k7000 25"-with video input pcb gets a trace fried?

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k7000 25"-with video input pcb gets a trace fried?

I have a buddy of mine dropping off a 25" k7000 monitor for me to take a look at.

He recapped it, and installed a new flyback.

Initially he powered it up with no signal input and the monitor appeared to have a screen and be working. After that he said he plugged in the video signal and there was a puff of smoke (or something to that effect), and it burnt up a trace on his arcadeSD pcb.

I don't think I've ever heard of this happening, but I thought I'd ask if anyone else has ever experienced this. I'll likely test it with my TPG before I do anything else.

oh yeah, apparently the main chassis fuse blew as well.

I'll report back when I know more. I just thought I'd start the thread in case anyone cared to comment.
 
Well I thought I'd check this one out today.

Like every other test I do on a monitor, I pull it up to the back of my wacko cab (very convenient to work out of).

Connect everything, boom, dead. Fuse on k7000 chassis is fine. It never saw any power.

F1 the MAIN fuse 3A 250 SB fuse was blown on my power brick.

tried it again, (because who doesn't like wasting fuses), blew it again.

I haven't dug into this chassis at all, but I'm curious what others have seen in a non-working k7000 chassis that can just cause the cabinets main fuse to blow immediately.
 
if it wasn't plugged into an isolation transformer, the diodes will be nuked. dead short on the diodes should theoretically cross the AC wiring to the monitor into each other, and that should blow the line fuse. which is different than a singular component within the monitor chassis being bad and blowing the monitor fuse.

it's never happened to me but I've heard of traces on game boards getting blown up in this condition as well. most horror stories involved the Midway games like MK3 or KI.
 
if it wasn't plugged into an isolation transformer, the diodes will be nuked. dead short on the diodes should theoretically cross the AC wiring to the monitor into each other, and that should blow the line fuse. which is different than a singular component within the monitor chassis being bad and blowing the monitor fuse.

it's never happened to me but I've heard of traces on game boards getting blown up in this condition as well. most horror stories involved the Midway games like MK3 or KI.

thanks
I figured it was the diodes and I'd check R103 while I'm at it.

I'll report back.
 
Many years ago I was working on a Sega Galaxy Force. The original monitor went out and the operator didn't want to repair it. Instead we used a 25" K7000 monitor. Was an interesting feat to get it mounted. Well long story short. Fired up the game. Blew out the monitor chassis and the game board. Fried every video input trace and many parts on the game board and multiple parts on the chassis. Of course no manual for the game. End result no isolation transformer was required for the original monitor. And this was before the switching mode power supplies on chassis. So from then on always made sure there was an isolation transformer.
 
I pulled and tested diodes 19,20,21,22

20 and 21 were bad. I replaced them all since i had them out 1n4007 per bob roberts.

Power it back up, blows my cabs main fuse again.
I just pulled r103, it tests at 2.5-2.6 so thats fine. My new replacement is like 3.2. I dont see any reason to replace r103.

I need to read up a little and decide what to do n ext.

Chassis fuse is still good, fyi


Edit: does this VR look correct? I work on these so infrequently, I can't remember.
 

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What happened was, he was operating it without an isolation filter in the cabinet. once he plugged the video in, the video ground connected to the neutral from the a/c and fried the line on the monitor chassis, it may have smoked up his game board too. I did the exact same thing in a Killer Instinct one time.

Now that the monitor has been fried, you're trying to get the monitor chassis back up and running but don't let him put it back into whatever cabinet he was putting it in, because it will happen exactly the same next time.

Check the chassis fuse to make sure it's 2amp, or 2.5amp (I think they're different on some of the chassis) also make sure it's 125v (at least).
 
Ive seen this happen when someone bent the large resistor on the side so that it was touching the metal plate.


I didn't picture what you meant well enough. I assumed you meant r103, but after reading this again, I now think you were referring to the resistor where you test b+. I'll go check that now.

What happened was, he was operating it without an isolation filter in the cabinet. once he plugged the video in, the video ground connected to the neutral from the a/c and fried the line on the monitor chassis, it may have smoked up his game board too. I did the exact same thing in a Killer Instinct one time.

Now that the monitor has been fried, you're trying to get the monitor chassis back up and running but don't let him put it back into whatever cabinet he was putting it in, because it will happen exactly the same next time.

