I'd check all 3 while you're in there. Caps are probably going or gone as well at this age, or especially if there was any excessive heat around them.
Troubleshooting Help: Tandberg TR-2080
- Thread starter kohlmeyer
- Start date
I received a shipment of parts today. I haven’t received the BC550C transistors yet, but I had preemptively ordered a number of capacitors to have on stand-by and some BC549C’s, before getting advised of the better, alternative transistor.
For better or worse, I went ahead and replaced the bad Q604 with a new BC549C. In doing so, the receiver regained much of its normal operation.
Issues still remain, however. Upon power-up, when monitoring the voltage of R615, voltage is very slow to rise. Timing it now, it takes 1:53 to make it to 25V. It spends most of that time around 8-10V. While climbing, FM is very unstable and reception walks all over the place. When it reaches ~25V it becomes much more stable and accurate. Though, once at around ~25V, it will slowly and sporadically deviate between about 24.6V up to ~25.7V. When it does, this causes tuning to drift a little.
With this additional information, should I remove/check/replace the other transistor, Q605? Or should attention move elsewhere?
For better or worse, I went ahead and replaced the bad Q604 with a new BC549C. In doing so, the receiver regained much of its normal operation.
Issues still remain, however. Upon power-up, when monitoring the voltage of R615, voltage is very slow to rise. Timing it now, it takes 1:53 to make it to 25V. It spends most of that time around 8-10V. While climbing, FM is very unstable and reception walks all over the place. When it reaches ~25V it becomes much more stable and accurate. Though, once at around ~25V, it will slowly and sporadically deviate between about 24.6V up to ~25.7V. When it does, this causes tuning to drift a little.
With this additional information, should I remove/check/replace the other transistor, Q605? Or should attention move elsewhere?
Did you check all 3?
Just 2, as of now.
I pulled Q603 and Q604. I replaced Q604 because it tested bad. Am I able to accurately test Q605 while it is mounted? If not, should I go ahead and replace Q605 if I have to pull it anyway?
You should be able to see if it's good while installed. I'd replace the electrolytics in the area as well.
Wouldn't hurt to scrub the regulator pot a bit, R616. That adjusts the +25 volts.
Ray Gianelli,
I tested the last remaining transistor - Q605 - as it was seated on the board. There were some peculiarities about some of the values I was getting; namely, there was evidence of voltage-drop across all legs and in all manners of testing (+,- vs -,+). I went ahead and removed the transistor to test out of circuit and had similar results. Once replaced with a new transistor, everything seems to work as it should!
Voltage on R615 hit +24.6V about as quickly as it takes for the speaker relay to engage. FM tuning is stable and accurate. Sound is great. I was able to finely attenuate the voltage using the regulator pot and it now sticks to +25.0V.
Thank you so much for your time, patience, and knowledge. I really appreciate the help from you and from everyone in the AK community that stopped-by to share input and insight.
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Love to hear a success story. Good job getting her going!