Needed: SONY TA-1120F Schematic or service manual

How is it possible that a model can be made for several years by a huge corporation and nobody seems to have a service manual or schematic for the Sony TA-1120F - this is the third version of the TA1120 that uses FETs in the preamp and has a completely different power amp section.

Even if it sold only in Japan, you would like to believe that at least one person who worked at Sony or in a service outlet might have one usable copy and be a member of an audio related on-line social group.

I have received a unit that has a functional power amp but has a problem in the Line stage that causes one of the main filter cap voltages to raise up about 30vdc from about 50v to about 80v and causes the other filter cap to decrease by about 30v from about 50v to 20v. I have found that when the B+ is disconnected from the line stage (but not the phono stage or tone control boards) that the voltages remain correct and stable. When I apply the B+ to the line stage board, it causes the 30v shifts.

It would be great to find a schematic...

Does anyone have pictures of the back sides of the three preamp boards that they can share that shows where the wiring is attached to the traces?

I have not pulled all of the transistors from the line board (the middle of the three boards) but I have done some in circuit ohm and diode tests and nothing seems wrong. I received this unit following someone elses attempted repair and I am wondering if they have placed a wire on the wrong trace. I really hate having to reverse engineer this unit, but it sure looks like that is where this is headed.

Can anyone help? No need to reply if you have no idea or no experience with this model.

Thank you!
 
Last edited:

Mooly

Administrator
Paid Member
2007-09-15 8:14 am
Can't help with a manual but the fault you describe could possibly be an open ground somewhere, even something as obscure as the transformer assuming it uses a conventional PSU.

Are you measuring these cap voltages directly across the parts concerned or are you measuring from somewhere you think should be ground... and I'm just guessing but this is how I would begin to approach this.