I picked up a KR-5400 as another learning project and boy am I learning a lesson.
When I picked it up it was fully working with the exception of dirty controls and a few lamps out. I replaced the lamps with LED's and cleaned the controls and it was a great working little unit. Had it set up on the listening table for a couple of weeks and no issues.
When the parts arrived I started with a recap of the PS board and I replaced the main filter caps with 10,000uf units. At each step I powered it up and checked the protection relay to make sure it engaged. I continued on with the recap of the amp board and the tone control board again verifying powerup and relay engagement.
After getting this far and before tackling transistors I thought I'd give it a listen. That's where I ran into problems. The unit still powers up and the relay still engages, but when I increase the volume slightly I get a little amplitude on the left channel, but none on the right. By the time the volume hits 9 o'clock the protection relay disengages. I was pretty bummed last night, but now I have my first opportunity to troubleshoot a non working unit.
It took awhile to find the correct service manual with the correct diagrams, but I would up buying it from Analog Alley. It is watermarked and there are instructions not to share, but I don't see how one can claim rights on a 50 year old document that one didn't produce, so I'm happy to share my copy with anyone that needs it.
I started my troubleshooting with visually inspecting for solder bridges, backwards caps and bad solders and found none. Still a possibility, but I looked through it good a couple of times.
Next I began to check voltages at the PS board and found a few issues.
Pin 7 should be 24.5v and it reads -.038v.
Pin 10 should be 24.5v and it reads -.037v.
Pin 14 should be 7v and it reads -.006v.
Also
Pin 6 should be -35v and it reads -27.96v
Pin 9 should be 35v and it reads 27.78v.
I took the main filter caps out of circuit which seems to eliminate the amp board and the voltage measurements remain the same.
I'm wondering what the next step should be. I'm worried that the transformer isn't working correctly and was thinking about removing the wires from the transformer to the power supply and testing the voltage taps while disconnected, but maybe there is an issue in the power supply board or with the rectifier?
I "think" I eliminated the amp board, but I suppose there could be multiple issues.
Happy to share any pics requested before I start removing the transformer.
Thanks for the community!
When I picked it up it was fully working with the exception of dirty controls and a few lamps out. I replaced the lamps with LED's and cleaned the controls and it was a great working little unit. Had it set up on the listening table for a couple of weeks and no issues.
When the parts arrived I started with a recap of the PS board and I replaced the main filter caps with 10,000uf units. At each step I powered it up and checked the protection relay to make sure it engaged. I continued on with the recap of the amp board and the tone control board again verifying powerup and relay engagement.
After getting this far and before tackling transistors I thought I'd give it a listen. That's where I ran into problems. The unit still powers up and the relay still engages, but when I increase the volume slightly I get a little amplitude on the left channel, but none on the right. By the time the volume hits 9 o'clock the protection relay disengages. I was pretty bummed last night, but now I have my first opportunity to troubleshoot a non working unit.
It took awhile to find the correct service manual with the correct diagrams, but I would up buying it from Analog Alley. It is watermarked and there are instructions not to share, but I don't see how one can claim rights on a 50 year old document that one didn't produce, so I'm happy to share my copy with anyone that needs it.
I started my troubleshooting with visually inspecting for solder bridges, backwards caps and bad solders and found none. Still a possibility, but I looked through it good a couple of times.
Next I began to check voltages at the PS board and found a few issues.
Pin 7 should be 24.5v and it reads -.038v.
Pin 10 should be 24.5v and it reads -.037v.
Pin 14 should be 7v and it reads -.006v.
Also
Pin 6 should be -35v and it reads -27.96v
Pin 9 should be 35v and it reads 27.78v.
I took the main filter caps out of circuit which seems to eliminate the amp board and the voltage measurements remain the same.
I'm wondering what the next step should be. I'm worried that the transformer isn't working correctly and was thinking about removing the wires from the transformer to the power supply and testing the voltage taps while disconnected, but maybe there is an issue in the power supply board or with the rectifier?
I "think" I eliminated the amp board, but I suppose there could be multiple issues.
Happy to share any pics requested before I start removing the transformer.
Thanks for the community!
