really hope not, this one is completely burn free and a replacement tube will be hard to find, and it has the skinny neck on it and I don't have anything else around I can test this on. Just wondering if anyone can help me on this with some key testpoints and what not. Here is a pic of what the screen outputs. Before it was green, it was an orange color. I do get a little response from the knobs on the flyback. I do have the schematics and the parts list for this chassis but still need some help or guidance. Thanks

IMG146.jpg
 
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One, looks like your green drive is up too high.

Two, have you actually hooked it up to a board yet?
 
Yes, I have hooked it up to 2 known working boards. Actually, the green drive adjustment is the ONLY color adjustment that does anything. If I turn the green drive down as far as it will go, and then adjust any of the blue or red, nothing makes any difference at all. The three transistors on the neck board have been replaced and I checked the ohms on the resistors and they seem to be in spec as well.

Also, when you look at the schematic, the tube number starts with A48JLL.... , and then says 20 inch. Would the A48 not mean 19 inch? Just checked, it is 19.
http://home.comcast.net/~mtpacifico...rean Telecom AP-0621 Parts and Schematics.pdf
 
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I found a section on arcade repair tips where they test the tube colors by shorting out the color pins to ground on the back of the neck board. The red and blue drive seem to be dead and green is the only color that will flash on the screen when it's pin is grounded. Would this pretty much indicate a hosed tube?

Well, i have to go to the facility and dump off a few old pc's. I will have a check and see if there are any 19" tv's I can get. Hopefully I can find one that will match.
 
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I found a section on arcade repair tips where they test the tube colors by shorting out the color pins to ground on the back of the neck board. The red and blue drive seem to be dead and green is the only color that will flash on the screen when it's pin is grounded. Would this pretty much indicate a hosed tube?

Well, i have to go to the facility and dump off a few old pc's. I will have a check and see if there are any 19" tv's I can get. Hopefully I can find one that will match.

You may have a bad tube, but if you do, it's not your only problem. Your green gun is working; you SHOULD be getting some kind of picture. Since you're not, you still have a chassis problem somewhere.

I don't know any "A-One" chassis, sorry.
 
You may have a bad tube, but if you do, it's not your only problem. Your green gun is working; you SHOULD be getting some kind of picture. Since you're not, you still have a chassis problem somewhere.

I don't know any "A-One" chassis, sorry.

Yea, that's what I was thinking as well. I re-flowed the whole chassis, replaced some of the obvious components on the neckboard, recapped etc. With this not being a very common chassis to trouble shoot, I'm thinking on replacing the video IC and see what that does. I don't want to keep throwing parts at it until I can get the tube replaced. I'm not that good at reading schematics or anything, so I have my work cut out. It sucks that the tube is hosed as it looks to be in very good condition.
 
Yea, that's what I was thinking as well. I re-flowed the whole chassis, replaced some of the obvious components on the neckboard, recapped etc. With this not being a very common chassis to trouble shoot, I'm thinking on replacing the video IC and see what that does. I don't want to keep throwing parts at it until I can get the tube replaced. I'm not that good at reading schematics or anything, so I have my work cut out. It sucks that the tube is hosed as it looks to be in very good condition.

I would hook the tube up to a rejuvenator before you dismiss it as bad. Your chassis could have deeper problems that the short trick doesn't bypass.
 
I would hook the tube up to a rejuvenator before you dismiss it as bad. Your chassis could have deeper problems that the short trick doesn't bypass.
I could see one color going bad, but red and blue? Does seem a little strange. This monitor does not look like it has had a whole lot of use. Is there a way to tell if each gun is getting power?
 
I could see one color going bad, but red and blue? Does seem a little strange. This monitor does not look like it has had a whole lot of use. Is there a way to tell if each gun is getting power?

Independent of chassis? Not that I know of, unfortunately. If I had a schematic I could make some guesses but it sounds like that's a bit of a tall order here.

I take it you don't have a rejuvenator? Where are you located? Wow, way out on the edge of Canada. I don't know of anyone anywhere near you :(
 
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Independent of chassis? Not that I know of, unfortunately. If I had a schematic I could make some guesses but it sounds like that's a bit of a tall order here.

I take it you don't have a rejuvenator? Where are you located? Wow, way out on the edge of Canada. I don't know of anyone anywhere near you :(
Yea, I'm pretty much on my own out here. No access to a rejuv.
Here's the schematic and parts list I have.
http://home.comcast.net/~mtpacifico...rean Telecom AP-0621 Parts and Schematics.pdf

BTW, thanks for everything so far.
 
