colklink77
New Member
Hello, all
I have lurked here for a while, but this is my first thread. I've started getting into restoring old receivers as a hobby (IT is my profession). I've mostly stuck to pioneer stuff, but a Kenwood KR-7050 caught my eye on ebay for a fair price, so I picked it up. It was advertised as having the right channel out.
When it arrived, I popped the cover off, and found that someone else had already attempted to repair the issue, but didn't seem to have much luck. It looks like the X00-2050-10 power supply board had gotten hot and cooked some components. The board is black right under R4. It looks like to try to resolve the issue, Q2, Q4, R6, R4, R8, D4 and the PNP and NPN power output transistors were replaced. It appears from what I've read on here that Q2 and Q4 were replaced with the wrong transistors (C4793, and A1837), and the Toshiba 2SA1095 and 2SC2595 appear to be counterfeits. I've ordered the correct transistors (15032G and 15033G for Q2 and Q4, and Sanken 2SA1215 and 2sc2921 to replace the Toshibas). However, I would like to try to resolve the initial issue before I plug in new parts and potentially cook them as well.
I cleaned up some poor soldering, tested the 2SA1215 and 2SC2921 with a multimeter (is there a better way to test them?) and tested any components in that circuit that I could. If i plug in the Toshiba power transistors, I do not get a relay click in the protection circuit. If I unplug them, the click of the relay does happen. It also appears that the spot is still getting warm on the board in the same spot. I do have it hooked to a dim bumb tester, so it may be preventing it from cooking as hot as it did before.
Any ideas from the expert? At this stage, I'm just a parts replacer and still trying to wrap my head around reading circuits and diagnosing them at that level. The only service manuals I could find are also barely legible, when it comes to the voltage values on components, so that doesn't help either...
I've attached a photo of the problem area. Sorry for the wall of text and thanks!
I have lurked here for a while, but this is my first thread. I've started getting into restoring old receivers as a hobby (IT is my profession). I've mostly stuck to pioneer stuff, but a Kenwood KR-7050 caught my eye on ebay for a fair price, so I picked it up. It was advertised as having the right channel out.
When it arrived, I popped the cover off, and found that someone else had already attempted to repair the issue, but didn't seem to have much luck. It looks like the X00-2050-10 power supply board had gotten hot and cooked some components. The board is black right under R4. It looks like to try to resolve the issue, Q2, Q4, R6, R4, R8, D4 and the PNP and NPN power output transistors were replaced. It appears from what I've read on here that Q2 and Q4 were replaced with the wrong transistors (C4793, and A1837), and the Toshiba 2SA1095 and 2SC2595 appear to be counterfeits. I've ordered the correct transistors (15032G and 15033G for Q2 and Q4, and Sanken 2SA1215 and 2sc2921 to replace the Toshibas). However, I would like to try to resolve the initial issue before I plug in new parts and potentially cook them as well.
I cleaned up some poor soldering, tested the 2SA1215 and 2SC2921 with a multimeter (is there a better way to test them?) and tested any components in that circuit that I could. If i plug in the Toshiba power transistors, I do not get a relay click in the protection circuit. If I unplug them, the click of the relay does happen. It also appears that the spot is still getting warm on the board in the same spot. I do have it hooked to a dim bumb tester, so it may be preventing it from cooking as hot as it did before.
Any ideas from the expert? At this stage, I'm just a parts replacer and still trying to wrap my head around reading circuits and diagnosing them at that level. The only service manuals I could find are also barely legible, when it comes to the voltage values on components, so that doesn't help either...
I've attached a photo of the problem area. Sorry for the wall of text and thanks!
