Oh so close, but now what (new problem) - Videokarma.org TV - Video

TinCanAlley · #1 09-18-2013, 02:31 PM

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 · #2 09-18-2013, 05:41 PM

did you ever replace the large oval metal cap?

TinCanAlley · #3 09-18-2013, 05:50 PM

Quote:

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 · #4 09-18-2013, 05:51 PM

yes that one.

TinCanAlley · #5 09-18-2013, 05:53 PM

Quote:

Originally Posted by DaveWM

yes that one.

Nope, it's the original.

DaveWM · #6 09-18-2013, 05:57 PM

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.

Username1 · #7 09-18-2013, 05:51 PM

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

TinCanAlley · #8 09-18-2013, 05:54 PM

Quote:

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?

Username1 · #9 09-21-2013, 05:11 PM

"" So let me make sure I get this correct. With the HOT removed I will be able to connect my 10x probe to the collector lead of the HOT socket?

Will the waveform I get be enough to see the ringing if it exists? ""

The horiz. output transistor, like the horiz. output tube, drives the next stage, the horizontal output transformer, high voltage transformer. The pulse at the base of the transistor turns it on and off quickly, making pulsating dc, the quick turning on and off, the transformer responds to as if it was AC, making the high voltage on the output side (secondary). The collapsing magnetic field on the "off" state of the HOT will also develop a high voltage spike on the primary, (thats the transistor's side) that spike can kill your scope, and most meters if you try to measure it. So normally, you don't try. With the transistor out, the part of the circuit making the bars is partly, mostly disabled, not developing the bars. Also since the transistor is not driving the transformer, only the B+ should be on the "C" leg of the transistor, no wave shape to speak of.... No high voltage either. Think of this part of the circuit like the coil, and points in your car, or electronic ignition if you want to think of it like that.

Removing that transistor, is done mostly to see if the signal, and voltages are correct at the base, if its a NPN and the base is too positive, it will overdrive the transistor, burn it out or the horiz. transformer.

You could just put a 1 amp fuse in line with the "C" or "E" of that transistor, less expensive than a transistor.....

Check your Horiz Transistor:

http://www.youtube.com/watch?v=REW2lF0sb74

TinCanAlley · #10 09-21-2013, 05:24 PM

Quote:

Originally Posted by Username1

"" So let me make sure I get this correct. With the HOT removed I will be able to connect my 10x probe to the collector lead of the HOT socket?

Will the waveform I get be enough to see the ringing if it exists? ""

The horiz. output transistor, like the horiz. output tube, drives the next stage, the horizontal output transformer, high voltage transformer. The pulse at the base of the transistor turns it on and off quickly, making pulsating dc, the quick turning on and off, the transformer responds to as if it was AC, making the high voltage on the output side (secondary). The collapsing magnetic field on the "off" state of the HOT will also develop a high voltage spike on the primary, (thats the transistor's side) that spike can kill your scope, and most meters if you try to measure it. So normally, you don't try. With the transistor out, the part of the circuit making the bars is partly, mostly disabled, not developing the bars. Also since the transistor is not driving the transformer, only the B+ should be on the "C" leg of the transistor, no wave shape to speak of.... No high voltage either. Think of this part of the circuit like the coil, and points in your car, or electronic ignition if you want to think of it like that.

Removing that transistor, is done mostly to see if the signal, and voltages are correct at the base, if its a NPN and the base is too positive, it will overdrive the transistor, burn it out or the horiz. transformer.

You could just put a 1 amp fuse in line with the "C" or "E" of that transistor, less expensive than a transistor.....

Check your Horiz Transistor:

http://www.youtube.com/watch?v=REW2lF0sb74

The transistor doesn't have the built-in damper diode. When I test it (like in the video), the diode function of my DMM beeps in any combination telling me there's continuity between all. The number are 009 and 002 on the display.