Hi
Got the Technics SU-v4x amp as spares or repair. Fancied a challenege to see if I could fix it as I like them. Seller said it was working until it started going into protection from time to time but now full time.
Burned a cap C523 as soon as I plugged it in > replaced it > OK
Checked the pre drive transistors Q501 - 4 >OK
Checked for cold solder joints > nothing yet
Input selector does not work properly as it does not show red led selection. Only the yellow tape source selection.
Track on circuit board had been previously repaired. Cheked it
Eventually I got it out of protection mode by replacing C523 and R535 which had also blown. Also replaced relay as it was stuck.
The input selector still does not work properly - only the tape select works so no sound. I think it is a power supply issue but cannot work out what to do next.
The 50v rails are fine but the issue is with the 15v rail which supplies the various tone / selector / phono pre amp boards via jumpers is running at 1.89 volts.
All the Q701 - 5 regulator transistors seem to be OK (Not checked Q705 yet). The 4 rectifier diodes are OK I think with 2 showing 50v in one direction and the other two showing the same in the opposite direction.
I feel I am on the cusp of kind of fixing it or maybe not as it may just go into protection mode again if I get the 15v rail back!
Any help would be appreciated. Attached is the service manual.
Got the Technics SU-v4x amp as spares or repair. Fancied a challenege to see if I could fix it as I like them. Seller said it was working until it started going into protection from time to time but now full time.
Burned a cap C523 as soon as I plugged it in > replaced it > OK
Checked the pre drive transistors Q501 - 4 >OK
Checked for cold solder joints > nothing yet
Input selector does not work properly as it does not show red led selection. Only the yellow tape source selection.
Track on circuit board had been previously repaired. Cheked it
Eventually I got it out of protection mode by replacing C523 and R535 which had also blown. Also replaced relay as it was stuck.
The input selector still does not work properly - only the tape select works so no sound. I think it is a power supply issue but cannot work out what to do next.
The 50v rails are fine but the issue is with the 15v rail which supplies the various tone / selector / phono pre amp boards via jumpers is running at 1.89 volts.
All the Q701 - 5 regulator transistors seem to be OK (Not checked Q705 yet). The 4 rectifier diodes are OK I think with 2 showing 50v in one direction and the other two showing the same in the opposite direction.
I feel I am on the cusp of kind of fixing it or maybe not as it may just go into protection mode again if I get the 15v rail back!
Any help would be appreciated. Attached is the service manual.
Attachments
-
5.8 MB Views: 19