Check the chassis fuse to make sure it's 2amp, or 2.5amp (I think they're different on some of the chassis) also make sure it's 125v (at least).
It's 2amp I believe (250v)
 
I'll play captain obvious I guess. :)

the K7000s I've seen had the fuse silked as either 1.5 or 2A. I use 2A in the replacements. the point Lyons is making is if the monitor fuse was too high, it would survive, and then it passes down to the cabinet line fuse.

R301 is the large resistor on the side; never really thought about the tabs touching the frame before, so I'll look for this from now on.

looking over a chunk of the AC circuit in the schematic it looks like the following are probably important: R103, R101 (these take a lot of abuse and should probably be replaced with cap kits; particularly verify solder joints), IC4, IC2, R301 (check what Lyons said above), R89, C57.

I don't think the voltage regulator would totally short bad enough to do this... normally they just make the B+ peg at about 170V both ways.

you got one of those complicated ones Buffett talks about sometimes.
 
I had previously performed a good reflow throughout the chassis. I went through and doubled my effort. All the solder points are good though.

I didn't find any cracks, had continuity all around R103 and that area.

I guess I am trying to figure out why :

First it blew my cabinet main power fuse

then, when I find the 2 bad diodes and replace them , it still acts the same exact way. Blowing the main power fuse in my cabinet.

I pulled one of the diodes I had just replaced to test and it was still good. I didn't pull all 4 again, but I suppose I could.


Oh, and the resistor on the side of the chassis is in perfect order, it's not bent or tweaked, and it is certainly not touching the chassis in any incorrect way.
 
The poly caps short often on these chassis', especially the c36. Check all of them near the fly. When the c36 shorts, it will sometimes make you think the hot is shorted.
 
The poly caps short often on these chassis', especially the c36. Check all of them near the fly. When the c36 shorts, it will sometimes make you think the hot is shorted.

I hear ya, and I thought about pulling those.

Currently the state of this chassis is the same as it was when I got it.

Powering up the chassis, blows the main power fuse in my cab. Even after replacing the 2 bad diodes.

It's not the chassis fuse that is getting blown.
 
Have you tried it without the monitor plugged in, to make sure the cabinet isn't damaged and blowing the fuse on it's own now?

I am using the monitor with my wacko cabinet. My wacko runs perfectly (after I replace the fuse each time).


I'm not connecting the wacko pcb to the 25" monitor, just my TPG. And yes the power is coming from the wacko cab (hence the main fuse getting blown).
 
Are the 2 a/c wires shorted at the power connector on the chassis? If that's the case, I would stop trying to power it up. Check those poly caps, you can check them in the chassis. If you think ones shorted, pull it and check continuity on the power connector again.
 
Just a quick thought... but can't you do the same "resistor / Jumper" pull on the K7000 that you can on the 7400/7500 series and just power on the power supply? AKA: light bulb test.

Doing that will tell you if you have a power problem or if it is in another section of the chassis....
That way your not looking at the entire chassis for a issue just a part of it.
 
Are the 2 a/c wires shorted at the power connector on the chassis? If that's the case, I would stop trying to power it up. Check those poly caps, you can check them in the chassis. If you think ones shorted, pull it and check continuity on the power connector again.

None of the caps are shorted (while testing in circuit). There is no molex on this particular chassis. I've been running it to my molex connector via custom connector I use whenever I get chassis of different molex type or no molex at all.

The 2 points on the bottom of the chassis where the AC wires enter are shorted to each other, but that doesn't seem odd to me. If I pull the fuse, there is no longer continuity. I checked it on another k7000 I have here, same thing.

Just a quick thought... but can't you do the same "resistor / Jumper" pull on the K7000 that you can on the 7400/7500 series and just power on the power supply? AKA: light bulb test.

Doing that will tell you if you have a power problem or if it is in another section of the chassis....
That way your not looking at the entire chassis for a issue just a part of it.

I'm not familiar with this process.
 
none of the poly caps test bad (again in circuit)

I tested the diode that shares the pad with C37 (saw buffet mention this in an older thread), it was good.

I pulled most of the resistors in line with the a/c power-all tested good.

I thought I was getting a short on the B+ filter cap. (random beeps when I tested it over and over). I pulled it-548 UF reading, so no problem there. (and it wasn't shorted out of circuit either)
 
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