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

[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..."

[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.

[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.

[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.

[ivconic]

Maximum emitter-base voltage (Ueb): 7V

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

[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]

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?

[Brian Deese]

Here are some better screen shots,of three cycles,and one up close. I think you can see the vert/hor divisions in the pics.Yellow is input to amp and red is output. Notice the difference in the pos and neg output of the amp due to the lower VE than VC. No inverted channels this time,enjoy.

[Brian Deese]

Have you checked D12&D13 and D15&D16?

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

[Brian Deese]

Yeah what he said...
Looks like you have dynamic damping on the coil.
Is this a homemade implementation or a commercial one? (fixing or making?)
Remove the damping portions (upper/lower) temporarily (lift resistors or diodes). See if you get what you'd expect.
Make sure offset is correct (play with it, or center with no input signal).
Make sure zero V on one side of schematic is connected to the zero V on the other.
+/- voltage seems very low - do you have that schematic? I'd expect higher.
Maybe something elsewhere is loading down your supplies.

I dont know what dynamic damping is bklein
It is a whites af-108 and I am trying to repair it.
I have centered the offset.
I have played with the offset in the past,I have got more sens with it offset from zero,but I dont remember the value.As of now its set at zero though.
I do have the schematic,I will post it.It uses linear regs made of discreet components.

[Brian Deese]

That may be another problem.

It's impossible to determine the timebase and amplitude/division from your photo.

I was going to tell you that your scope shot really looked OK to me considering the high gain; slow recovery would be normal... but then I can't understand why your output would be FOLLOWING the input instead of inverting it and being a mirror image. So maybe I just better shut up instead.

I can clear that up for you,I inverted the red channel on the scope because it was easier for me to see.I didnt tell you the coil was connected to the inverting input on the amp so I didnt think it would matter.I better get some better pics while I have your guys attention,I really want to get some service out of this machine.The thing uses linear voltage regs made up of lm2904 as a comparator(I think) and discreet transistors.I have not posted the whole schematic because I was trying to keep it simple,the schematic is large and over complicated for me anyway, and I have to scratch my head when I look at it.

[bklein]

Yeah what he said...
Looks like you have dynamic damping on the coil.
Is this a homemade implementation or a commercial one? (fixing or making?)
Remove the damping portions (upper/lower) temporarily (lift resistors or diodes). See if you get what you'd expect.
Make sure offset is correct (play with it, or center with no input signal).
Make sure zero V on one side of schematic is connected to the zero V on the other.
+/- voltage seems very low - do you have that schematic? I'd expect higher.
Maybe something elsewhere is loading down your supplies.

[porkluvr]

Is it normal for the positive and negative supplies to be different levels,last night I measured vc at 3.48v and ve at 2.82v if I recall.The other machines I have use 5v+/- supplies.If you change the hor division on the scope to see 3 cycles you can see the difference in the output of the amp.

That may be another problem.

It's impossible to determine the timebase and amplitude/division from your photo.

I was going to tell you that your scope shot really looked OK to me considering the high gain; slow recovery would be normal... but then I can't understand why your output would be FOLLOWING the input instead of inverting it and being a mirror image. So maybe I just better shut up instead.

[ivconic]

Have you checked D12&D13 and D15&D16?

[Brian Deese]

Is it normal for the positive and negative supplies to be different levels,last night I measured vc at 3.48v and ve at 2.82v if I recall.The other machines I have use 5v+/- supplies.If you change the hor division on the scope to see 3 cycles you can see the difference in the output of the amp.