Oh so close, but now what (new problem)

[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 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.