I am trying to repair a Tandberg TR2055 receiver. I have repaired several Tandberg receivers but this one has me stumped. I'm guessing that I am overlooking something obvious.
It arrived in non-working condition and obviously someone had done some work to it previously. I replaced all the electrolytic capacitors because Tandberg used Frako caps that are notorious for becoming leaky.
The problem: I'm getting almost the full positive rail voltage at the outputs and the base and emitter of the outputs. I'm getting about 26vdc at the input.
Both channels exhibit the exact same problem.
I have removed and checked each component on the board. I used a Peak DCA55 to test transistors and diodes. The only problem I could find were:
- The differential pair (Q801/803 and Q802/804) is a 2SC1583 (2 NPN transistors in a common case, with emitters joined). The Hfe on each pair was not closely matched (540/380 and 470/338)
- Both Q807 and Q808 are BD530. These showed as common cathode on my DCA55 but apparently this can be caused by very low gain. There are 2 other BD530s in the circuit and they tested normal on the DCA55.
I'm attaching a scan of the schematic for this amp board. Because both boards are exhibiting the same exact problem, I feel it must be something common to each. Since it had been hacked up previously, I've been trying to locate something done wrong but no luck.
I've spent way more time than this receiver is worth but I would sure like to know what I am missing. Any suggestions will be greatly appreciated.
It arrived in non-working condition and obviously someone had done some work to it previously. I replaced all the electrolytic capacitors because Tandberg used Frako caps that are notorious for becoming leaky.
The problem: I'm getting almost the full positive rail voltage at the outputs and the base and emitter of the outputs. I'm getting about 26vdc at the input.
Both channels exhibit the exact same problem.
I have removed and checked each component on the board. I used a Peak DCA55 to test transistors and diodes. The only problem I could find were:
- The differential pair (Q801/803 and Q802/804) is a 2SC1583 (2 NPN transistors in a common case, with emitters joined). The Hfe on each pair was not closely matched (540/380 and 470/338)
- Both Q807 and Q808 are BD530. These showed as common cathode on my DCA55 but apparently this can be caused by very low gain. There are 2 other BD530s in the circuit and they tested normal on the DCA55.
I'm attaching a scan of the schematic for this amp board. Because both boards are exhibiting the same exact problem, I feel it must be something common to each. Since it had been hacked up previously, I've been trying to locate something done wrong but no luck.
I've spent way more time than this receiver is worth but I would sure like to know what I am missing. Any suggestions will be greatly appreciated.
No, I'm getting 22 volts at the signal side of the input connector - J807. And about 20 volts at the shield side of that same connector. I'm getting about 35vdc at the emitter of Q801/803.
No it did not work before recapping. Which makes it more difficult for me to resolve.
The fuses on both channels were blown and one of the outputs on the right side was blown also. I replaced both outputs on the right side with MJE15003/MJE15004.
D815 is functioning correctly and installed with correct orientation. Interestingly, I get positive 38 vdc on the cathode side and negative 37 vdc on the anode side of this diode.
I get negative 5.73 vdc at the anode side of D801. But it's the cathode that's connected to ground in my schematic. The schematic indicates there should be negative 15 v at that point.
I wondered if it might be a ground issue, but not sure where to find it. That would account for both channels having the same problem.
I thought I'd report back on the solution of the problem.
First I located a solder bridge between base and emitter on Q803. But that didn't solve the problem. Q807/808 were showing as "common cathode diodes" on my Altas DCA55 tester. So I replaced these with MJE253 and all is well.
Thanks for the assistance with this one!
First I located a solder bridge between base and emitter on Q803. But that didn't solve the problem. Q807/808 were showing as "common cathode diodes" on my Altas DCA55 tester. So I replaced these with MJE253 and all is well.
Thanks for the assistance with this one!
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