Oh so close, but now what (new problem)

[TinCanAlley]

Okay, I was getting so close to finding the jail bar problem, but it wasn't meant to be. I went to turn the set back on to scope a couple more points and all I got as a very loud buzzing through the speaker (even with volume all the way down) and then the circuit breaker went. I reset and tried it again, but turned it off before the circuit breaker went again.

I looked over all the boards and connections and found nothing out of place. Nothing is shorting and all the transistors are seated. The only thing I did was earlier when I put in a new 695 transistor in the ABL circuit. It was working for quite some time after that swap, so unless it was a delayed reaction, it doesn't seem to be that. And just in case, I put the old one back and still have the same issue.

So anyone know what could make the 25EC58 buzz and die?

Thanks!

[DaveWM]

did you ever replace the large oval metal cap?

[TinCanAlley]

Originally Posted by DaveWM

did you ever replace the large oval metal cap?

You mean that oil filled capacitor next to the large transformer? The 3.5uf @440V?

[DaveWM]

yes that one.

[Username1]

shorted power diode, horiz output transistor, shorted filter cap in power supply.

[TinCanAlley]

Originally Posted by DaveWM

yes that one.

Nope, it's the original.

[TinCanAlley]

Originally Posted by Username1

shorted power diode, horiz output transistor, shorted filter cap in power supply.

So if it were your set, where would you look first?

[DaveWM]

ok the usual suspects will be that plus the items the other items mentioned.

does the 3.3uf cap get hot before the circuit breaker kicks off? if it does get hot its prob bad.

If not then I would try disconnecting the horz out transistor (remove it from the socket). if it still kicks on then you need to start checking things like filter caps and diodes in the power supply.

[TinCanAlley]

Originally Posted by DaveWM

ok the usual suspects will be that plus the items the other items mentioned.

does the 3.3uf cap get hot before the circuit breaker kicks off? if it does get hot its prob bad.

If not then I would try disconnecting the horz out transistor (remove it from the socket). if it still kicks on then you need to start checking things like filter caps and diodes in the power supply.

Okay, I ran it until the breaker went. The oval canister didn't change temp (at least not that my hand could tell). Also, the HOT didn't change temp, either.

[TinCanAlley]

Okay, I took out the HOT from its socket and the set had a very low volume buzz and the breaker never tripped.

So what does this mean? Is the HOT bad, or is there something in between that needs to be looked at?

[TinCanAlley]

Well no matter what connections I do with the diode checking mode, the darn thing tones and shows a 9. Those were for negative on B and positive on E or C, Positive on B and Negative on E or C and negative on E and Positive on C. So I guess this thing is toast. Can only find an NTE replacement. Are those up to the job? Also, should I assume this thing went belly up due to something else in the chain?

I'll probably order a few of them since it might an issue elsewhere and kill the first one I put in.

[TinCanAlley]

Well I looked up the Zenith part number and got an NTE238. In the Sams there are 4 other suppliers of the HOTs, so I decided to look them up. What I found only confused me more. It seems that each part number comes up with a different NTE HOT, each with slightly different specs. So now the question is, which is closer to the original?

Here are the numbers I got: NTE238, 163A, 164 and 165. Those correspond to: TI, Motorola, International Rectifier, Sylvania.

[Findm-Keepm]

What's your original Zenith part number?? - the transistor may only be marked with a suffix, but the prefix will be 121- . Zenith made some Horizontal Output Transistor replacements as kits, with the skinny clear tube of Monkey-Snot heat sink compound and mica insulator. I remember the 4-lead safety cap CCII sets had a subbed horizontal transistor that didn't come as a kit - most others came simply by their 121- number. I've got some used-but-good Horizontal Output Trannys, but a part number is what would help right now.

Cheers,

[TinCanAlley]

Originally Posted by Findm-Keepm

What's your original Zenith part number?? - the transistor may only be marked with a suffix, but the prefix will be 121- . Zenith made some Horizontal Output Transistor replacements as kits, with the skinny clear tube of Monkey-Snot heat sink compound and mica insulator. I remember the 4-lead safety cap CCII sets had a subbed horizontal transistor that didn't come as a kit - most others came simply by their 121- number. I've got some used-but-good Horizontal Output Trannys, but a part number is what would help right now.

Cheers,

What's installed is a 121-831 and is made by TI.

[TinCanAlley]

Originally Posted by Findm-Keepm

What's your original Zenith part number?? - the transistor may only be marked with a suffix, but the prefix will be 121- . Zenith made some Horizontal Output Transistor replacements as kits, with the skinny clear tube of Monkey-Snot heat sink compound and mica insulator. I remember the 4-lead safety cap CCII sets had a subbed horizontal transistor that didn't come as a kit - most others came simply by their 121- number. I've got some used-but-good Horizontal Output Trannys, but a part number is what would help right now.

Cheers,

How likely is it that it died on its own and plugging in a replacement is safe? If it's not that common, what should I look for before installing it and risk damaging it?