Well I am done with the protection board. There are a few things it didn't fix and a few lessons I've learned.
The replacement of the protection relay was not necessary as recommended. After I replaced it, I opened the old one. Not one sign of corrosion, pitting, burning, etc. It was pristine and looked new. I've kept it as a spare and a reminder. The soft start I did not replace as the part number noted from mouser gets you a relay with different connection points as well as spade connectors instead of pins. I double checked the part number to what arrived and it is correct. Anyone wanting to replace their soft start might want to double check before ordering. Also, since I couldn't replace it, I worked on opening it while installed. It, too, was pristine inside and was not in need of replacement.
I replaced all caps and made one mistake of using a higher value because I didn't bother double checking and it turns out a higher value was in among the lower ones. This had the effect of delaying startup to 51 seconds. Once I realized my mistake, and fixed it, start up was down to 5 seconds.
The issue of the stereo indicator light flashing when the soft start relay disengages on power down didn't go away. Looking over the schematics, it appears the indicator is connected to a 13V constant source and it triggered when pin 8 on the PA1001A is grounds the other lead to the indicator. The SM doesn't give any indication as to what causes pin 8 to ground, so I'm at a loss. The only thing I can do is recap the tuner's electrolytic caps and hope that's the issue. I refrained from doing a recap years ago because so many told me that doing so could knock the tuner out of alignment and would need realigning with specialized equipment. So I left it. Of course, now that I listen to the FM on this unit, I notice quite a bit of distortion on the high end. The mid and lows sound fine, but the upper end is distracting. I'm hoping a recap will fix both.
While I was in there, I did the center voltage and idle current. I managed to get the center voltage on each down to .01 and the idle dead on 30V (after letting it sit powered on for 30 minutes each channel before adjusting). Also did the power meters with a CD playing 1kHz sine wave test tone and adjusting volume until I hit 31V on the speaker outputs. Once there, I adjusted the pots for the meters until they both read 0db.
Fun stuff!
If you've read this far, then you might just be the one to answer the following question:
Are the Nichicon KW, KG or KX a suitable replacement for the low leakage orange electrolytic caps, especially as found on the tuner board (10 of them, if I recall correctly).
Thanks!
The replacement of the protection relay was not necessary as recommended. After I replaced it, I opened the old one. Not one sign of corrosion, pitting, burning, etc. It was pristine and looked new. I've kept it as a spare and a reminder. The soft start I did not replace as the part number noted from mouser gets you a relay with different connection points as well as spade connectors instead of pins. I double checked the part number to what arrived and it is correct. Anyone wanting to replace their soft start might want to double check before ordering. Also, since I couldn't replace it, I worked on opening it while installed. It, too, was pristine inside and was not in need of replacement.
I replaced all caps and made one mistake of using a higher value because I didn't bother double checking and it turns out a higher value was in among the lower ones. This had the effect of delaying startup to 51 seconds. Once I realized my mistake, and fixed it, start up was down to 5 seconds.
The issue of the stereo indicator light flashing when the soft start relay disengages on power down didn't go away. Looking over the schematics, it appears the indicator is connected to a 13V constant source and it triggered when pin 8 on the PA1001A is grounds the other lead to the indicator. The SM doesn't give any indication as to what causes pin 8 to ground, so I'm at a loss. The only thing I can do is recap the tuner's electrolytic caps and hope that's the issue. I refrained from doing a recap years ago because so many told me that doing so could knock the tuner out of alignment and would need realigning with specialized equipment. So I left it. Of course, now that I listen to the FM on this unit, I notice quite a bit of distortion on the high end. The mid and lows sound fine, but the upper end is distracting. I'm hoping a recap will fix both.
While I was in there, I did the center voltage and idle current. I managed to get the center voltage on each down to .01 and the idle dead on 30V (after letting it sit powered on for 30 minutes each channel before adjusting). Also did the power meters with a CD playing 1kHz sine wave test tone and adjusting volume until I hit 31V on the speaker outputs. Once there, I adjusted the pots for the meters until they both read 0db.
Fun stuff!
If you've read this far, then you might just be the one to answer the following question:
Are the Nichicon KW, KG or KX a suitable replacement for the low leakage orange electrolytic caps, especially as found on the tuner board (10 of them, if I recall correctly).
Thanks!