Yea, I'm pretty much on my own out here. No access to a rejuv.
Here's the schematic and parts list I have.
http://home.comcast.net/~mtpacifico...rean Telecom AP-0621 Parts and Schematics.pdf

BTW, thanks for everything so far.

If you haven't already, swap Q18 with Q20. If the screen is now red instead of green, one or both of Q18/Q20 is bad, Q19 may also be bad; and also, your tube is (probably) good.

Compare (voltage) the bases of Q18/Q19/Q20 (if it's more convenient, follow the traces and test them at the connector; the schematic doesn't give a board marking for it). If Q18 is much different the others, your tube is (probably) good.

If not, compare R106/R107/R108 (lift a leg); their resistances should match (+/- whatever), likewise R96/R100/R104 (don't need to lift a leg on these). Replace any outliers, then try it again.

If the problem persists, set VR11/VR12/VR13 to match each other (I would meter them to be sure but it's not critical), pull Q18/Q19/Q20, power it up with the transistors not present (you won't see anything on screen; nothing is driving the guns, so this is normal), and compare (voltage) the holes where the emitters would be. If Q18's hole is significantly different from the others, chassis problem. If they're all the same, it's the tube. If you've verified R96/R100/R104, and the COLLECTOR holes are still different, then it DEFINITELY is the tube. FWIW, I'm not 100% sure it's safe to power up the chassis with the CDTs not present, but hey, what have you got to lose?

If you just wanna shotgun it, verify every resistor on the neckboard (except R105) by comparing it against its counterparts on the other channels, replace the caps (skip C49 if you want) and Q18/Q19/Q20, then check the drive signals from the HV board (bases of Q18/Q19/Q20). An outlier there indicates a problem on the HV board that'll throw the next test off. If everything checks out, turn VR12 all the way down (max resistance), VR11 and 13 all the way up (0ohm or close to 0). You should have a purple (red+blue) screen now. If you still have greenscreen, or nothing at all, it's the tube.

As an aside, instead of tossing it, I would troll eBay for cheap rejuvenators. Every now and then one turns up in an estate sale, or a storage locker, and gets sold off by someone that has no idea what it is other than it says "CRT Rejuvenator" on the front of it. I got a Heathkit from an estate seller for $25.
 
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If you haven't already, swap Q18 with Q20. If the screen is now red instead of green, one or both of Q18/Q20 is bad, Q19 may also be bad; and also, your tube is (probably) good.

Compare (voltage) the bases of Q18/Q19/Q20 (if it's more convenient, follow the traces and test them at the connector; the schematic doesn't give a board marking for it). If Q18 is much different the others, your tube is (probably) good.

If not, compare R106/R107/R108 (lift a leg); their resistances should match (+/- whatever), likewise R96/R100/R104 (don't need to lift a leg on these). Replace any outliers, then try it again.

If the problem persists, set VR11/VR12/VR13 to match each other (I would meter them to be sure but it's not critical), pull Q18/Q19/Q20, power it up with the transistors not present (you won't see anything on screen; nothing is driving the guns, so this is normal), and compare (voltage) the holes where the emitters would be. If Q18's hole is significantly different from the others, chassis problem. If they're all the same, it's the tube. If you've verified R96/R100/R104, and the COLLECTOR holes are still different, then it DEFINITELY is the tube. FWIW, I'm not 100% sure it's safe to power up the chassis with the CDTs not present, but hey, what have you got to lose?

If you just wanna shotgun it, verify every resistor on the neckboard (except R105) by comparing it against its counterparts on the other channels, replace the caps (skip C49 if you want) and Q18/Q19/Q20, then check the drive signals from the HV board (bases of Q18/Q19/Q20). An outlier there indicates a problem on the HV board that'll throw the next test off. If everything checks out, turn VR12 all the way down (max resistance), VR11 and 13 all the way up (0ohm or close to 0). You should have a purple (red+blue) screen now. If you still have greenscreen, or nothing at all, it's the tube.

As an aside, instead of tossing it, I would troll eBay for cheap rejuvenators. Every now and then one turns up in an estate sale, or a storage locker, and gets sold off by someone that has no idea what it is other than it says "CRT Rejuvenator" on the front of it. I got a Heathkit from an estate seller for $25.
OK, so far on your list. Q18,19 and 20 are all new, but I checked voltage on the base anyway. All are right around 13.5-13.6 range. Good there.
Next, I lifted a leg on R106, 107, and 108. All in in spec around the 5.6k ohm range. Good there.
R96, 100, and 104 are all bang on the 2.2kohm. Good there.

