distortion13
New Member
I recently finished re-capping a portion of my SX-1280 receiver, including the replacement of other components, in an effort to increase the life cycle and performance of this receiver. Before moving on to re-capping the main caps and those in the power amps, I fired it up to check things out. Upon power up the relay on the protection board keeps cycling on and off with approx. 3 seconds between changes in state (on vs. off vs. on again, etc.). This receiver was working before the re-capping efforts. Any help would be, as always, greatly appreciated.
After reading a post on a similar issue, I started to adjust the DC balance of the power amplifiers per the manual. With VR2 fully clockwise and VR1 centered, per chapter 10.3, I get readings at pin 14 of each amp board way out of the acceptable limits as follows. As I understand it, these figures should be 0V +/- 20mV.
Left Channel: 4.51V Pin 14 to Grd.
Right Channel: 4.75V Pin 14 to Grd.
The boards re-capped to this point are as follows.
AWE-092 Tuner
AWF-031 EQ Amp
AWG-060 Flat Amp
AWG-059 Tone Amp
AWM-119 Filter Amp
AWM-123 Protection Board
AWR-157 Power Supply
The electrolytic cap replacement is pretty straight forward, but I am including a list of the transistors (and Misc) changed on the power supply and protection boards below in the event that I may have crossed something incorrectly.
AWR-157 Power Supply (Q6 and Q7 are especially concerning)
Q1 - 2SD712 D or C part used is Mouser 512-KSC2073TU (Replaced heat sink compound as well)
Q2 - 2SB682 D or C part used is Mouser 512-KSA940TU (Replaced heat sink compound as well)
Q3 - Component tested and re-used - didn't have a replacement at the time.
Q4 - 2SA904A-G or F part used is Mouser 512-KSA1013YBU
Q5 - 2SB682 D or C part used is Mouser 512-KSA940TU (Replaced heat sink compound as well)
Q6 - 2SC945A-Q or R part used is Mouser 512-KSC945CYTA
Q7 - 2SC945A-Q or R part used is Mouser 512-KSC945CYTA
D1-D4, D11-D12 - Radio Shack 1N4004 used.
AWM-123 Protection Board
Caps only. Q1 and Q2 were left alone.
After reading a post on a similar issue, I started to adjust the DC balance of the power amplifiers per the manual. With VR2 fully clockwise and VR1 centered, per chapter 10.3, I get readings at pin 14 of each amp board way out of the acceptable limits as follows. As I understand it, these figures should be 0V +/- 20mV.
Left Channel: 4.51V Pin 14 to Grd.
Right Channel: 4.75V Pin 14 to Grd.
The boards re-capped to this point are as follows.
AWE-092 Tuner
AWF-031 EQ Amp
AWG-060 Flat Amp
AWG-059 Tone Amp
AWM-119 Filter Amp
AWM-123 Protection Board
AWR-157 Power Supply
The electrolytic cap replacement is pretty straight forward, but I am including a list of the transistors (and Misc) changed on the power supply and protection boards below in the event that I may have crossed something incorrectly.
AWR-157 Power Supply (Q6 and Q7 are especially concerning)
Q1 - 2SD712 D or C part used is Mouser 512-KSC2073TU (Replaced heat sink compound as well)
Q2 - 2SB682 D or C part used is Mouser 512-KSA940TU (Replaced heat sink compound as well)
Q3 - Component tested and re-used - didn't have a replacement at the time.
Q4 - 2SA904A-G or F part used is Mouser 512-KSA1013YBU
Q5 - 2SB682 D or C part used is Mouser 512-KSA940TU (Replaced heat sink compound as well)
Q6 - 2SC945A-Q or R part used is Mouser 512-KSC945CYTA
Q7 - 2SC945A-Q or R part used is Mouser 512-KSC945CYTA
D1-D4, D11-D12 - Radio Shack 1N4004 used.
AWM-123 Protection Board
Caps only. Q1 and Q2 were left alone.