Thanks Mike 
Like you, I'm beginning to suspect a hidden crack in the print somewhere. Maybe on both his boards.
If you have 34 volts (AC) on the transformer wires then you must also have that 34 volts AC on the bridge because the wires go directly there. If there is nothing on the bridge (no 34 volts AC input) then there has to be a break, or, unlikely, a dead short..
Edit.. I just seen where you say 'the transformer gets very hot very fast'. That does point to a short circuit which can really only be the bridge rectifier, a solder blob or accidental short on the board. A short across either C2 or C3 would also cause that.
Depending in the wattage of R9 and R10 and the current capacity of the transformer its possible the overload could be via the output transistors. You can easily check that by removing R10 and R6 and seeing if the voltage comes up.
Like you, I'm beginning to suspect a hidden crack in the print somewhere. Maybe on both his boards.If you have 34 volts (AC) on the transformer wires then you must also have that 34 volts AC on the bridge because the wires go directly there. If there is nothing on the bridge (no 34 volts AC input) then there has to be a break, or, unlikely, a dead short..
Edit.. I just seen where you say 'the transformer gets very hot very fast'. That does point to a short circuit which can really only be the bridge rectifier, a solder blob or accidental short on the board. A short across either C2 or C3 would also cause that.
Depending in the wattage of R9 and R10 and the current capacity of the transformer its possible the overload could be via the output transistors. You can easily check that by removing R10 and R6 and seeing if the voltage comes up.
The board layout in post #1 (that's the two bridge circuit) and the circuit diagram you posted a bit later are different in detail which makes quoting reference numbers meaningless.
You start on this one by checking the basics. Is the total supply voltage correct ? That's the DC voltage from C2 negative to C3 positive. Have you got your 40 volts or thereabouts present.
If not then you need to find why. Is it being pulled down by a fault or short. The only thing that could do that would be the AD149's being turned on. Removing R10 and what is shown as R6 (120 ohm) on the diagram... it may not be on that reference on the two bridge circuit would isolate the output stage.
I think to be honest you are not understanding the basic principles of how the voltages are derived and how to test for shorts and open circuits.
You start on this one by checking the basics. Is the total supply voltage correct ? That's the DC voltage from C2 negative to C3 positive. Have you got your 40 volts or thereabouts present.
If not then you need to find why. Is it being pulled down by a fault or short. The only thing that could do that would be the AD149's being turned on. Removing R10 and what is shown as R6 (120 ohm) on the diagram... it may not be on that reference on the two bridge circuit would isolate the output stage.
I think to be honest
you are not understanding the basic principles of how the voltages are derived and how to test for shorts and open circuits.I power on now PCB 1bridge version.
It's very strange. 1st minute it's working and has stable 5V AC on the 33 speed then It suddenly drops to the 0.6V AC and the buld lights very brightly. Then after some time it could go to 5V AC again and the motor begin to rotate. Something making it on working-notworking state. Mystery.
It's very strange. 1st minute it's working and has stable 5V AC on the 33 speed then It suddenly drops to the 0.6V AC and the buld lights very brightly. Then after some time it could go to 5V AC again and the motor begin to rotate. Something making it on working-notworking state. Mystery.
I have not read the entire thread, but if the board is O.K. (no cracks and all tracks measure O.K.), in my experience with the TD125, first to check is:
the bridge rectifier and the two big electrolytic capacitors of the power supply.
These components sometimes develop a short circuit.
Observe the right polarity when replacing these elco's.
Also, carefully clean the PCB pads of the speed selector with a glass fibre brush.
Greetings, 968driver.
the bridge rectifier and the two big electrolytic capacitors of the power supply.
These components sometimes develop a short circuit.
Observe the right polarity when replacing these elco's.
Also, carefully clean the PCB pads of the speed selector with a glass fibre brush.
Greetings, 968driver.
that's no problem,lets see what we can do......That sounds like either a physical fault (break in print) or something going faulty under load or when voltage is applied. Do any of the transistors or rectifiers get hot when it does this ?
Thanks
There is nothing like practical experience of typical faults. His second board sounds very much like there is a short around the rectifier. Up to a point yes. If it reads short circuit across any of the four pins then its faulty.
With a (digital) multimeter switched to the "diode" position, measure between "AC" and "+", and "AC" and "-" leads of the bridge rectifier. Do this for both "AC" terminals of the bridge rectifier. These measurements should read about 0,7 in one direction, and no conduction in the other direction.
Between the "AC" terminals you measure the rather low resistance of the transformer secundary.
Between the "AC" terminals you measure the rather low resistance of the transformer secundary.
