Oh so close, but now what (new problem)

[N2IXK]

All you will see at the collector terminal with the HOT removed will be a DC voltage, around 150V or so.

You should see a horizontal drive waveform at the base terminal, but without the B-E junction drawing current, the waveform probably won't look right.

[TinCanAlley]

Originally Posted by N2IXK

All you will see at the collector terminal with the HOT removed will be a DC voltage, around 150V or so.

You should see a horizontal drive waveform at the base terminal, but without the B-E junction drawing current, the waveform probably won't look right.

Okay. Just trying to figure out what kind of testing I can do while waiting for the new HOTs to arrive. I'm pretty sure I blew it up when I shorted the wave shaper transistor. I'd like to test the wave forms of that module to make sure it's working properly before I put the HOT in. Hopefully the waveforms of that module will be unaffected by the removal of the HOT.

[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

[TinCanAlley]

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.

[Username1]

Then its shorted all the way around....

[Username1]

You should yank the driver transistor and check it using the video as a guide. Be sure to put it back right when yer done....

[old_tv_nut]

Originally Posted by TinCanAlley

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?

There will be no waveform at the collector lead. Disconnecting the HOT will stop the horizontal sweep and high voltage pulses from being generated. They are the most likely source that drives the ringing since they are the largest currents and voltages in the set, but may not have the ringing themselves anyway - they may only be exciting the ringing in related circuits. With the HOT disconnected, you can look for the ringing elsewhere, but it may no longer exist.

Edit: have you tried experimenting with auxiliary grounding wires just to see if the on-screen pattern changes? If you see a change, it will help to identify hot spots for the ringing.

[TinCanAlley]

Originally Posted by Username1

You should yank the driver transistor and check it using the video as a guide. Be sure to put it back right when yer done....

I've pulled and checked all the transistors on the horizontal board and they test okay. It's just the HOT that's dead.

[TinCanAlley]

Originally Posted by old_tv_nut

There will be no waveform at the collector lead. Disconnecting the HOT will stop the horizontal sweep and high voltage pulses from being generated. They are the most likely source that drives the ringing since they are the largest currents and voltages in the set, but may not have the ringing themselves anyway - they may only be exciting the ringing in related circuits. With the HOT disconnected, you can look for the ringing elsewhere, but it may no longer exist.

Edit: have you tried experimenting with auxiliary grounding wires just to see if the on-screen pattern changes? If you see a change, it will help to identify hot spots for the ringing.

The ground wires were next on my list. I got the new scope and was trying to isolate the ringing. From there I was going to check all the grounds by using a jumper to a good ground source. If that didn't work, I was going to look at the caps and resistors.

If I can get the ringing waveform back with the HOT removed, I'll continue my troubleshooting while waiting for the new HOT.

[TinCanAlley]

Okay, the darn Postal Service can't even get a package here from FL without misrouting it to IL. Looks like my new HOTs won't be here until tomorrow or Thursday. In the meantime, I'm going to build me a dim bulb thingy. I have a ceramic ceiling socket, outlet and lamp cord. I will run the hot through the socket/filament and into the hot side of the outlet. The neutral goes directly to the neutral of the outlet. In the socket will be a 75w incandescent bulb.

Now from most of the replies I've seen about power usage for this chassis, the bulb should restrict the amperage to .62, is that correct? So there should be no risk of the unit drawing too much power and killing the new HOT, right? And what exactly happens if it tries? The bulb should be a full bright with the normal current draw of the chassis, so how do I know if it's trying to take too much? Is a 100w too much? I believe that would be a draw of .83 amps.

I'll post pics of it when I'm done.

[TinCanAlley]

Okay, the dim bulb tester is done. She's not the prettiest, but she'll get the job done. I was going to wire in a switch, but decided to put a inline rotary on the cord. That'll make it less cluttered.

[DaveWM]

that is a common bulb limiter by a lot of folks for checking major shorts in a set, but I think zeno was looking more for shorts of the HOtransistor

quoting here

After replacing since you prob dont have a variac you should use
a "rubber fuse" to protect it. You have many of them, a 75W
lamp. Remove the wire from pin 4 of the FBT. Hang in the lamp in
one end to pin 4 & the other end to the wire. If it lights dim
& you get a small dim pix things are OK for now. If it glows
bright you have problems.........

stop quote.

the prob with just using a dim bulb as you have it (at the primary of the power trans) is if there is a prob in the circuit around the HOT it may still blow even with the dim bulb. I could be wrong though, as I thought these chassis have loosely coupled power trans that should limit the current to some degree. Zeno needs to chime in to clear up.

[TinCanAlley]

Originally Posted by DaveWM

that is a common bulb limiter by a lot of folks for checking major shorts in a set, but I think zeno was looking more for shorts of the HOtransistor

quoting here

After replacing since you prob dont have a variac you should use
a "rubber fuse" to protect it. You have many of them, a 75W
lamp. Remove the wire from pin 4 of the FBT. Hang in the lamp in
one end to pin 4 & the other end to the wire. If it lights dim
& you get a small dim pix things are OK for now. If it glows
bright you have problems.........

stop quote.

the prob with just using a dim bulb as you have it (at the primary of the power trans) is if there is a prob in the circuit around the HOT it may still blow even with the dim bulb. I could be wrong though, as I thought these chassis have loosely coupled power trans that should limit the current to some degree. Zeno needs to chime in to clear up.

Well I can jumper the hot and neutral of the outlet and put the hot and neutral of the plug end in-line with pin 4 of T207. That way don't have to undo all whole DBT and rewire it.

[DaveWM]

Originally Posted by TinCanAlley

Well I can jumper the hot and neutral of the outlet and put the hot and neutral of the plug end in-line with pin 4 of T207. That way don't have to undo all whole DBT and rewire it.

there you go, and you still have the dim bulb tester for other stuff.

[zeno]

Just to clarify the bulb does 2 things
1) limit the current to HOT to protect it. If something
is drawing to much the bulb drops the voltage to the HOT.
If you do it with a shorted HOT or damper the bulb will have
all the 125 V across it & it lights normal but fuses wont blow.
2) trouble shooting aid. Some sets like GE used one of the
white caps instead of five. If it opened the HOT will blow in
milliseconds. Other things also could. you usually WILL NOT
find the bad cap with simple test equipt. The bulb trick allows
you to "unload" one thing from the FBT at a time till you
get a dim bulb with some HV.

73 Zeno