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TR5 Help

 

I am waiting for a new BFO crystal for my TR7 so in the meantime I am working on my TR5. The 10 volt power supply failed when I turned it on a?week or so ago. I have checked just about everything I can on the board. I have replaced the 723 regulator chip and a couple transistors and checked diodes etc. The problem seems to be that the adjustment?pot does not adjust the output voltage at all. I am at 7.21 volts and can't seem to change it any. I have added a blown up section of the schematic for the circuit. Many thanks for any comments.

73, Jim VE1RB

TR5PowerSupply.pdf
TR5PowerSupply.pdf

 

Jim, what is the voltage on pin 4, and does it vary at all with the pot? What is the voltage on pins 10 and 11? Is the pass transistor getting warm at all?
?
Dave
 

Hi Dave. The voltage on pin 4 is 7.20 VDC and no it does not change turning the 10 volt adjust pot. Pins 11 and 12 both have 13.68 VDC and Pin 10 has 5.397. No transistors get warm or hot. Does that help?

73, Jim VE1RB

On Wed, Jan 22, 2025 at 11:14?AM Dave W7GZ via <w7gz=[email protected]> wrote:
Jim, what is the voltage on pin 4, and does it vary at all with the pot? What is the voltage on pins 10 and 11? Is the pass transistor getting warm at all?
?
Dave
 

Jim, is the voltage on pin 5 also 7.2V? At 7.21V output, the voltage on pin 10 should be around 5.05V and you have 5.3V. Is Q404 good? What is the voltage B-E on it? How about the voltage on its collector?
?
You replaced the regulator with a known good new one? Dave
 

Jim, the fact that the voltage on pin 4 does not change at all bothers me. There should be a volt or two swing with the pot. It makes me think its divider network is open somehow. Check the resistors and that diode should have a 0.7V drop across it. The voltage at each junction in the divider network should NOT be 7.20V.
?
Dave
 

Dave I just measured the Base to Emitter voltage on Q404 and it is 7.92. I think I found a problem as it seems that the diode is not connected to the pot. I am going to remove the board again and check on the bottom. Will get back to you after I do that. Also here is the same scan with voltages written on it. Again I thank you so much for your time and help.

73, JimVE1RB

On Wed, Jan 22, 2025 at 12:39?PM Dave W7GZ via <w7gz=[email protected]> wrote:
Jim, the fact that the voltage on pin 4 does not change at all bothers me. There should be a volt or two swing with the pot. It makes me think its divider network is open somehow. Check the resistors and that diode should have a 0.7V drop across it. The voltage at each junction in the divider network should NOT be 7.20V.
?
Dave

TR5PowerSypplyReadings.pdf
TR5PowerSypplyReadings.pdf

 

Hi Dave. Just wanted to let you know that was the problem as I now have 10.00 VDC although I will check it at the back panel as they say to do in the manual. I don't know why I did not see that earlier. Guess I couldn't see the trees for the forest hi hi. I really appreciate your help. Now maybe I can start work again on trying to get the transmitter working. I initially?had a bad output transistor so bought a matched pair and replaced?them but it still did not work. Then I found a bad transmitter mixer transistor and a burnt?resistor?as the transistor had a collector to Base short and it did the resistor in. Replaced the transistor and the resistor and that one failed and it was the same part number. So have go back and check that out. I noticed I down't have hardly any audio in the speaker too. Lots to keep me busy. Thanks again Dave.

74, Jim VE1RB

On Wed, Jan 22, 2025 at 1:45?PM Jim Harris <radiove1rb@...> wrote:
Dave I just measured the Base to Emitter voltage on Q404 and it is 7.92. I think I found a problem as it seems that the diode is not connected to the pot. I am going to remove the board again and check on the bottom. Will get back to you after I do that. Also here is the same scan with voltages written on it. Again I thank you so much for your time and help.

73, JimVE1RB

On Wed, Jan 22, 2025 at 12:39?PM Dave W7GZ via <w7gz=[email protected]> wrote:
Jim, the fact that the voltage on pin 4 does not change at all bothers me. There should be a volt or two swing with the pot. It makes me think its divider network is open somehow. Check the resistors and that diode should have a 0.7V drop across it. The voltage at each junction in the divider network should NOT be 7.20V.
?
Dave
 

Good job, Jim, I'm happy you solved it with no further defective parts. Keep the group posted on your progress.
?
Dave
 

Will do Dave.?

Jim VE1RB

On Wed, Jan 22, 2025 at 2:38?PM Dave W7GZ via <w7gz=[email protected]> wrote:
Good job, Jim, I'm happy you solved it with no further defective parts. Keep the group posted on your progress.
?
Dave

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