I never started on the next part, it's getting late and I had a late night last night. Ready to turn in for the evening. Thanks for everything so far
 
Ok, I finally found a replacement tube for t his beast. An exact drop in. Anyway, after the swap, I'm not much further ahead. I do get some response from the adjustment knobs, but it makes no difference to the screen with or without the video hooked up or not. I don't get that green screen anymore, this is more like a brownish, yellowish. This pretty much eliminates the tube now, just to find the culprit(s).
IMG254.jpg
 
I have been trying to do what I can to trouble shoot this chassis. I get adjustment with all the control knobs. I get change from the screen and focus controls on the flyback. What I don't get any feedback from is the color knobs. I only get change when I adjust the Green drive. None of the other Drive knobs or Gains work. I have replace the three transistors on the neck board and have checked all the resistors. Is there any possibility that the socket on the neck board could be bad?
 
Is there any possibility that the socket on the neck board could be bad?

It's possible... any damage would be plainly visible on the contacts themselves I think. Is it the type of socket connector that comes apart?

Did you check the pots themselves? The red and blue pots may just be bad. Check VR14 & 15 as well.

I think your original tube is a tad weak in the red and blue, but it may not be enough to make the tube bad. Your new tube is also slightly weak in the blue, but again, not enough to throw it out.

Inspect the traces on the neckboard, correct any shorts or broken traces. From there.. I don't have a whole lot of time to study the circuit, so I don't presently know what they should be, but I think you may have a problem with the common voltages/signals going into the neckboard. One hits R106/107/108, one hits R95/98/102, and one hits VR11/12/13. That last one might be the most interesting.
 
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It's possible... any damage would be plainly visible on the contacts themselves I think. Is it the type of socket connector that comes apart?

Did you check the pots themselves? The red and blue pots may just be bad. Check VR14 & 15 as well.

I think your original tube is a tad weak in the red and blue, but it may not be enough to make the tube bad. Your new tube is also slightly weak in the blue, but again, not enough to throw it out.

Inspect the traces on the neckboard, correct any shorts or broken traces. From there.. I don't have a whole lot of time to study the circuit, so I don't presently know what they should be, but I think you may have a problem with the common voltages/signals going into the neckboard. One hits R106/107/108, one hits R95/98/102, and one hits VR11/12/13. That last one might be the most interesting.

OK. I have pulled R106/107/108, R95/98/102, and also VR11/12/13, all out of circuit and tested. ALL are good. Where would one check the B+ on this thing? Would there be a test point on R02, with VR01 being the adjustment?
Not good to mix a couple beer and solder. I fumbled the iron in my right hand and caught it with my left between the index and middle finger by the tip of the iron. OUCH, fuck that stings. Being a plumber at one time, I'm used to it. Wondering if this could be a B+ issue or a issue from the video IC at U01?
 
OK. I have pulled R106/107/108, R95/98/102, and also VR11/12/13, all out of circuit and tested. ALL are good. Where would one check the B+ on this thing? Would there be a test point on R02, with VR01 being the adjustment?
Not good to mix a couple beer and solder. I fumbled the iron in my right hand and caught it with my left between the index and middle finger by the tip of the iron. OUCH, fuck that stings. Being a plumber at one time, I'm used to it. Wondering if this could be a B+ issue or a issue from the video IC at U01?

Er, what I meant is, those three sets of three have a common signal or voltage coming in from the neckboard, and you may have a problem there. Come to think of it, you may not be getting any color signals to the neckboard either.

At this stage I'd say your neckboard is good and you need to start looking hard at the HV board.
 
Er, what I meant is, those three sets of three have a common signal or voltage coming in from the neckboard, and you may have a problem there. Come to think of it, you may not be getting any color signals to the neckboard either.

At this stage I'd say your neckboard is good and you need to start looking hard at the HV board.

OK, thanks. To start I just pulled the HV transistor D1398 to check it. If this guy is doing it correctly, this could definitely be the culprit, or one of, if the pinout should be the same as he has it labelled in the video, and I am getting current between E and C, in one direction but not the other, and also B to E passes a small current with the leads swapped in both directions. Is this confusing? Here's the video I was going by. I do have a spare but it's a D1399.

http://www.youtube.com/watch?v=8VK_4gZU__I
 
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OK, I pulled this back off the shelf to give it a whirl after creating a jamma test bench and something for monitors. I hooked up the monitor and plugged in a 138 in 1 and hit the switch.
PICTURE!!! But not the greatest. But progress. I can't remember what I last did and probably didn't test it after. I still have a fair mess to work through to get this right. I think I am completely missing blue. Here are some of the controls that are working and not working.

On the neckboard..
R drive- yes
G drive- yes

B bias- no

On the chassis
Brightness -No
and there is no change during adjustment on the Red, Blue, and Green Gain of the chassis.

IMG286.jpg

IMG285.jpg
 
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