Thanks inductor for sharing your experience with us. The TO-126 running cold sounds good, at 8 watt power rating I imagine it would be. I have noted the 2sc1451 had a EBC lead arangement and the KSC2682 has a ECB. Inductor, do you think the KSC2682 would do the job? The 2sc2911's are more difficult for me to come by for some reason. Also, how about the NTE287? It has 300V 500ma 1.5w rating. I'm concerned however that the gain is low as is the 50mhz frequency. However it does use the same EBC lead arangement. If everybody agrees, I think the KSC2682's with the TO-126 case might be the easiest to buy in small quanities. Thanks again guys, we are making progress.
Sa-9100, DC offset question, Protection light
- Thread starter mpgasque
- Start date
NTE is just about the LAST choice in transistors, they are remarked whatevers that NTE bubble packs and remarkets at a tremendous markup. You (and sometimes they) never know what you're getting.
That's why I go with On-Semi's and Fairchild.... a name and domestic...
plus most are available at mouser and digikey.
Counterfeit transistors are common... so you want to go with a reliable distributor.
Lead arrangements are no problem, here's something I posted a long time ago that should give the general idea:
That's why I go with On-Semi's and Fairchild.... a name and domestic...
plus most are available at mouser and digikey.
Counterfeit transistors are common... so you want to go with a reliable distributor.
Lead arrangements are no problem, here's something I posted a long time ago that should give the general idea:
Thanks Mark, I did note that the prices of the NTE transistors were really high in relation to some other makers. But the most serious problem would be to not know what your getting. The diagram is great, thanks for posting it.
The "Time to Failure" seems to vary, perhaps due to the volume level I'm listening to. At low volume I've gone an hour without failure and then I just turned the system off. At higher volume. the protection will popup after as little as 10 min. I'm keeping track of this so not to be fooled that it's fixed. Thanks everyone for your posts.
The "Time to Failure" seems to vary, perhaps due to the volume level I'm listening to. At low volume I've gone an hour without failure and then I just turned the system off. At higher volume. the protection will popup after as little as 10 min. I'm keeping track of this so not to be fooled that it's fixed. Thanks everyone for your posts.
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I would rather hit my head with a hammer..... HARD......
This transistor has already PROVED it's long term unreliability......
(it's not the first to do THAT though...)
Volume related, huh?
I reread the thread, I saw no mention of deoxiting...
Ok, I thought I'd mention my Hong Kong source for the originals. I assume from this that the sound will be pretty much unchanged using the 2sc2682's. I'm kinda glad everybody said deep six the fujis since it was a lot of money anyway, a real lot of money. I'll go ahead and order the 2sc2682's in the morning.
I'm not sure that the problem is volume related. As I already posted, the amp has popped into protection with no speakers attached and zero volume when I was testing the DC offset and the bias. I have cleaned up many of the pots and switches with my Detoxit 5% spray. Sometimes the right channel would drop out until I would tap the volume knob. Then it would usually come back to life. I knew the pot probably needed cleaning, so after hitting the pots with the detox it cleared up and I've had no problems with the volume since. Thanks once again.
I'm not sure that the problem is volume related. As I already posted, the amp has popped into protection with no speakers attached and zero volume when I was testing the DC offset and the bias. I have cleaned up many of the pots and switches with my Detoxit 5% spray. Sometimes the right channel would drop out until I would tap the volume knob. Then it would usually come back to life. I knew the pot probably needed cleaning, so after hitting the pots with the detox it cleared up and I've had no problems with the volume since. Thanks once again.
Well, the parts (512-KSC2682YSTU) came in and I have enough to replace Q6 & Q7 on the power amp board, AWH-023, on both the right and left channel (2Q6's & 2Q7's). Yes, the bias will have to be reset and the DC offset will be checked also. The original had a EBC lead arangement and the 2682's have a ECB arangement.
Sometimes this amp goes for an hour without the protection cutting in. Like Mark said, ummm.....
Sometimes this amp goes for an hour without the protection cutting in. Like Mark said, ummm.....
When powering up, just to be safe, use a dim-bulb tester. Basically it is an incandescent light bulb (40w? 60w?) that goes in series with the ac line, like a fuse or power switch and if there is a short, or a bias problem that turns the output transistors on HARD, it will limit the amount of current available to do damage.
It will initially glow brightly for a few seconds then dim out as the capacitors are charged, if things are working right. If not, it will STAY bright.
Start out with your bias resistor adjustment at ZERO ohms ("VR3 all the way clockwise"), that will be the MINIMUM bias.
It will initially glow brightly for a few seconds then dim out as the capacitors are charged, if things are working right. If not, it will STAY bright.
Start out with your bias resistor adjustment at ZERO ohms ("VR3 all the way clockwise"), that will be the MINIMUM bias.
Mark, you say to start off with min bias, turn VR3 all the way clockwise, however the Service manual says to adjust the bias, start out by turing VR3 all the way COUNTERCLOCKWISE (looking down at VR3). Do I have to test the variable resistor to find out which way gives me zero ohms?
