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SA 9100 Static on left channel - trying to repair need advice/help

S

scottm015

Active Member
I have an SA 9100 that is giving me problems. The symptom at the present is when I turn the unit on it appears to be operating as it shoud but I hear a slight amount of static (pink noise) coming from the left channel only. This static gets louder over time and after 10 minutes or so it is very pronounced. If I give it a source such as my ipod through any of the inputs (did not try phono) the music will play through both channels but the left channel still has a lot of static in addition to the source material and it seems to get louder and louder. I hear the static on Left channel with or without a source. Occasionally the protect circuit will kick in but that is very intermittant and I'm not too concerned with the protect circuit just yet. I have read up on how to fix the protect circuit but have not seen any information on the static from a single channel. The static loudness does not change with the volume control going up and down, it is just constantly there. Could this be a bad output transistor? There are only two output transistors per channel so maybe this will be an easy fix if they are available? I have checked voltages per the service manual on the power supply and they are all within 5-10% of targets. I have set the idle current and neutral potential after 20 minute warm up time and achieved the 25mV and 0.000V per the manuals targets. I replaced the 470uf cap on the power amp board "C12" and still have the same problem. I also jumpered across the relay C and NO for the left channel output to verify that the problem is not in the relay. The static did not change. Any ideas on where I should look and measure further? Thanks
 
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From a casual, and non-expert glance, it sounds like a transistor failing. However, it may not be the outputs, it's probably in the pre-amp section. I think its called cascading. If the noise gets progressivly louder, its almost certainly this, since the failing transistor would get worse as it heats up. Traking down that transistor can be a problem, but not too much of one. Maybe someone with more knowledge of this particular amp can chime in...

I suppose it could be in the power supply (I belive this has a dual supply?), but its less likely than a transistor leaving the mortal coil.

Edit: oh, and good luck, this should be easily fixable, and its worth it, a great amp you have there :yes:
 
I bought this unit after reading so much about it here in the AK forums. It was actually supposed to be a working unit so I was pretty bummed out when it arrived and did not work. I guess this will make me intimately familiar with my new amp if I can just muster up enough patience. I also have a TX 9100 that I will be aligning in the near future and a newly acquired mint PL-55x TT. I just hope I can get this amp to work or my Pioneer setup is kaput.
 
scottm015 said:
I bought this unit after reading so much about it here in the AK forums. It was actually supposed to be a working unit so I was pretty bummed out when it arrived and did not work. I guess this will make me intimately familiar with my new amp if I can just muster up enough patience. I also have a TX 9100 that I will be aligning in the near future and a newly acquired mint PL-55x TT. I just hope I can get this amp to work or my Pioneer setup is kaput.
Click to expand...

Yeah, I had the same thing with my sx-727, advertised as working, not quite. I had different problems, and the main fix was cleaning the volume pot and switches. It seems harder than it is, keep up a little patience, and you'll have a great amp. If it is indeed one transistor going into throws (thermal runaway maybe?), then it won't be difficult past confirming and replacing. If this unit had pre-out jumpers, you could confirm which section it is in. A quick check confirms the pre-out/power-in utility. If you could hook up a different pre-amp, and see if it persist, then you could narrow it down to location.

Sounds like a nice setup, especially the turntable, it's beautiful:yes:
 
Sincde the static is there whether the volume is up or down then it must be in the preamp. True? I should probably stop looking at the output transistor or the power amp board and start tracing the preamp section of the left channel..
 
scottm015 said:
Sincde the static is there whether the volume is up or down then it must be in the preamp. True? I should probably stop looking at the output transistor or the power amp board and start tracing the preamp section of the left channel..
Click to expand...

It would be more likely, I belive. The volume would affect the pre-amp as well, since the volume pot controls the input voltage of the source. Asking my father, far more expierianced than me, he suggested a bad (or cold) solder joint, rather than a transistor. The joint would start bad, and get worse and less connected due to heat. Unfortunately, this could be anywhere, but it is trackable. I'll try to think about it, and maybe come up with something later, or someone who has alot more expieriance will pop in and know what it is...as well as how to track it down...as I haven't actually encountered this type of thing yet (though i'm sure I will:D)...
 
IT'S NOT the preamp!!!!

For some reason we're getting a rash of these. The built in sa-9100 timebomb.

Stop fooling around, risking your equipment, and move the pre-power jack in the back to "separated" and see if the noise continues. If so it's in the power amp.