Something is wrong on this bridge. I have a broken PCB where I have the same bridge rectifie. I put my DVM on the diode check. Reading of the good bridge:
1. Red wire on the "minus" of the bridge black wire on the first "~" mark of the bridge - 0.67V
2. Reverse wires - infinity
3. Red wire on the "minus" of the bridge black wire on the second "~" mark of the bridge - 0.67V
4. Reverse wires - infinity
5. Black wire on the "+" of the bridge black wire on the first "~" mark of the bridge - 0.67V
6. Reverse wires - infinity
7. Black wire on the "+" of the bridge black wire on the second "~" mark of the bridge - 0.67V
8. Reverse wires - infinity
So the bridge is OK.
On this PCB readings are absolutely strange:
1. Red wire on the "minus" of the bridge black wire on the first "~" mark of the bridge - 0.089V
2. Reverse wires - 0.860Vhttp://www.lingvo-online.ru/ru/Sear...ь&translation=infinity&srcLang=ru&destLang=en
3. Red wire on the "minus" of the bridge black wire on the second "~" mark of the bridge - 0.089V
4. Reverse wires - 0.860V
5. Black wire on the "+" of the bridge black wire on the first "~" mark of the bridge - 0.08V
6. Reverse wires - infinityhttp://www.lingvo-online.ru/ru/Sear...ь&translation=infinity&srcLang=ru&destLang=en
7. Black wire on the "+" of the bridge black wire on the second "~" mark of the bridge - 0.08V
8. Reverse wires - infinity
1. Red wire on the "minus" of the bridge black wire on the first "~" mark of the bridge - 0.67V
2. Reverse wires - infinity
3. Red wire on the "minus" of the bridge black wire on the second "~" mark of the bridge - 0.67V
4. Reverse wires - infinity
5. Black wire on the "+" of the bridge black wire on the first "~" mark of the bridge - 0.67V
6. Reverse wires - infinity
7. Black wire on the "+" of the bridge black wire on the second "~" mark of the bridge - 0.67V
8. Reverse wires - infinity
So the bridge is OK.
On this PCB readings are absolutely strange:
1. Red wire on the "minus" of the bridge black wire on the first "~" mark of the bridge - 0.089V
2. Reverse wires - 0.860Vhttp://www.lingvo-online.ru/ru/Sear...ь&translation=infinity&srcLang=ru&destLang=en
3. Red wire on the "minus" of the bridge black wire on the second "~" mark of the bridge - 0.089V
4. Reverse wires - 0.860V
5. Black wire on the "+" of the bridge black wire on the first "~" mark of the bridge - 0.08V
6. Reverse wires - infinityhttp://www.lingvo-online.ru/ru/Sear...ь&translation=infinity&srcLang=ru&destLang=en
7. Black wire on the "+" of the bridge black wire on the second "~" mark of the bridge - 0.08V
8. Reverse wires - infinity
The only thing that could draw current enough to pull the voltage down are the two AD149's. Isolate R10 and the base of T6 and they are all isolated from the circuit.
Readings on the 2nd PCB with 2bridges also little strange.
1st bridge (seems to be perfect):
1. Red wire on the "minus" of the bridge black wire on the first "~" mark of the bridge - 0.67V
2. Reverse wires - infinity
3. Red wire on the "minus" of the bridge black wire on the second "~" mark of the bridge - 0.67V
4. Reverse wires - infinity
5. Black wire on the "+" of the bridge black wire on the first "~" mark of the bridge - 0.67V
6. Reverse wires - infinity
7. Black wire on the "+" of the bridge black wire on the second "~" mark of the bridge - 0.67V
8. Reverse wires - infinity
2nd bridge:
1. Red wire on the "minus" of the bridge black wire on the first "~" mark of the bridge - 0.67V
2. Reverse wires - 0.67V
3. Red wire on the "minus" of the bridge black wire on the second "~" mark of the bridge - 0.67V
4. Reverse wires - 0.67V
5. Black wire on the "+" of the bridge black wire on the first "~" mark of the bridge - 0.67V
6. Reverse wires - 0.67V
7. Black wire on the "+" of the bridge black wire on the second "~" mark of the bridge - 0.67V
8. Reverse wires - 0.67V
1st bridge (seems to be perfect):
1. Red wire on the "minus" of the bridge black wire on the first "~" mark of the bridge - 0.67V
2. Reverse wires - infinity
3. Red wire on the "minus" of the bridge black wire on the second "~" mark of the bridge - 0.67V
4. Reverse wires - infinity
5. Black wire on the "+" of the bridge black wire on the first "~" mark of the bridge - 0.67V
6. Reverse wires - infinity
7. Black wire on the "+" of the bridge black wire on the second "~" mark of the bridge - 0.67V
8. Reverse wires - infinity
2nd bridge:
1. Red wire on the "minus" of the bridge black wire on the first "~" mark of the bridge - 0.67V
2. Reverse wires - 0.67V
3. Red wire on the "minus" of the bridge black wire on the second "~" mark of the bridge - 0.67V
4. Reverse wires - 0.67V
5. Black wire on the "+" of the bridge black wire on the first "~" mark of the bridge - 0.67V
6. Reverse wires - 0.67V
7. Black wire on the "+" of the bridge black wire on the second "~" mark of the bridge - 0.67V
8. Reverse wires - 0.67V
Last edited:
R10 and T6 T7 bases isolated
Readings changed from:
1. Red wire on the "minus" of the bridge black wire on the first "~" mark of the bridge - 0.089V
2. Reverse wires - 0.860V
3. Red wire on the "minus" of the bridge black wire on the second "~" mark of the bridge - 0.089V
4. Reverse wires - 0.860V
5. Black wire on the "+" of the bridge black wire on the first "~" mark of the bridge - 0.08V
6. Reverse wires - infinity
7. Black wire on the "+" of the bridge black wire on the second "~" mark of the bridge - 0.08V
8. Reverse wires - infinity
to
1. Red wire on the "minus" of the bridge black wire on the first "~" mark of the bridge - 0.67V
2. Reverse wires - 0.860V
3. Red wire on the "minus" of the bridge black wire on the second "~" mark of the bridge - 0.67V
4. Reverse wires - 0.860V
5. Black wire on the "+" of the bridge black wire on the first "~" mark of the bridge - 0.67V
6. Reverse wires - infinity
7. Black wire on the "+" of the bridge black wire on the second "~" mark of the bridge - 0.67V
8. Reverse wires - infinity
What is it?
