SA-8500 Issue

x2turbo

Well-Known Member
A friend gave me a SA-8500 that is having issues and hoping for some advice.

It powers up and comes out of protection and actually sounds good for the first few seconds and then degrades into distortion and the sound level fades.

I tried following the procedures in the service manual to set the junction point and idle current but it's not working very well.

I turned VR1 and VR2 clockwise to 0 but turning the VR3 or VR4 has no real effect. Starts out at -175mv and can get it to move to -165mv with a full spin of the pot.

By adjusting both VR1 and VR3 I was able to eventually get the values where they should be but it didn't have any positive effect on the sound.

I'd like to get it working again without taking a shotgun approach as that hasn't always fared well for me in the past. Live and learn.

Thanks
 
Shotgun approach is what you will have to do. The amp (not just the power amp section) is loaded with 2sa726 and 2sc1451 troublemakers as well as the dreaded sky blue sanyo caps.
 
I went thru the list, sorry it was a stupid question to ask.

One part no longer available.
Q5: 2SC1451: 512-KSC3503ESTU

Is this a suitable replacement ? 512-KSC3503DSTU
 
I just fixed my posts in that thread, but the list isn't complete, missing protection circuit, power supply etc.

all you NEED to do is the cssa caps, and the aforementioned transistors.

but to the point, all transistor numbers are current, you MIGHT catch me on some gain or packaging (bulk / tape etc) gobbletygook on the ending letters in each number, but the transistor types are current.


edit - you beat me by seconds - I was going to check.... I shouldn't have taken time to do the "gobbletygook" line... lol...

yes dstu is fine slight gain reduction from estu to dstu. been using dstu's with no problem, it's an old thread.
 
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I'm curious too. My SA-7500 has the same issue, probably for the same reasons. I'm working on a list. So please keep us posted on your findings.
 
The parts are arriving today. Is there a recommendation as to the order of the boards I replace them in to help pinpoint the issue for others having the same problem?
 
Get the power amplifier board working first. With the known troublemakers.

Then we have a good point to check from as the other boards are done.

second would be protection, we're not doing it first because we are NOT going to use speakers yet, and the we KNOW the power amp is bad.

third would be power supply

This is specific for YOUR unit, normally it would be power supply, protection and then the power amp.

Thing is, we never explicitly checked your power supply voltages. Quite frankly, there were too many assumptions on my part.
 
I replaced the following parts

Power Amp Assembly (AWH-042-0)

AWH-042-0: C1: .47uF 25v CSSA: 667-ECQ-V1H474JL .47uF 50v
AWH-042-0: C2: .47uF 25v CSSA: 667-ECQ-V1H474JL .47uF 50v
AWH-042-0: C3: 33uF 16v CEA: 647-UPW1C330MDD 33uF 16v
AWH-042-0: C4: 33uF 16v CEA: 647-UPW1C330MDD 33uF 16v
AWH-042-0: C9: 220uF 6.8v CEA: 647-UPW1A221MED 220uF 10v
AWH-042-0: C10: 220uF 6.8v CEA: 647-UPW1A221MED 220uF 10v
AWH-042-0: C11: 47uF 50v CEA: 647-UPW1H470MED 47uF 50v
AWH-042-0: C12: 47uF 50v CEA: 647-UPW1H470MED 47uF 50v

Q1: 2SA726: 512-KSA992FBU
Q2: 2SA726: 512-KSA992FBU
Q3: 2SA726: 512-KSA992FBU
Q4: 2SA726: 512-KSA992FBU
Q5: 2SC1451: 512-KSC3503DSTU
Q6: 2SC1451: 512-KSC3503DSTU

Waiting for any instructions before I move forward

Thanks
 
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Sometimes this hobby can be so frustrating.

I powered it up this morning just to make sure it came out of protection. I did not :no:

I checked connectivity for all my solder joints and there are good. Only thing I can figure is maybe I positioned the transistors wrong.

I looked both the ksa992 and ksc3503 and found both were ecb. Based on the service manual that meant flipping the ksa992s 180 degrees and swapping the bc on the ksc3503s.

Did I miss something?

Edit: I reverified the pins on the ksa992 against the silkscreen instead of the schematic. I had the ec reversed. It comes out of protection now. :banana:
 
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Doing some general reconnaissance around the amp section. It's definitely been worked on before. Output resistors on left channel are original, right have been replaced by ecg130 and ecg219.

I did not order new output transistors. Should I have? Also I did not get driver replacements. 863-MJE15028G and MJE15029G suitable replacements?
 
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drivers: 2sa814, 2sc1624 120v 1a 15w 70-240 30mhz ()

from my notes:
863-MJE15029G pnp to-220 bce 120v 8a 50w 30mhz 70hfe $1.30 watch the Vbe turnon!!
863-MJE15028G npn to-220 bce 120v 8a 50w 30mhz 70hfe $1.30


That means in situations where voltage drops are critical, On-Semi's slightly reduced turn on voltage (which is usually good) can result in idle currents that might be too high even with the variable resistor at zero ohms.

