Question about tgsl

[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

[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 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?

[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).

[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]

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]

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]

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]

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]

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

[waleed]

First I used 10k but the sound wasn't so loud when I turn the pot to max, so I put a 100k and it worked fine,and I connected it to the ground not to tho he -5v, I didn't know that would make the 100ohm heating, so what you suggest for volume control other way

[waltr]

Waltr, I was adding a pot from TR2 collector to the ground for volume control (I saw you posted that somewhere in the forum),and when I removed it the heating problem is gone and the current becomes like 40mA with coil connected, are you sure you have a volume control connected like this way?, and tomorrow I'll buy a new ICs which I have removed and will see what would happen.

Read my last post, ,do you know other way to add volume control?, which method you use

Ahh..I posted while you were posting last one.

I have never put a volume control on the TGSL. I take the TGSL audio out to a BlueTooth module - to BT headphones which have volume control. Works great without the cord.

I did make some suggestions on what to try but currently do not remember what they were.
A link or picture will help my memory.

Ok, I just found the LTspice model I did for the Volume control.
This shows that bringing the base of TR2 to ground or lower, turns Off the audio and the current through the 100 Ohm resistor drops to Zero.
No R to ground has audio out at 1Vpeak into 8 Ohm, max volume.
3k Ohm to ground drop Vpeak to about 0.4V which should reduce volume.
I would try a 20k pot.

What value Pot did you connect?
Did you Ohm the Pot connection to ensure it was connected properly and you got the correct resistance range.
Connected to Ground and Not +5?

I do have a second TGSL EDU PCB that I should build just to do testing and experimenting on.
I do not want to experiment with the full detector I use since there is a good chance to break it.

[waleed]

That 100 Ohm resistor is power to the Audio transistors. This audio circuit is NOT designed to be on 100% of the time so makes sense the 100 Ohm gets hot if it is constantly beeping.
Maybe the transistor is now bad. Try removing it and re-check- better to trace the signal back as follows.
Or it could be the LM358 (U107) that is bad holding the audio transistor on.
Or could be the comparators (U106) turning on U107 and then turning on the audio.
Or could be a short or other problem on the traces from U104, U105 outputs into the comparators inputs. Ensure Pins 3 & 5 are lower than the references pins 2 & 6.


Current draw with the Audio Beeping is about 150mA. With no sound the current draw should be closer to 50-60mA.

Read my last post, ,do you know other way to add volume control?, which method you use

[waltr]

That 100 Ohm resistor is power to the Audio transistors. This audio circuit is NOT designed to be on 100% of the time so makes sense the 100 Ohm gets hot if it is constantly beeping.
Maybe the transistor is now bad. Try removing it and re-check- better to trace the signal back as follows.
Or it could be the LM358 (U107) that is bad holding the audio transistor on.
Or could be the comparators (U106) turning on U107 and then turning on the audio.
Or could be a short or other problem on the traces from U104, U105 outputs into the comparators inputs. Ensure Pins 3 & 5 are lower than the references pins 2 & 6.


Current draw with the Audio Beeping is about 150mA. With no sound the current draw should be closer to 50-60mA.

[waleed]

Waltr, I was adding a pot from TR2 collector to the ground for volume control (I saw you posted that somewhere in the forum),and when I removed it the heating problem is gone and the current becomes like 40mA with coil connected, are you sure you have a volume control connected like this way?, and tomorrow I'll buy a new ICs which I have removed and will see what would happen.