Need Guru to look at 5534 scope shot,something is wrong.

[ivconic]

No I have not,can I test them in circuit?

I guess you can. If not; than at least lift one side from pcb.
If i understand circuit correctly; those are there for overvoltage protection.
BUY92 is cool, warm or hot?
Have you checked it?

[ivconic]

Type Designator: BUY92
Material of transistor: Si
Polarity: pnp
Maximum collector power dissipation (Pc): 30W
Maximum collector-base voltage (Ucb): 150V
Maximum collector-emitter voltage (Uce): 60V
Maximum emitter-base voltage (Ueb): 7V
Maximum collector current (Ic max): 7.5A
Maximum junction temperature (Tj): 175°C
Transition frequency (ft): 60MHz
Collector capacitance (Cc), Pf: -
Forward current transfer ratio (hFE), min/max: 40/80

[ivconic]

Maximum emitter-base voltage (Ueb): 7V

1N5341 (6V2) + reverse 11DQ03 (app.0.55V) = approx.6.75V

[Davor]

It looks as a perfect AC coupled response to me.
Check your probe, and ensure you have a DC reading on your scope. With DC reading your yellow traces should get straighten up and you'll lose a zero crossing thing.

[Brian Deese]

I guess you can. If not; than at least lift one side from pcb.
If i understand circuit correctly; those are there for overvoltage protection.
BUY92 is cool, warm or hot?
Have you checked it?

Nothing ever gets warm on this board,It is a really low power machine.Those buy92's are tiny metal can,about a pencil eraser and they have heat sinks about 1/2" diameter on them. I dont think there is anything wrong with the tx,the waveform from the coil looks just like I expect it to.What do you see,that I dont? I am still a novice at electronics.

[Brian Deese]

It looks as a perfect AC coupled response to me.
Check your probe, and ensure you have a DC reading on your scope. With DC reading your yellow traces should get straighten up and you'll lose a zero crossing thing.

Both of the scope probes are DC coupled,if thats what you mean.I only use AC coupling if I want to see ripple on the trace.

[ivconic]

Nothing ever gets warm on this board,It is a really low power machine.Those buy92's are tiny metal can,about a pencil eraser and they have heat sinks about 1/2" diameter on them. I dont think there is anything wrong with the tx,the waveform from the coil looks just like I expect it to.What do you see,that I dont? I am still a novice at electronics.

I see nothing more than you do. But Carl's suggestion made me think that something is not "in range" there:

Carl:
"...Most likely the coil is very slightly underdamped, not enough to see it on the scope but enough to make the preamp flip. Slightly reduce the damping R by adding a resistor in parallel (perhaps 10k) and see if it goes away..."

[Davor]

Both of the scope probes are DC coupled,if thats what you mean.I only use AC coupling if I want to see ripple on the trace.

OK, but how do you obtain the yellow trace? There is obviously some voltage divider in action. What kind of voltage divider is there?

Whatever you have, you'll find some kind of AC coupling.

I already like that rig. It is mostly the way I'd make a bipolar pulsed PI myself - knowing what I learned so far. With inverting opamp in a frontend and proper transistors for drives.

[Brian Deese]

OK, but how do you obtain the yellow trace? There is obviously some voltage divider in action. What kind of voltage divider is there?

Whatever you have, you'll find some kind of AC coupling.

I already like that rig. It is mostly the way I'd make a bipolar pulsed PI myself - knowing what I learned so far. With inverting opamp in a frontend and proper transistors for drives.

The yellow trace is the input to the 5534,I have the scope probe hooked on one of the overvoltage protection diodes.You mean because the yellow trace is small in amplitude? The overvoltage diodes limit the peaks to .7 volts, thats standard issue frontend correct? The red trace is the output and there is a test pin to hook the scope tp8. I was going to offer you the schematic when I saw some of your posts' but It seems you have your design figured out.I cansend the full size schematic to you,or its posted in the schematics section also.

[Brian Deese]

I see nothing more than you do. But Carl's suggestion made me think that something is not "in range" there:

Carl:
"...Most likely the coil is very slightly underdamped, not enough to see it on the scope but enough to make the preamp flip. Slightly reduce the damping R by adding a resistor in parallel (perhaps 10k) and see if it goes away..."

I have to pull those damping resistors back out,I know it. And if you look at the above picture the yellow trace alone you can see a tiny peak cross zero.But the red trace doesnt seem to follow it in time is my complaint. I am having trouble swallowing it because the coils only measure 185uH and the tx pulse is only 50uS,its a low power machine,and it already has 330r damping resistors.I just dont see how its ringing. But something is not right obviously.

[ivconic]

I have to pull those damping resistors back out,I know it. And if you look at the above picture the yellow trace alone you can see a tiny peak cross zero.But the red trace doesnt seem to follow it in time is my complaint. I am having trouble swallowing it because the coils only measure 185uH and the tx pulse is only 50uS,its a low power machine,and it already has 330r damping resistors.I just dont see how its ringing. But something is not right obviously.

That's why i suspected diodes and base "biasing" voltage. It is "fast" PI machine yet with bipolar transistor and not with fet. It is much more difficult to control bipolar transistor in such conditions, so any possible variations at base voltage would cause also something like "ringing" and indirectly will affect rx too.
I had similar issues long time ago with such "bipolar" design.
You actually don't need to resolder diodes to examine them; just measure voltage across them. (that's why i gave you reference 6.75V to start with)

[Davor]

The yellow trace is the input to the 5534,I have the scope probe hooked on one of the overvoltage protection diodes.

Ah, so you actually measure the opamp feedback compensated input, and not the voltage on the coil. OK, that makes sense. Trouble with such measurement is that you actually look at the place where a voltage should be different from zero only in times the opamp is saturated, and such measurements will lead you nowhere. This is very different from non-inverting opamp stages where input follows the applied voltage. The inverting one fights back and tries hard to keep its input at zero. What you observe is just the way the opamp recovers after saturation, and it is perfectly OK the way you see it.

[Davor]

It is "fast" PI machine yet with bipolar transistor and not with fet.

IMHO sexy MOSFETs just make it worse. BJTs may need some more juice to drive, but they do not introduce much capacity to the deal, like MOSFETs do.

A reality check: business part of the PI signal is a beginning of the off time, and that calls for high R. MOSFETS bring low R to the table ... not very useful, and it comes with high C attached to it.
Lower R -> higher C.
Low R unimportant, high C problematic -> to hell with low R MOSFETs.

[ivconic]

"...BJTs may need some more juice to drive..."

That's the spirit!

[ivconic]

What i ment: no wonder White's did it that way.
They do know how to "milk" the juice...