quick question before I start to recap a k7400

tron guy

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The monitor isn't power up (no neck glow) I see a 100uf 200v cap with the top blown off.
The fuse is good

before I go and do the cap job, I'm just curious if just that 1 cap being blown could cause this monitor to shutdown?

I was anticipating that I may have several issues, but the fuse being good and the flyback looking clean has me mildly optimistic on this one.

I can't remember where/how to test the b+ on this thing.
 
The chassis has OTHER faults - replacing caps will NOT fix it.

It certainly might be required that some caps need replacing but caps don't stop chassis from working.

that was my assumption as well

I thought since the fuse didn't blow I have a chance of less things being bad than I originally anticipated.
 
I would probably check some other things out with the old caps in there. Shouldn't hurt anything because if there is something else bad in there causing the caps to blow once you put the new ones in it may blow those too. Just how I would approach it. Make sure the right fuse is in there and always check it with a meter.
 
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I would probably check some other things out with the old caps in there. Shouldn't hurt anything because if there is something else bad in there causing the caps to blow once you put the new ones in it may blow those too. Just how I would approach it. Make sure the right fuse is in there and always check it with a meter.

well the fuse is good, I checked it.

1 cap is blown I have to check the position, but it's the only 100uf 200v cap on the board (IIRC)

yeah I suppose I ought to test the voltage regulator and hot, but what is the liklihood of those being bad and the fuse being good? (high?low?)

where do you test the b+?
 
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Thank you buffett. lol

Also Tron_guy can you tell me the number on the board where that blown cap is located? Looks like it might be C115 if that's the only 100uf 200v cap like you say and guess what? It's very close to B+ and the test point. I would def check that B+ as well as the diodes and the resistors in that area. The TP would be in the C-9 area marked on your board and there should be a fairly large diode with beads on the leads I would especially check. But check everything around there.
 
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Thank you buffett. lol

Also Tron_guy can you tell me the number on the board where that blown cap is located? Looks like it might be C115 if that's the only 100uf 200v cap like you say and guess what? It's very close to B+ and the test point. I would def check that B+ as well as the diodes and the resistors in that area. The TP would be in the C-9 area marked on your board and there should be a fairly large diode with beads on the leads I would especially check. But check everything around there.

yeah it's C115. now I'm caught up in rebuilding this peter chou power supply so the k7400 is for another night.

thanks
 
C'mon I can solder in 10 caps in the PS in .02424523045 seconds. lol just messin. Anyways 1 thing at a time. I don't know how much longer I'll be around when I get a job and I need one FAST. =(
 
C'mon I can solder in 10 caps in the PS in .02424523045 seconds. lol just messin. Anyways 1 thing at a time. I don't know how much longer I'll be around when I get a job and I need one FAST. =(

well I changed the 4 most likely caps to be bad according to ken's log. It's firing up every time now. It could be randomly working, I will ahve to wait and see, but it wasn't firing before and sitting at 3v on the +5 so I'm optimistic.

new fan and 4 caps. saved me $60 (fingers crossed)
 
Ya when you said it was fine after you fired it up and said it lost the voltage it pretty much meant ur caps weren't keeping the voltage like they should. They are like a battery in a way. Hope you replaced them with Panasonic or Nichicon caps so they last! =)
 
Ya when you said it was fine after you fired it up and said it lost the voltage it pretty much meant ur caps weren't keeping the voltage like they should. They are like a battery in a way. Hope you replaced them with Panasonic or Nichicon caps so they last! =)

this thread is getting a bit crossed with my other thread, but, I used good caps. And I've fired it up several times, so it looks like a successful power supply rebuild.
 
Was just waiting for you to get back if the diodes and etc were good on the chassis. Just trying to help..
 
Was just waiting for you to get back if the diodes and etc were good on the chassis. Just trying to help..

oh I appreciate it!

not gonna mess with the chassis tonight. Instead i got this power supply done, finished a tube swap and have a brand new screen with a rebuilt g07 chassis on it. almost too nice to use. not sure what is worthy. :)
 
ok back on topic with the k7400


Like I said that cap is blown up in the center of the chassis. I am looking over the chassis and I see what appears to be another blown up cap (I can see cap remnants pasted everywhere, lol), it was a 2.2uf cap. they replaced it with a 4.7 uf cap.

Again I haven't done anything to this yet to troubleshoot, and I just recapped the neck board is all, but could that 4.7uf in the place of what calls for a 2.2uf be the cause of other failures? Namely the other cap blowing up (C115) or whatever it was I mentioned in this thread a few weeks back.



I guess I'm holding out hope that the flyback is still good. Speaking of flybacks, would a flyback from a k7500 25" med res work in a k7400? They look the same, there is 1 slight difference in model # though.
 
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I pulled a k7400 chassis from a game with the exact same issue.. I installed a new cap, reflowed a lot of solder.. Especially around the trannies on the neck pcb.. And it works to this day! (8 months now)

I'd usually do more work to it, but it was a quick cheap favor for a local op.

Good luxk

Oh, and a k7500 flyback is the same as a k7400
 
The chassis has OTHER faults - replacing caps will NOT fix it.

It certainly might be required that some caps need replacing but caps don't stop chassis from working.

That is the biggest load of shit on this section of the forum. Caps may not be the ONLY problem, but I have seen - and fixed - hundreds of chassis where the only problem is bad caps. For example, the majority of dead 4900's seem to be fixed with just a cap kit - and sometimes some solder reflow.

Caps age and fail. It's a known fact. Plus there was a rash of bad caps manufactured several years ago and many of them probably ended up being installed on these chassis. Sometimes the failure is accelerated due to other issues, and sometimes the failure causes other issues, but there are plenty of times when the failure just puts the chassis in shutdown and it will stay that way until the bad cap(s) are replaced.

However, while pulling a chassis to replace an obviously bad cap, it is recommended that you check the major possible-fail components - HOT, VR, flyback, solder joints, fuses - while you have it out. And if you by chance replace ONE OR TWO caps and it's working again, you should have replaced all the caps. If one has failed due to age, heat or stress, the others may be close to failing too. No sense in pulling it out every month to replace a couple caps. Do them all...
 
The chassis has OTHER faults - replacing caps will NOT fix it.

It certainly might be required that some caps need replacing but caps don't stop chassis from working.

i have replaced one or two caps on k7000s and they powerd back up no problem, they cause HV shutdown sometimes.
 
well thanks for the feedback gentlemen, I'm encouraged with this chassis.
I will report back after I cap and test it.
 
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