512-KSA940TU pnp to-220 bce 150v 1.5a 25w 4mhz 40-140hfe $0.62
512-KSC2073TU npn to-220 bce 150v 1.5a 25w 4mhz 40-140hfe $0.66
will do fine, the drivers are neutralized by base to collector capacitors so their frequency spec isn't critical.
 
Thanks Mark

Since I have to order more parts I'm going to order the following to hopefully complete the full recap. I'm building on the BOM from the thread referenced above. Also if any of these parts are best left alone unless a known issue it would be good to know and lastly are there any zeners that should be replaced.

Thanks for the help.

Equalizer Amplifier Assembly (AWF-016-A)
Q3 2SC1313 KSC1845PBU (have these on hand, any important difference from EBU?)
Q4 2SC1313 KSC1845PBU
Q5 2SC1313 KSC1845PBU
Q6 2SC1313 KSC1845PBU

Control Amplifier Assembly (AWG-034-A)
Q3 2SC1312 KSC1845PBU
Q4 2SC1312 KSC1845PBU
Q5 2SC1312 KSC1845PBU
Q6 2SC1312 KSC1845PBU
Q7 2SC1312 KSC1845PBU
Q8 2SC1312 KSC1845PBU

Power Amplifier Assembly (AWH-042-0)
Output Transistor 2SD371 863-MJ21194G
Output Transistor 2SD371 863-MJ21194G
Output Transistor 2SB531 863-MJ21193G
Output Transistor 2SB531 863-MJ21193G
Output Transistor 2SD371 863-MJ21194G
Output Transistor 2SD371 863-MJ21194G
Output Transistor 2SB531 863-MJ21193G
Output Transistor 2SB531 863-MJ21193G
Q7 2SC1624 863-512-KSC2073TU
Q8 2SC1624 863-512-KSC2073TU
Q9 2SA814 512-KSA940TU
Q10 2SA814 512-KSA940TU

Switch Circuit Assembly (AWS-83-D)
Q1 2SC1626 ????????
Q2 2SC945 512-KSC1845FTA
Q3 2SA816 512-KSA940TU
Q4 2SA733 512-KSA992FBU
Q5 2SC869 512-KSC2383YTA
Q6 2SC869 512-KSC2383YTA
Q7 2SC945 512-KSC1845FTA
Q8 2SC945 512-KSC1845FTA
Q9 2SA733 512-KSA992FBU
Q10 2SC945 512-KSC1845FTA
Q11 2SC1384 512-KSC2690AYS
 
I've now replaced all the transistors and caps on the amp board including the drivers. I have not replaced the output transistors yet but have then on hand.

I have also replaced all the caps on the aws-083

Powers up and comes out of protection quickly.

Still the closest I can get to 0mv while adjusting the junction point is -105mv. Both channels are similar.

At this point I'm hoping for a little help. I'm bit sure if I should replace the outputs or test some other voltages first.

Thanks
 
Even if they look like good power supply voltages, I really would appreciate the courtesy of you posting them. Both the regulated and unregulated voltages. I acknowledge that I never EXPLICITLY asked for them on the 23rd.

Basically I need EVERY voltage from EVERY amplifier board pin. There is a HOST of things I will be looking for, including evaluating the output transistors. It WILL get me the power supply voltages.

The amplifier WILL DC balance without the output transistors, but for now leave the output transistors in place for now to get emitter resistor voltages that will tell me some things about their health.
 
So I'm clear what you are asking and how to do it, you are looking for voltages at pins 1-45 and I get these by grounding to chassis?


System running for 10 minutes
1- -.141
2- -.141
3- 0
4- -50.86
5- 0
6- 0
7- +37.12
8- -.141
9- -.234
10- +37.11
11- 0
12- 0
13- -50.8
14- 0
15- -.225
16- +37.3
17- +37.15
18- +45.4
19- -.226
20- +45.4
21- +.285
22- +.285
23- +45.4
24- -.224
25- -.229
26- -45.3
27- -.787
28- -.785
29- -45.3
30- -.230
31- -.140
32- -45.4
33- -.684
34- -.684
35- -.684
36- -45.21
37- -.140
38- -.140
39- +45.05
40- +.392
41- +.392
42- +45.12
43- -.140
44- +45.01
45- +37.38
 
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Grounding to chassis?

plus seeing 0 volts on pins 7 and 35, yet "system running for 10 minutes"...

something's fundamentally wrong here, there is no meeting of the minds.

The DMM black probe is grounded, to a BARE metal chassis ground
the red probe is used to probe the voltages, INSULATE all but the tiniest portion of the tip of the probe
Set the dmm to read volts DC
if the dmm does not automatically switch voltage ranges, select the 200 volt range
take the reading, if it is less than 20 volts switch to the 20 volt range
take the reading, if it is less than 2 volts switch to the 2 volt range

It looks like with your multiple 0 readings, that the dmm is reading 0 because it is overloaded.
 
I grounded to bare metal. There were a couple pins that read 0L, maybe those were overloaded. I set the DMM to MV. It's a fluke 77 so id hope it's accurate.

I'll redo in the morning.
 
I changed the range to volts and updated the results above. My DMM has autorange and figured it would adjust accordingly but I guess not.
 
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