Good Deal? K7400 Issues

zenomorp

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Ok. I was cruising CL last night and found a listing for a 25" tube. I called the guy and he said it was out of a 25th Anniversary Ms Pac/Galaga. I asked about screen burn and he said it hardly had any. He also said it came with the chassis, but he admittedly said he didn't know much about these things.

So, I took a chance and told him I'd be by in the morning to pick it up. The price for the tube and chassis was $60. When I got there, I was saddened that the tube actually had quite a bit of burn...


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...but the chassis turned out to be a K7400 in GREAT looking shape. It looks as if it was NOS right out of the box....


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...but that's where the good news ends. Turns out it's blowing HOTs. He said it was just "ticking" and he changed the HOT and it would still keep "ticking." He also said he changed some of the caps and not others. I verified that the HOT does is fact check shorted in circuit. I haven't really done any other troubleshooting. Any quick advice? I have some new HOTs on the way already, but I also need to know where I can get a FULL 7400 cap kit besides Bob Roberts. Nothing against him, I just don't like going through the Money Order hassle. I can go that route if need be, but if there is anywhere else, that would be better for me.


Thanks guys.
 
hell no throw it back.

I recently picked up a burn free but "working" k71xx for $50. now i use the term working loosely as it definitely needs a rebuild but it is burn free and working as i said. (no ticking no dead hot ect..)

Honestly the bond between collector and Bob Roberts should be a strong one :)


edit: Looks like you already bought it tho?
 
Make sure the pot in the power supply section wasn't broken loose from the glue and turned up. Too high and you'll lose HOT's...
 
Make sure the pot in the power supply section wasn't broken loose from the glue and turned up. Too high and you'll lose HOT's...

No. The B+ and the shutdown pots are both still securely glued. The chassis is in such good condition, it doesn't appear that it's even ever been used, even though it has. I felt the price of $60 was fair because I was going to use the tube as a test tube for other chassis' anyway, so the screen burn is not an issue and I should be able to get the chassis going fairly easily. I am about 99% sure the seller tried to test it without using an ISO, so we'll see once I get a new HOT in there how it works out. I've been poking and prodding, taking various readings of diodes and such and everything appears to be good in circuit. Only the HOT reads shorted.
 
Its a good deal just for the neck board, as it is the newer version with better heatsinks for the transistors instead of the flaky clip on ones.
 
Thanks guys. I started troubleshooting this today. First step in any troubleshooting is to verify the issue. The HOT was in fact shorted, but I installed the chassis on the tube and sure enough. Nothing. The new HOTs that I ordered came in today so I installed one of them in the chassis and reinstalled it on the tube. SUCCESS! Picture came up and I let it run for nearly an hour with no issues.

I am 99.9% sure what happened was someone at some point in the past did something to cause the HOT to short. They installed a new one but didn't cut off the legs sticking out the bottom of the chassis so when they reinstalled it, the legs shorted to the monitor frame and took out the HOT again.

In any case. It's now good to go and I got a working tube, yoke, and K7400 in remarkable condition. Cost me $60 and $10 for the new HOTs. Not a bad investment. The screen burn is a bummer because it's noticeable during game play. I'd say on a scale of 1-10, it's a 3. Not that bad, but you CAN still see it. As my plans are to use the tube as a test tube for K7400 and their compatible kin, that's ok. The chassis alone in the condition it's in was worth the $60. Here are some pics...


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the colors and contrast are great on that tube considering.....nice purchase.
 
Nice find! Wish I could find a deal like that, that's relatively close to where I live....I need a new tube for mine.
 
Honestly for $70 +/- you did well considering the chassis condition.

do you grab your HOTs off eBay or at a local place? I've been eyeball'n some of the asian HOTs and VRs that ebay has to offer because of their pricing. but don't know if i want to bite just yet.
 
Honestly for $70 +/- you did well considering the chassis condition.

do you grab your HOTs off eBay or at a local place? I've been eyeball'n some of the asian HOTs and VRs that ebay has to offer because of their pricing. but don't know if i want to bite just yet.

I get them locally. There's a mom and pop electronics store here that has everything a bright eyed electrician/technician/repair guy could ever want.
 
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I get them locally. There's a mom and pop electronics store here that has everything a bright eyes electrician/technician/repair guy could ever want.

but but i'm bushy tailed!....

all we have here is a damn Radioshack :(
 
Damn, I had one of those monitors that was in a MK4. Did capkit, flyback, replaced other parts suggested by others and just couldn't get it to stop ticking. Just replaced it with a slightly burned K7000.

Gave the complete monitor away as a backup with the MK4.

Oh and it was completely burn free.
 
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