Question about tgsl

[waleed]

Waltr, what is just happening, I bought a new IC's (U107,U106,U105,U104),I placed them then I turned the device on (without coil) the heating problem is back again (100ohm resistor got so hot) and when I attach the coil and check the negative voltage it was like -1.2v and I also noticed the TR8 is getting so hot (even if I remove the coil but it stil getting hot).

First I just removed the solder from U107 pin8 (I removed the 12v from the IC),well the 100ohm resistor didn't get hot, but the negative voltage still -1.2v and TR8 still getting hot, I removed D6 to disconnect the negative voltage from all ICs,and I removed the coil but TR8 still getting hot, what would cause this?, all the day working on the device

[waltr]

Sounds like maybe TR8 failed.
With scope check signals on base of TR7 & TR8. These switch +8 & gnd to produce -6V.

Did you install sockets when the op-amps where off the PCB?

Check outputs of (with DVM & scope):
U104 & U105- should be near zero.
U107a- should be zero or negative.

[waleed]

Sounds like maybe TR8 failed.
With scope check signals on base of TR7 & TR8. These switch +8 & gnd to produce -6V.

Did you install sockets when the op-amps where off the PCB?

Check outputs of (with DVM & scope):
U104 & U105- should be near zero.
U107a- should be zero or negative.

Oki waltr, I took the part that getting hot of the board and tested it in the uni so it was normal no heating at all, do you think I have a short in the board or maybe there is a component is damaged or something?

https://i.ibb.co/qCf3rkc/20200302-105702.jpg
https://i.ibb.co/DLxHyDn/20200302-102042.jpg

[waltr]

Oki waltr, I took the part that getting hot of the board and tested it in the uni so it was normal no heating at all, do you think I have a short in the board or maybe there is a component is damaged or something?

https://i.ibb.co/qCf3rkc/20200302-105702.jpg
https://i.ibb.co/DLxHyDn/20200302-102042.jpg

Now Drive the base of those transistors with a 0-8V 7kHz square wave through the resistors.
Does it get hot?

[waleed]

Now Drive the base of those transistors with a 0-8V 7kHz square wave through the resistors.
Does it get hot?

Waltr I think no need to do that because I already removed U100 from the board also removed R11 and C4 and the resistors still getting hot

[waltr]

Waltr I think no need to do that because I already removed U100 from the board also removed R11 and C4 and the resistors still getting hot

I'm confused...which Resistors are getting hot??

When you wired the two transistors, R11 keeps TR7 OFF and R12 keeps TR8 OFF.

Why remove U100??
To Troubleshoot you need to step through the circuit from the beginning (TX Oscillator) and check each stage.

[waleed]

I'm confused...which Resistors are getting hot??

When you wired the two transistors, R11 keeps TR7 OFF and R12 keeps TR8 OFF.

Why remove U100??
To Troubleshoot you need to step through the circuit from the beginning (TX Oscillator) and check each stage.

When I tested them at uni I placed them back to the board, the coil wasn't connected so I turned the device on so they got hot again,then I removed U100 try again but still getting hot so I removed R8 and C4 but still the same,(U104,105,106,107 Still not connected).

[waleed]

Waltr I checked the oscillator (connected only TX), the waveform was so big so I reduced the time division to millisecond (before it was in micro second when the device was working),I think the frequency of TX got increased and it not stable idk why,
One question; to run the oscillator what I need to be connected on the board?

[waltr]

The oscillator is simply TR1, R1, R2, R3, C1, C2 and a 6.5mH inductor (TX coil)
I did prototype this oscillator on perf board to play with while waiting for the PCB's to come from SilverDog.

The oscillator running into U100 is required for the charge pump to create the -6V.

You can put a short across the RX pre-amp inputs (J2) to test the other circuits with no-signal.
This eliminates any AC Mains or other EMI that the RX coil will pick up.
Then the differentiator op-amps should have zero V dc outputs.

[waleed]

Waltr I solved the problem that causing R100 getting so hot (C26 was damaged so I changed it), but I still didn't find the problem that causing TR8 and TR11 getting hot, today I bought a new TR8 and TR11 and even U100 and some resistors that close to them, I placed them on the board then I connected the coil turned the device but there is no negative voltage and TR8 and TR11 got hot again ,even if I remove the coil but they still getting hot. What do you think that would cause this problem

[waleed]

I checked TX frequency it wasn't normal,it was too big, maybe a cap is damaged??

[waltr]

I checked TX frequency it wasn't normal,it was too big, maybe a cap is damaged??

Too Big as in Frequency is Too high? or as in Peak-peak amplitude too large?

For either, yes, a cap in the TX oscillator may be bad. It is not hard to damage the connection leads on many caps so a good possibility.

The charge pump trouble shooting STARTS with the TX oscillator. If this is not working properly then who knows what the charge pump will do.

As I mentioned before, I built the oscillator circuit on perf board to play with. I also wound a 10cm diameter 6.5mH coil to use for testing.
This smaller coil is easier to handle and good for just running the TX oscillator for testing.

[waleed]

Waltr, today I tested TX frequency at uni, well there something wrong, see the img below, it look like a pure sinusoidal, and even at pin6 of U100 the waveform wasn't as normal, what do you think is causing this?, TR1 maybe? But I'm sure it is working good i tested it, what do you think?, and TR8,TR11 still getting hot.

https://i.ibb.co/qNwhsTK/20200305-122005.jpg
https://i.ibb.co/GQz90dr/20200305-122038.jpg

[waltr]

I responded two days ago but don't see my post now!!!

The scope pics show a 14kHz signal at both the TX and U100 out.
Odd the U100 is not dividing, pin 6 should have divided the Oscillator frequency by 16.

The TX waveform looks good too good as you said. The waveform out of U100 looks correct amplitude and square.

[waleed]

I responded two days ago but don't see my post now!!!

The scope pics show a 14kHz signal at both the TX and U100 out.
Odd the U100 is not dividing, pin 6 should have divided the Oscillator frequency by 16.

The TX waveform looks good too good as you said. The waveform out of U100 looks correct amplitude and square.

But why U100 out didn't divide the oscillator frequency?, and TX shouldn't look as good as I have right?, it should have noise at top of the signal as in the img below

https://i.ibb.co/Z61fFdR/paintastic20200306-171233.png