Well, the service manual wouldn't have you turn the bias all the way up (too dangerous) so go with the manual, the ohms test was recommended as an ultimate test in case the service manual OR I was wrong, both sometimes happen.
I never trust the manual or myself in that case, thus the ohmmeter test.
And I see I blew it, IN A QUOTE, no less.....:sigh:
Good catch!!
My dislexia has taken a new turn........ I just used to swap numbers... so I'm more careful with the numbers....
I never trust the manual or myself in that case, thus the ohmmeter test.
And I see I blew it, IN A QUOTE, no less.....:sigh:
Good catch!!
My dislexia has taken a new turn........ I just used to swap numbers... so I'm more careful with the numbers....
Thanks for the quick reply. I did the meter test and turning the pot (VR2) clockwise did drop the ohms. This is a 100 ohm pot. Both channels are about 60 ohms. Should I bring them all the way down or about 20 ohms? Thanks. Remember, there is already one typo on that SM page. What makes sense?
zero ohms is the safest. then adjust upward to spec, watch it in case it climbs (if it climbs, then turn it down to spec) after 20 minutes it should stabilize.
this is because you are starting out with new transistors in the bias section, thus the old conditions and setting will probably be wayyyyy off.
this is because you are starting out with new transistors in the bias section, thus the old conditions and setting will probably be wayyyyy off.
Sounds good. It did climb when I did the initial bias reading with the old stuff. Started out at 15V and after 20 minutes got up to about 23V. Both channels did the same thing. I'm powering this thing up on my patio outside, just in case it becomes a campfire. Will be back in touch.
Well, I put the marshmellows away since everything was well behaved upon power up. Just a note for anyone reading this in the future, the SA-9100 service manual, section 9 refers to VR2 incorrectly as VR3 in the text, but the picture is correct. They also correctly say to rotate VR2 all the way counterclockwise when beginning to adjust the bias. I did mine the other way (clockwise) but I had the meter on it when I switched the power on. The bias reading shot up to 175mv and I turned it down on both channels right away. Didn't seem to bother anything.
Keep in mind that unless you have rebuilt sections of the bias circuit, all you need to do is to measure your present bias value and just tweak VR2 a TINY amount (factory spec is 25mv). I set mine (after 20 min) at 24mv on both channels. Keep in mind they will start around 15mv and climb to the final value. In 20 min the channels should quit the climb and stabilize.
The DC offset was set at 1.0mv on both channels also.
The work went well with no major problems, but it was more difficult than the other work I had preformed. Great attention must be paid to EBC vs ECB.
Now to crank the music up and see if the problem is still with me. Thanks for everyones help.
Keep in mind that unless you have rebuilt sections of the bias circuit, all you need to do is to measure your present bias value and just tweak VR2 a TINY amount (factory spec is 25mv). I set mine (after 20 min) at 24mv on both channels. Keep in mind they will start around 15mv and climb to the final value. In 20 min the channels should quit the climb and stabilize.
The DC offset was set at 1.0mv on both channels also.
The work went well with no major problems, but it was more difficult than the other work I had preformed. Great attention must be paid to EBC vs ECB.
Now to crank the music up and see if the problem is still with me. Thanks for everyones help.
I've got my fingers crossed.....
(toes too...)
(toes too...)
Well I'm sorry to say that the problem is still with me. After running for 30 min with no problem the first time, and 18 min the second time, the protection kicked in the third time after 16 min. The fourth time I went a full hour with no problem before I turned off the music. On the bright side, the amp plays great and the music sounds as good as ever. So my workmanship was good and the choice of the c2682's to replace the c1451's was also good.
What makes this difficult is the very long time between "events". The time it kicked out when I was measuring the bias might have been caused by my taking the measurments (the Hizenburg Principal?). Pins 9 and 13 are where the readings are taken and they also feed in to the protection circuit.
Since the time between failures is great and the event is very short, I can either live with it, or shotgun it. The parts are cheap so I think I'll pump up the 12 gage. I think the problem is with a semiconductor, not a capacitor, resistor, or other passive element. I don't think it's a cold solder joint or a diode either. The part fails for an instant, then comes back to life.
First I'll replace the 8 transistors on the power supply board, AWR-032. Having already recapped it, this should not be a problem, it's easy to work on. Then I'll assume that, if the readings are ok, the board is stable.
If no success, I'll replace the remaining 6 transistors on the protection board (AWM-025). It's also easy to work on. Once again, with almost all new components, I'll assume the board is good.
If the problem is still with me, I'll assume that the problem must be in one of the power amps (AWH-023). At this point I'll stop and ponder what to do next. Your thoughts are always welcome.
What makes this difficult is the very long time between "events". The time it kicked out when I was measuring the bias might have been caused by my taking the measurments (the Hizenburg Principal?). Pins 9 and 13 are where the readings are taken and they also feed in to the protection circuit.
