K4900 Question: Dead, measuring 23ohms between a/c terminals

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K4900 Question: Dead, measuring 23ohms between a/c terminals

I have a dead K4900. I've recapped it, changed the HOT, replaced F501, replaced R601 (measuring 40ohms, s/b 3.3ohms). Reflowed the 130v rail, verified continuity between R503 and Pin 9 on the flyback. (I've been reading!)

No, before I plug this back in, I want to verify something. I'm seeing a consistent 23ohms resistance between the a/c input terminals. Is this normal, or do I have a short somewhere?

Thanks!
 
Answered my own question: Got home from work and pulled out the Moon Patrol, which has a working K4900. It measures 22.8ohms between the AC terminals.

Let's plug it in and see if it works.
 
Update to the Update: Plugged it in. Making progress. I now have power to the flyback, evidenced by the large spark and smoke shooting out of the top.

Obviously, the flyback is bad. Is there something I should be checking that may have caused the flyback to go, or is it likely an isolated problem?

I have another chassis I've relegated to "parts," so I can pull the flyback from that one I don't know if it's good, but it definitely doesn't look burned.

Before I swap flybacks, what should I be looking at? Don't want to burn up my only spare.

Thanks!
 
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Why would you want to replace a bad part with a 30 year old used part? I could see doing that if there weren't any replacements available. However there are and they are not that expensive.

As for a cause of it going bad. Old age probably.

Rebuild the one you have as a parts board and keep it as a spare.
 
Why would you want to replace a bad part with a 30 year old used part? I could see doing that if there weren't any replacements available. However there are and they are not that expensive.

As for a cause of it going bad. Old age probably.

Rebuild the one you have as a parts board and keep it as a spare.

I'm using the 30 year old part because it's the one I have on hand. If it works, great. If not, I'll buy a new one. It's the difference between getting it working tonight and a week from now.

The "parts" board has a quarter-size hole burned out of it at one of the jumpers, so I'm not really interested in trying to fix it.
 
https://www.arcadepartsandrepair.com/store/monitors/monitor-flybacks/msh1fap08-k4900-k5501-flyback/

here is the link to the flyback you pm'd me on. i do stock the k4900 flyback and 17 other flyback models...;)

Thanks. I'll probably order one from you just to keep a new one on hand, but I think I'm at the end of my technical ability on this chassis. Something is arcing under the board near the HOT, but I can't tell what. I'm tired of messing with it.

I really need to be able to sit down with someone who knows what they're doing to fill in the knowledge gaps. Getting help on the forum is great, but nothing replaces one-on-one guidance.
 
my 4900 was arcing under the chassis also , there was a jumper under there that had a bad joint , it looked like at one time a quarter got in there and created a short ( is a round quarter size burn in the metal base of the chassis right under the location of the jumper)
 
my 4900 was arcing under the chassis also , there was a jumper under there that had a bad joint , it looked like at one time a quarter got in there and created a short ( is a round quarter size burn in the metal base of the chassis right under the location of the jumper)

I looked, but couldn't really see any evidence of arcing or burning under the board. I packed it up and am shipping it to Buffett today. I'm interested to see what he says is wrong with it.
 
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