19" K7000 Blows HOTs

[ManiN]

Another note too is that the monitor had a slight wave in the picture like ripples in water. Real light, but enough to be annoying. One guy said to replace the VR as a fix. Does anyone else agree in that may have been an indication the VR was bad all along? I had replaced the filter cap and checked grounds with no resolution to the wave before it died. Never did replace the VR though. Is the voltage rectified on the board itself? Maybe there is an alternating power slipping into the board causing the wave and also weakened the VR then eventually killing it and the HOT leading to the short and turning R301 into a toaster and also threatening to be a damn fire hazard.

 

[ManiN]

Doing some digging I found a good reference thread: http://forums.arcade-museum.com/showthread.php?t=161726&highlight=testing+IC4 Where this guy actually found a k7000 that was operating without the IC4 and had similar issues in the hula wavy action like I used too. There is also comment about the action of him putting in another IC4 to replace the missing one and it ended up driving the R301 large white 220Ohm 15W resistor to go nuts like mine. That is crazy, but may show in some situations the monitor will run unregulated, but has side effects such as killing HOTs and wavy screens...

This is making me think the voltage regulator on mine was taking a dump and finally did.

 

[PrairieDillo]

I put in a Hanterex flyback into one I was working on and then couldn't get it working. After sending said chassis to Chad (monitor boss) he told me that the flyback is bad. I tried to relay the message to bob and then I got basically the same results.

I don't want to anger Bob and get on his blacklist so I sucked up the loss and ended up paying for 2 flybacks to fix my Monitor

 

[ManiN]

went through the checks and still, the only thing that doesn't seem right is the IC4. Probing it I found that checking pins 2 to 4 seem to be shorted. Also pin 1 to 3 is appears open, not sure if either of those situations is normal. Feedback? Never checked a voltage reg. before. Thanks.

 

[THE COUNT]

went through the checks and still, the only thing that doesn't seem right is the IC4. Probing it I found that checking pins 2 to 4 seem to be shorted. Also pin 1 to 3 is appears open, not sure if either of those situations is normal. Feedback? Never checked a voltage reg. before. Thanks.

Pins 2 & 4 should not have continuity. Neither should 1 and 3 IIRC. And yes a bad VR will cause a wavy picture. When a K7000 is in HV shutdown and you remove D10, if the VR is bad and you usually get a wavy picture if the VR is bad..

 

[ManiN]

Ok right on. I checked D10 and it's in place and functioning. Maybe the VR was failing but not in full high voltage shutdown but enough to overload and short the HOT then providing the short.

 

[ManiN]

Ok, so I finally ordered and installed a new HOT and Voltage Reg.

I installed the chassis and now I get nothing. Irritated, I pulled it and checked the HOT to see if it burned and it did not. That led me to believe it's not getting high voltage. I checked the B+ and it's an astonishing 174VDC! I think it's in high voltage shut down now. Just going by the manual, it says to check c36 and IC2. I don't have a way to check the capacitance on c36 in the event the capacitance change will allow a higher voltage and kick in the HV protection. IC2 they want to use an oscilloscope to check it, and I also don't have one... I really don't want to order again and pay yet again more shipping for a hand full of parts...

I found a similar 4 legged cap on a k4500 board that's PS.015J 1500VK0321 and a radial CP-C 0.1(M) 1500V 79-1 cap but I don't think either are right. I think C36 is supposed to be 6100pF and I think those are 15000pF and 100000pF. I'll keep looking in my parts. Any ideas?

 

[THE COUNT]

Unsolder one leg of D10 and try it. If you get a pic then it IS in HV shutdown. Then go from there.

 

[ManiN]

Ok, but what's the possible side affects of running too high a B+? I really don't want to risk blowing more HOTs etc. like fuses.

 

[modessitt]

If you were going to blow the HOT, you would have already. You most likely have solder/trace issues. it's very common on the K7000 and can cause high B+. If it works with D10 removed, that just means the problem is in the power section. if it doesn't, then it it is in a different section. You'll still need to fix it.

Or pay to have one of us fix it for you...

 

[ManiN]

Hmm yeah, that would make sense. I've read elsewhere the traces are horribly thin and weak on here. I've also seen it on this one. There are a few spots where the traces are missing small amounts around solder joints. though they aren't open. I'll poke around for damaged traces and cold joints. I think it's time I grab a capacitance capable meter. I'll use that to check C36.

Thanks for the repair offer, but I'd rather keeping poking at it. I enjoy the learning.

 

[modessitt]

If C36 was bad, a simple diode test from a meter will show it to be so (zero reading). And it would most likely blow your HOT and fuse, too. Also check C38 (although that would blow your fuse, too.)

I posted a pic in the K7000 sticky showing the most common trace failure areas....

 

[ManiN]

I'm thinking it would be out of value. Just like you ran into in your post on the sticky. The manual mentions this same situation in the troubleshooting tree. Just something to check. I saw your pic for common problem areas and am going to use that to start.

Thanks for the advice!

I could be wrong, but it seems these k7000s are pretty problematic compared to others.

 

[THE COUNT]

I could be wrong, but it seems these k7000s are pretty problematic compared to others.

They aren't bad at all really. They have their problems like any other, but in general are fairly easy to diagnose. Reflowing ALL the solder on the chassis and neckboard is a good place to start with them IMO. And they do tend to have issue with solder pads lifting, especially on older ones. I think we see alot of problems with them on here because there are so many of them out there in use.

 

[ManiN]

So if the pads lift, as long as they are still connected well, they should be fine right? I've seen a few lived on mine. Like I said, they seem to be connected well though.

 

[THE COUNT]

So if the pads lift, as long as they are still connected well, they should be fine right? I've seen a few lived on mine. Like I said, they seem to be connected well though.

If a pad lifts but doesn't break free from the trace, it is still making a connection. But IMO it wouldn't take much to break the pad from the trace. So when I'm working on one and a pad lifts, I use a clipped cap legs to reinforce the connection.

 

[ManiN]

Poking around I found D18 was loose. Literally flopping as the solder had cleanly broken from the traces. This explains the original issues the guy I had bought it from was dealing with related to the yoke flip. The VR was already bad I believe. When I checked D18 before, I probed it from the top and missed the faulty connection.

Calling this repaired at the moment.

 

[baritonomarc]

Just for reference: which brand are those "bad out of the box" k7000 flybacks?

 

[cadillacman]

Poking around I found D18 was loose. Literally flopping as the solder had cleanly broken from the traces. This explains the original issues the guy I had bought it from was dealing with related to the yoke flip. The VR was already bad I believe. When I checked D18 before, I probed it from the top and missed the faulty connection.

Calling this repaired at the moment.

SWEET!!! good find man.

ill try to keep an eye on this thread, this may be sticky worthy..

 

[ManiN]

Yeah, it's still going well. Ultimately, D18's solder was cleanly separated from the actual trace. Not sure how this happens, but it is a pain to spot because it looks fine at a glance, but when you touch it, it will lift away from the trace because it isn't actually bonded. Being the trace was black, I think it may be one of those electrical corrosive phenomenons where it started at one point and propagated throughout the trace on either side then sat there and arced out creating the black surface. All that said, it's like the solder just never really bonded to the trace in the first place.