• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

SA-8100 protection circuit issue

Use the 512-KSA992FBU. Order more than you'll need, if you order 10 or more you get a small discount on price. Also, to confirm, did you measure the offset at the speaker terminals or did you measure it at the power amp board when in protection? When in protection you need to measure the offset at pin 3 for the left channel and pin 23 for the right.
 
Thanks for clarifying on the transistor.

I only measured at the speaker, which I realize is probably not a good measurement. I can measure it on the power amp board and see what I get. Problem is it only goes into protection mode for 2 or 3 seconds, so not sure how good of a reading I can really get.
 
OK, was able to measure voltages at pins 3 and 23 on the power amp board. Both pins settled down after initial powerup. Pin 3 was steady at -1.5 mV and went to zero when the protection circuit tripped. Pine 23 was steady at just under -1 mV and also went to zero when the protection circuit tripped.

Will be ordering the transistors tonight unless someone tells me these readings indicate something else.

Thanks,
Keith
 
Don't order yet, we're not quite done. Which board number is the protection board? The board in question is the one directly under the power amp board, you will need to take off the bottom cover to see it. The board number will be AWM-027 with a suffix, I need to know which suffix it is, as they have very different parts depending on the suffix. I'm beginning to suspect Q1 and Q2 on that board are becoming flaky.
 
You have the early model board. That board could stand to be recapped and have new transistors put in. Here is my list for that board (with credit to markthefixer), simple and cheap and adds the flyback diode for the relay coil.

AWM-027-D (A revision has 2SC857 transistors in Q1 and Q2 positions, also .056uF mylar caps in C1 and C2 positions, use the D version parts and replace them.)

AWM-027-D: C1: .22uF 10v CSSA: 80-F612JF224J063A .22uF 63v
AWM-027-D: C2: .22uF 10v CSSA: 80-F612JF224J063A .22uF 63v
AWM-027-D: C3: 330uF 6.3v CEA: 647-UPW1E331MPD 330uF 25v
AWM-027-D: C4: 330uF 6.3v CEA: 647-UPW1E331MPD 330uF 25v
AWM-027-D: C5: 4.7uF 25v CEA: 647-UPW1V4R7MDD 4.7uF 35v
AWM-027-D: C6: 100uF 16v CEA: 647-UPW1E101MED 100uF 25v

Q1: 2SC869: 512-KSC1845FTA
Q2: 2SC869: 512-KSC1845FTA
Q6: 2SC945: 512-KSC2383YTA
Q7: 2SC1384: 512-KSC2690AYS (need to enlarge board holes for replacement)

512-1N4004 to pins 14 (Unbanded end, anode) and 15 (banded end, cathode)

BOM List (for Mouser)

80-F612JF224J063A | 2
647-UPW1E331MPD | 2
647-UPW1V4R7MDD | 1
647-UPW1E101MED | 1
512-KSC1845FTA | 2
512-KSC2383YTA | 1
512-KSC2690AYS | 1
512-1N4004 | 1

Also, since you'll be replacing the 2SA726 transistors on the power amp replace the two 2SC1451 transistors as well, they are just as troublesome if not more so. Replacement is 512-KSC3503DSTU. You will need to enlarge the board holes slightly for the 3503s as well. Remember that the replacements are of a different lead configuration than the originals! Pay attention to how you put the replacements in. If you need help with this please ask, no such thing as a stupid question here.
 
OK, thanks Matt, I will put an order together for those parts. This is looking like quite the project, but worth it. This amp sounds great, so anything I can do to make it better and extend the life will be good. I will definitely need direction if any of the parts are to be installed different from what is in there. My standard assumption is they should go in the same way, but please list any parts that do not and how they should be installed. I assume capacitors can be installed either way with only two contacts, but I know the three contacts on transistors need to go in one configuration.

On another note, I did solve the Phono 1 hum problem. It was indeed an open ground on the L channel. Was able to solder that connection to correct the problem.

Thanks for all the assistance,
Keith
 
caps go in the same, roughly

but transistors.... that's a BIG NO-NO!!!!!!! It was too much to ask for the industry to make the replacements with the same pin layouts as the originals. (that's sarcasm)
So the replacements ARE different from the originals in a LOT but not ALL cases.

So, you got some learnin to do. Once learned it will stay with you. there are plenty of explanations and examples in threads on this forum.

you need to identify the pin layouts using the DATASHEETS of the replacement transistors.
 
Thanks Mark, I will be extra careful with the transistors. I'll be asking questions here if I have any doubt. The 8100 circuit diagrams have every transistor labeled. I assume the line with the arrow to the plate is the direction of the signal. Some arrows point toward the plate and in other cases it points away. I also assume the lines on the same side of the plate are the signal (one signal in and the other signal out) while the line on the other side of the plate is power. Is that generally correct? Assuming the new transistors have a similar diagram, I will be able to follow that. Oh, my, that's a lot of assumptions!

On another note, I thought some of the caps on the protection board had leaked because I saw what looked like amber colored goo around the base of the capacitor on the circuit board. However, I was talking with a friend who fixes old stereo equipment and he said that the larger caps were glued to the board and that what I was seeing was probably glue and not a leaky cap. Does that sound right?
 
PNP and .NPN
ae430c.gif

http://www.physlink.com/education/askexperts/ae430.cfm
 
Thanks Pete, just did a bunch of reading on transistors to educate myself and saw that the arrows indicate the two types of transistors. Still learning! So, on diagrams is it the case that the line with the arrow is always the emitter and base is always on the other side of the plate?

Thanks!
 
Parts should come in today. I do have several questions.

1. Q1 and Q2 on the revision A protection board are 2SC857K-A, but Matt listed them as 2SC869, which I assume is what is on the revision D board. The replacement I ordered is 512-KSC1845FTA. Is this the correct replacement for 2SC857K?

2. What is the purpose for adding the 1N4004 resistor between pins 14 and 15? I assume it is because the replacement transistor (Q7) is not an exact replacement for 2SC1384?

3. I thought some of the caps were leaking, but that does not appear to be the case. My thought was to replace the resistors and leave the caps alone at this point and see if replacing the transistors solves the protection issue. Would there be any problems with this approach?

Thanks!
 
1= c1845 is correct

2=
1n4004 diode short circuits a horrendous voltage pulse delivered BY the relay coil when the current is shut off.
All that magnetic field (1 watt's worth) collapses and the moving lines of magnetic force induce that energy BACK INTO the relay coil.
Until current flowed, the voltage would build across the coil until something gave out and current flowed. Usually the relay driver transistor "leaked".
By allowing the voltage to rise to only 0.6v before current flows, that high voltage does NOT blast in breakdown across the driver transistor.

3=
Cart before horse. Caps more likely to failure than resistors. E-Caps DO dry out and corrode internally. They are on a life timer.
 
Thanks for that info Mark. A couple of members pointed out the transistors as the likely problem, so that is why I was thinking about replacing those first. It would be interesting to determine if the resistors or capacitors are causing the issue. I will likely work on the amp tomorrow. Hope all goes well!
 
Installed the 726 replacements on the power amp board and the Q1 & Q2 replacements on the protection board. Thought I would check to see if all was working, so turned the amp on. The amp does not come out of protection. :( Have I done something wrong and this point, or is this expected?
 
I used the transistor data sheets to determine emitter, collector, and base. The transistor direction is marked on the board, so I followed that when placing each transistor in.
 
You must log in or register to reply here.
Back
Top Bottom