Oh so close, but now what (new problem)

[TinCanAlley]

Originally Posted by zeno

Its OK to run it out. The base waveform will not look the
same though.
Newer sets are more complex & wont run. They have start, shutdown
& closed loops that require different techniques. Thats when
the real fun begins...........

73 Zeno

The waveform will be different, but it will be there and should be enough to make sure the horizontal board is working properly?

[zeno]

Originally Posted by TinCanAlley

The waveform will be different, but it will be there and should be enough to make sure the horizontal board is working properly?

The hoz drive will be OK up to the C of the hoz drive transistor.
IIRC the HOT base will look more like a shark tooth than square.
It will be there.

73 Zeno

[TinCanAlley]

Originally Posted by zeno

The hoz drive will be OK up to the C of the hoz drive transistor.
IIRC the HOT base will look more like a shark tooth than square.
It will be there.

73 Zeno

I thought I wasn't supposed to go near the HOT w/out a hi voltage probe? Also, whose idea was it to make a transistor with the shell being the collector? Wouldn't it have been easier to make it a three lead unit and then you wouldn't have to worry about isolating it so as not to short to ground? I looked over the thing carefully and found the case is being energized by a lead on the screw hole.

[old_tv_nut]

Originally Posted by TinCanAlley

I thought I wasn't supposed to go near the HOT w/out a hi voltage probe? Also, whose idea was it to make a transistor with the shell being the collector? Wouldn't it have been easier to make it a three lead unit and then you wouldn't have to worry about isolating it so as not to short to ground? I looked over the thing carefully and found the case is being energized by a lead on the screw hole.

The high voltage retrace pulse is developed at the collector of the HO transistor, so if the transistor is removed, it does not occur, and you will be able to read the base waveform with an ordinary 10x probe.

The transistor collector is the substrate of the die, which has to be soldered to the case to get good thermal conductivity to the heatsink. Hence, the case will be connected to the collector. There will be an insulating washer and some thermal-conducting (but electrically insulating) grease.

[TinCanAlley]

Originally Posted by old_tv_nut

The high voltage retrace pulse is developed at the collector of the HO transistor, so if the transistor is removed, it does not occur, and you will be able to read the base waveform with an ordinary 10x probe.

The transistor collector is the substrate of the die, which has to be soldered to the case to get good thermal conductivity to the heatsink. Hence, the case will be connected to the collector. There will be an insulating washer and some thermal-conducting (but electrically insulating) grease.

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?

[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.

[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 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 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

[TinCanAlley]

Originally Posted by 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

So the four replacement HOTs are safe. No need to sacrifice any of them. I'm still am glad I bought 4 of them. At $3 each and $4 shipping, it's well worth having some spares.