Hi,
I'm currently trying to reapair a Technics SU-300 Amp. The Main Fuse F1 (at the primary side of the transformer) blows when the main power button is switched. I already found at that the transformer is ok by disconnecting the transformer from the pcb with the rectifier diodes (D601 to 604) (--> fuse didn't blow). I also measured the resistence of the diodes in both directions while they were still soldered in but surprisingly all of them showed a resistance of several kOhm in both directions. Any advice on this? Should I dissolder them and try again?
I also measured the resistance of the capacitors C130 and C131. It was in the MOhm range, so I guess these should be okay.
Here you can find the schematic (German / EG-Version:
http://www.vintageshifi.com/repertoire-pdf/pdf/telecharge.php?pdf=Technics-SU-300-Service-Manual.pdf
Thank you!
I'm currently trying to reapair a Technics SU-300 Amp. The Main Fuse F1 (at the primary side of the transformer) blows when the main power button is switched. I already found at that the transformer is ok by disconnecting the transformer from the pcb with the rectifier diodes (D601 to 604) (--> fuse didn't blow). I also measured the resistence of the diodes in both directions while they were still soldered in but surprisingly all of them showed a resistance of several kOhm in both directions. Any advice on this? Should I dissolder them and try again?
I also measured the resistance of the capacitors C130 and C131. It was in the MOhm range, so I guess these should be okay.
Here you can find the schematic (German / EG-Version:
http://www.vintageshifi.com/repertoire-pdf/pdf/telecharge.php?pdf=Technics-SU-300-Service-Manual.pdf
Thank you!
Use a bulb tester. This will save damage and fuse blowing.
Large diodes usually fail short circuit and so at this stage I would accept that they are probably OK. Any slight residual voltage (charge on caps) will totally confuse most DVM's when checking resistance, that said a short will always show.
Most likely failure is the power output chip. This is easily proved by unsoldering the supplies to it and then seeing if the amp powers up.
Large diodes usually fail short circuit and so at this stage I would accept that they are probably OK. Any slight residual voltage (charge on caps) will totally confuse most DVM's when checking resistance, that said a short will always show.
Most likely failure is the power output chip. This is easily proved by unsoldering the supplies to it and then seeing if the amp powers up.
Thanks for your answer. By "power output chip" you mean the SVIK4141-2M (as in the manual)? I think in reality it's STKxxx since I couldn't find anything else. I found these two versions, the power pins are 9 and 11, right? I will check this today and see if this is the problem.
STK4141II
https://www.reichelt.de/index.html?ACTION=7&LA=3&OPEN=0&INDEX=0&FILENAME=A200%2FSTK41xxII%23SAN.pdf
STK4141V
http://cdn-reichelt.de/documents/datenblatt/A200/stk4141v_sanyo.pdf
Pins 9 and 11
STK4141II
https://www.reichelt.de/index.html?ACTION=7&LA=3&OPEN=0&INDEX=0&FILENAME=A200%2FSTK41xxII%23SAN.pdf
STK4141V
http://cdn-reichelt.de/documents/datenblatt/A200/stk4141v_sanyo.pdf
Pins 9 and 11
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