If you want to check my bona-fides and "expert" status, just read this short thread:
http://www.audiokarma.org/forums/showthread.php?p=3325671

From there it's the same as this thread:
http://www.audiokarma.org/forums/showthread.php?t=270672

The 2sc1451 transistors are the most likely culprit. They have been failing in MANY different manufacturer's equipment - especially when run at elevated voltages and temperatures. The one that are NOT run at 1/4 watt dissipation and 30+ volt's don't seem to have as many problems. And only with some lots - possibly a process problem that has taken this long to show up.

replace them with this:
512-KSC3503estu to-126 ecb 300v .1a 1.2/7w 150mhz 40-320hfe $0.28 ea
from mouser.com

edit: I forgot to say in this thread, that there are two per channel, so get a total of four transistors. I also haven't gotten any feedback as to whether or not the new transistor's leads will fit into the old transistor's lead holes in the pc board. I have a 9100 in the line waiting for work, but since it's mine, it keeps on getting pushed to the end of the line.... otherwise I would know by now about the size of the holes in the PC board for those leads.

Please read the whole thread, there are some mechanically sensitive - IRREPLACEABLE - parts in the way of the getting to the 2sc1451's to replace them, they are called STV-3H's and their leads love to break off flush with the body of the component. If the amp is powered on with one of those leads broken - it will destroy the output transistors and drivers on that channel - probably will also blow the main fuse, and may emit smoke.

The 2sc1451;s that need replacing are the ROUND ones that look like this:
011_goapower_002.gif


while these are repaired (top) and original (bottom) stv-3h or stv-4h diodes (h=horseshoe):
attachment.php
 
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markthefixer said:
IT'S NOT the preamp!!!!

For some reason we're getting a rash of these. The built in sa-9100 timebomb.
Click to expand...

:sigh:...and a sorry for leading this in the wrong path...I hate to give out wrong information, but I guess you have to learn along the way...should probably brush up on devices and see if I don't improve...

and to scottm015, I hope that transistor is all it needs, sounds like that's the case, so good luck:yes:
 
33&athird said:
:sigh:...and a sorry for leading this in the wrong path...I hate to give out wrong information, but I guess you have to learn along the way...should probably brush up on devices and see if I don't improve...

and to scottm015, I hope that transistor is all it needs, sounds like that's the case, so good luck:yes:
Click to expand...


ehhh... you'll get the hang of it. My mantra is to double check before putting my mouth (or fingers) in gear. I have GIGS of online manuals, and use them extensively. Once you study the signal flow diagrams and relate them to the switches and circuits in the units, you will be asking insightful questions to narrow the possibilities...

My buddy watched me do some posting a while back, and shook his head sadly as I pulled up pdf after pdf for model after model, going in directly to a page number and hitting within a page or so off the top of my head for what circuits I wanted to double check before posting an answer.

He said HE wouldn't want to be THAT familiar with a set of documents.
 
Update - I performed a test using the pre out circuit of the SA 9100 and an external amplifier (Hafler DH 200) that is known good. The static is coming through just as before after about 10 - 15 minutes of warm up time it progressively gets louder over time. Does this point back to the pre-amp section?
 
scottm015 said:
Update - I performed a test using the pre out circuit of the SA 9100 and an external amplifier (Hafler DH 200) that is known good. The static is coming through just as before after about 10 - 15 minutes of warm up time it progressively gets louder over time. Does this point back to the pre-amp section?
Click to expand...

Yes, if the speakers are connected to the hafler
<grin, it's a long nite - I'm punchy)

Now you need to manipulate EVERY front panel control to see what effect it has on the static.

The bright (or dim) point is that there are a zillion metal to metal signal carrying contacts in the preamp , and ANY ONE of which (on that channel) can be causing your problem. If you deoxited already, on long time dirty stuff sometimes it takes several tries before you hit good contact material.

If you haven't deoxited, you need to. Stay away from the pots with deoxit until you have faderlube on hand too. Faderlube must be applied to deoxited pots - deoxit removes the vital lubrication. faderLUBE restores it.

Other than that, the results of your front panel manipulation will clarify things somewhat.
 
I was thinking of doing this but all I have on hand is some CRC non residue "QD Contact Cleaner" for electrical parts and CRC "2-26 Multi Purpose Precision Lubricant" which says it improves Electrical Properties. Will these work in place of DeOxit and Faderlube? Thanks for all the help on this. I have gone through most of the voltages on the different boards and all are coming within 5-10% of targets.
 
I had tried to manipulate the controls and none of them seem to have any affect on the static. I think it is still possible to be a problem in the controls though. Can I rule out controls that have effect on both channels simultaneously such as bass and treble or are these controls in paralell so that each channel effect is divided? Just trying to eliminate some of the controls out of the gate.
 
We're talking about 10 minutes of panel twisting, to see if, for example, the volume control affects it, the loudness control, defeating the tone circuits makes it go away etc...

Cleaner cleans away the stuff that prevents the deoxit from attacking the corrosion - which is chemically changed metal - sulphates - I use it to stretch my deoxit - which isn't cheap.....

deoxit loosens the molecular bonds between the sulphates and the unaltered metal, allowing friction of repeated actuation to scrub the sulphates away - resulting in a bright clean streak of metal; on an otherwise blackened surface.