Readings changed from:
1. Red wire on the "minus" of the bridge black wire on the first "~" mark of the bridge - 0.089V
2. Reverse wires - 0.860V
3. Red wire on the "minus" of the bridge black wire on the second "~" mark of the bridge - 0.089V
4. Reverse wires - 0.860V
5. Black wire on the "+" of the bridge black wire on the first "~" mark of the bridge - 0.08V
6. Reverse wires - infinity
7. Black wire on the "+" of the bridge black wire on the second "~" mark of the bridge - 0.08V
8. Reverse wires - infinity
to
1. Red wire on the "minus" of the bridge black wire on the first "~" mark of the bridge - 0.67V
2. Reverse wires - 0.860V
3. Red wire on the "minus" of the bridge black wire on the second "~" mark of the bridge - 0.67V
4. Reverse wires - 0.860V
5. Black wire on the "+" of the bridge black wire on the first "~" mark of the bridge - 0.67V
6. Reverse wires - infinity
7. Black wire on the "+" of the bridge black wire on the second "~" mark of the bridge - 0.67V
8. Reverse wires - infinity
What is it?
I'm talking about the 1st pcb 1bridge version where there is good voltage across C2/C3
now here R10 T6 T7 isolated. I have readings:
R10 and T6 T7 bases isolated
Readings changed from:
1. Red wire on the "minus" of the bridge black wire on the first "~" mark of the bridge - 0.089V
2. Reverse wires - 0.860V
3. Red wire on the "minus" of the bridge black wire on the second "~" mark of the bridge - 0.089V
4. Reverse wires - 0.860V
5. Black wire on the "+" of the bridge black wire on the first "~" mark of the bridge - 0.08V
6. Reverse wires - infinity
7. Black wire on the "+" of the bridge black wire on the second "~" mark of the bridge - 0.08V
8. Reverse wires - infinity
to
1. Red wire on the "minus" of the bridge black wire on the first "~" mark of the bridge - 0.67V
2. Reverse wires - 0.860V
3. Red wire on the "minus" of the bridge black wire on the second "~" mark of the bridge - 0.67V
4. Reverse wires - 0.860V
5. Black wire on the "+" of the bridge black wire on the first "~" mark of the bridge - 0.67V
6. Reverse wires - infinity
7. Black wire on the "+" of the bridge black wire on the second "~" mark of the bridge - 0.67V
8. Reverse wires - infinity
now here R10 T6 T7 isolated. I have readings:
R10 and T6 T7 bases isolated
Readings changed from:
1. Red wire on the "minus" of the bridge black wire on the first "~" mark of the bridge - 0.089V
2. Reverse wires - 0.860V
3. Red wire on the "minus" of the bridge black wire on the second "~" mark of the bridge - 0.089V
4. Reverse wires - 0.860V
5. Black wire on the "+" of the bridge black wire on the first "~" mark of the bridge - 0.08V
6. Reverse wires - infinity
7. Black wire on the "+" of the bridge black wire on the second "~" mark of the bridge - 0.08V
8. Reverse wires - infinity
to
1. Red wire on the "minus" of the bridge black wire on the first "~" mark of the bridge - 0.67V
2. Reverse wires - 0.860V
3. Red wire on the "minus" of the bridge black wire on the second "~" mark of the bridge - 0.67V
4. Reverse wires - 0.860V
5. Black wire on the "+" of the bridge black wire on the first "~" mark of the bridge - 0.67V
6. Reverse wires - infinity
7. Black wire on the "+" of the bridge black wire on the second "~" mark of the bridge - 0.67V
8. Reverse wires - infinity
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