Since the time between failures is great and the event is very short, I can either live with it, or shotgun it. The parts are cheap so I think I'll pump up the 12 gage. I think the problem is with a semiconductor, not a capacitor, resistor, or other passive element. I don't think it's a cold solder joint or a diode either. The part fails for an instant, then comes back to life.
First I'll replace the 8 transistors on the power supply board, AWR-032. Having already recapped it, this should not be a problem, it's easy to work on. Then I'll assume that, if the readings are ok, the board is stable.
If no success, I'll replace the remaining 6 transistors on the protection board (AWM-025). It's also easy to work on. Once again, with almost all new components, I'll assume the board is good.
If the problem is still with me, I'll assume that the problem must be in one of the power amps (AWH-023). At this point I'll stop and ponder what to do next. Your thoughts are always welcome.
Ok, we tried the Hail Mary play, and it didn't work.
Now we start honest troubleshooting....
I could get behind the power supply upgrades, but you will be waiting for parts anyway, so you might as well try this. If it still does it without the amp outputs connected to the protection circuits, then the protection circuits and the power supply are suspect.
Just to be sure, so far the protection board has gotten caps and the amp boards got two transistors each, right?
The power supply was recapped? And was that nte Q7 protection relay driver transistor installed?
If not, you might want to try installing a new Q7 first.
Now we start honest troubleshooting....
I could get behind the power supply upgrades, but you will be waiting for parts anyway, so you might as well try this. If it still does it without the amp outputs connected to the protection circuits, then the protection circuits and the power supply are suspect.
Just to be sure, so far the protection board has gotten caps and the amp boards got two transistors each, right?
The power supply was recapped? And was that nte Q7 protection relay driver transistor installed?
If not, you might want to try installing a new Q7 first.
Power supply:
q1 bce 2sd313 / bce ksd526
q2 bce 2sb507 / bce ksb596
q3 ecb 2sc945 / eBC ztx694b / ebc ksc945
q4 ecb 2sa720 / eBC ztx795a /
q5, q7 ecb 2sc1318 / eBC ztx694b
q6, q8 ecb 2sa720 / eBC ztx795b oops...a / a bit late at night & not sleeping well with the heat...
The ztx are a bit pricey at a little over a buck each, but they are superior transistors that have the current capability, gain and power dissipation to spare. (voltage too)
protection:
q1, q2 ebc 2sc857 / ecb ksc1845
q3, q4, q6 ecb 2sc945 / ebc ksc945
q5 ecb 2sa733 / ebc ksa733
q7 ecb 2sc1384 / ebc ztx694b
just my $0.02 worth....
q1 bce 2sd313 / bce ksd526
q2 bce 2sb507 / bce ksb596
q3 ecb 2sc945 / eBC ztx694b / ebc ksc945
q4 ecb 2sa720 / eBC ztx795a /
q5, q7 ecb 2sc1318 / eBC ztx694b
q6, q8 ecb 2sa720 / eBC ztx795b oops...a / a bit late at night & not sleeping well with the heat...
The ztx are a bit pricey at a little over a buck each, but they are superior transistors that have the current capability, gain and power dissipation to spare. (voltage too)
protection:
q1, q2 ebc 2sc857 / ecb ksc1845
q3, q4, q6 ecb 2sc945 / ebc ksc945
q5 ecb 2sa733 / ebc ksa733
q7 ecb 2sc1384 / ebc ztx694b
just my $0.02 worth....
Just to recap what has been done (no pun intended) the protection board has new caps and a new NTE293 for Q7 installed along with the 1N4004 diode. The power supply board (AWR-032) has new caps. The power amp board (AWH-023) has, on both channels, replacements for the 2 c1451's, the c2682Y's.
This amp does this when I'm listening with headphones, with the speakers turned off. I don't have any cheap speakers, I'll look around. how about monitoring with headphones, not wearing them but laid on a table close by? Also, without the protection circuit, could the failure damage other components? I studied the relay on the schematic and saw one channel being grounded (?), the other channel floats. As mark said, What?
Thanks for the part numbers. NTE has a matched pair of NPN, PNP at Mouser, 526-NTE290AMCP. Would a matched pair be best? This is for the power supply board (AWR-032) Q5 & Q6 pair, and Q7 & Q8 pair. Thanks.
This amp does this when I'm listening with headphones, with the speakers turned off. I don't have any cheap speakers, I'll look around. how about monitoring with headphones, not wearing them but laid on a table close by? Also, without the protection circuit, could the failure damage other components? I studied the relay on the schematic and saw one channel being grounded (?), the other channel floats. As mark said, What?
Thanks for the part numbers. NTE has a matched pair of NPN, PNP at Mouser, 526-NTE290AMCP. Would a matched pair be best? This is for the power supply board (AWR-032) Q5 & Q6 pair, and Q7 & Q8 pair. Thanks.