poortom
Active Member
A follow up on my CR-2020 recap job and power transistor replacement. Now I have a new PS problem.
I replaced all four output transistors and finished recapping the power amp boards. I now have them reinstalled. I had previously installed the two output transistors in reverse locations in one of the boards, taking the original transistors out.
I did a burn-in the other night and everything seemed fine. Yesterday morning, the protection relay kicked in after about a half hour. Now it kicks in a minute or two after power-up. (Give or take)
The +- 40v (Or so) lines coming of the cap board look steady at first. Then after a few minutes, they start to rise together to +- 46volts or higher at times (The -40 gets more negative). At the same time these voltages are rising, the +-25 volt lines each drop (the -25 gets less negative) steadily at about the same rate. The protection relay drops out when they get to around +-18 volts respectively.
All I can figure is the +- 25 volt lines mostly powers the preamp circuit boards. I have not removed or messed with them yet. I can’t see what would be pulling or causing those voltages to drop together at the same rate.
What’s common to these +/ 25 other than the rectifier and caps back on the cap board? What would explain the incoming voltages to rise and the outgoing voltage to drop? Is it that the +-40 lines unloading?
This power supply board is kind of a mess. A lot of tracers were burned when I first got this unit. I’ve tried my best to repair them. I went through and re-soldered the 8 transistors having to do with these circuits. I did most of this repair work a couple of years ago and had it working pretty well before I started my recent recap job.
The 6 pin connector was replaced a couple of years ago and is pretty good yet. I recently installed a new protection relay.
I am a trained technician from many years ago but have never done much board-level troubleshooting work. Please bear with me!
Thanks, Tom
I replaced all four output transistors and finished recapping the power amp boards. I now have them reinstalled. I had previously installed the two output transistors in reverse locations in one of the boards, taking the original transistors out.
I did a burn-in the other night and everything seemed fine. Yesterday morning, the protection relay kicked in after about a half hour. Now it kicks in a minute or two after power-up. (Give or take)
The +- 40v (Or so) lines coming of the cap board look steady at first. Then after a few minutes, they start to rise together to +- 46volts or higher at times (The -40 gets more negative). At the same time these voltages are rising, the +-25 volt lines each drop (the -25 gets less negative) steadily at about the same rate. The protection relay drops out when they get to around +-18 volts respectively.
All I can figure is the +- 25 volt lines mostly powers the preamp circuit boards. I have not removed or messed with them yet. I can’t see what would be pulling or causing those voltages to drop together at the same rate.
What’s common to these +/ 25 other than the rectifier and caps back on the cap board? What would explain the incoming voltages to rise and the outgoing voltage to drop? Is it that the +-40 lines unloading?
This power supply board is kind of a mess. A lot of tracers were burned when I first got this unit. I’ve tried my best to repair them. I went through and re-soldered the 8 transistors having to do with these circuits. I did most of this repair work a couple of years ago and had it working pretty well before I started my recent recap job.
The 6 pin connector was replaced a couple of years ago and is pretty good yet. I recently installed a new protection relay.
I am a trained technician from many years ago but have never done much board-level troubleshooting work. Please bear with me!
Thanks, Tom
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