It is a unique chemical formula. Patented I believe... and until deoxit came along, I mourned for the demise of great vintage hi-fi gear. Now I have hope - finding deoxit here on audiokarma was an eye-opener for me.

I don't know HOW many times I have made THIS speech.... sigh.....
 
OK I cannot get the controls to change anything with the static and they could not be any cleaner. With that said I'm seeing some heat coming from the power supply board assy B which appears to be from Q1 - 2SD313P and Q2 - 2SB507P. Each have their own heat sink attached and the temp is going above 150 deg F on both. I'm using an infrared heat gun so it may not be exact but I can feel this is the hottest place on the board. All voltages on the terminals check out though. We already thought this might be related to heat and after 10 - 15 minutes these keep rising. Any thoughts? Maybe a bad Diode, Cap, or resistor in this area causing too much current draw on these Transistors? Why would it look fine on the terminal voltages though? Also The power supply circuit assy A does not show any voltages on my schematic. Does anyone have voltages in another version schematic perhaps or know what these should be since this is only the main rectifier circuit?
 
Here are the measurements to this point; (Format is Actual/Target and all measurements are reference to chasis GND)
Power Supply Circuit-A assy
1. +43.8 Vdc
2. 33.48 Vac
3. -43.8 Vdc
4. 33.5 Vac
5. 45 Vac
6. +56.9 Vdc
7. -57.6 Vdc
8. 44.5 Vac
9. 0 V common

Power Supply Circuit-B assy
1. NA
2. -17.06 Vdc / -16 Vdc
3. -26.30 Vdc / -24 Vdc
4. -13.44 Vdc / -13 Vdc
5. -45.70 Vdc / -42 Vdc
6. -58.60 Vdc / -56.5 Vdc
7. +58.00 Vdc / +56 Vdc
8. +45.30 Vdc / +42 Vdc
9. +37.44 Vdc / +35 Vdc
10. +25.91 Vdc / +24 Vdc
11. +16.87 Vdc / +16 Vdc

Filter Amp assy
6. -26.31 Vdc / -24 Vdc
9. +25.91 Vdc / +24 Vdc

Protection Circuit assy
2. -13.32 Vdc / -13 Vdc
11. -37.06 Vdc / -35 Vdc
12. 7.63 Vac / 7.5 Vac

Control Amp assy
6. +16.67 Vdc / +16 Vdc
8. -16.86 Vdc / -16 Vdc
23. +16.63 Vdc / +16 Vdc
21. -16.83 Vdc / -16 Vdc
15. +16.50 Vdc / +16 Vdc

Power Amp assy (Left Channel)
1. +25.66 Vdc / +24 Vdc
6. -45.60 Vdc / -42 Vdc
8. +45.30 Vdc / +42 Vdc
14. +43.80 Vdc / +45 Vdc
9. -2.0 mV to -7.0 mV fluctuating / +11.0 mV
13. -11.0 mV / -16.0 mV
11. -43.80 Vdc / -45 Vdc

Power Amp assy (Right Channel)
1. +25.96 Vdc / +24 Vdc
6. -45.70 Vdc / -42 Vdc
8. +45.40 Vdc / +42 Vdc
14. +44.20 Vdc / +45 Vdc
9. +2.0 mV to +9.0 mV fluctuating / +11 mV
13. -10 mV / -11 mV
11. -44.10 Vdc / -45 Vdc

Equalizer Amp assy
6. +25.73 Vdc / +24 Vdc
8. -26.17 Vdc / -24 Vdc
 
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I have nothing but respect for the ones who work at component level and I appreciate you guys helping me through this. Please let me know if you see anything out of the ordinary with the above measurements. Keep in mind the left channel is the problem at the moment and occassionally I get the protection fault kicking in but right back out so I'm not too concerned with that at the moment. If all the measurements look normal then I will order some deoxit and faderlube and whatever else you guys think I need - Oscillioscope (actively looking for an Oscope), Fgenerator, Xray machine... JK Honestly I'm committed to making this amp perform as new and I hope it will happen so please feel free to share your advice with me.
 
Also need to add that while testing today with the volume turned up that the Phono section has a hum. I have no TT hooked up to the unit though so maybe this is normal. Also the Subsonic switch makes a lot of pop when switching. Other than that there are no changes to the static in left channel while manipulating the controls. so I have static whether I'm in preamp mode or if the 9100 is driving speakers and when changing any of the controls for the preamp section including the volume, the static does not change. I'm thinking I can rule out the internal power amp and preamp sections and start targeting the power supply circuits A and B?? If each channel has it's own PS then maybe this is the problem after all. I'm about at the end of my rope with this unit. Maybe I just need a break :) Looks like I'm the only one posting here..
 
Life intrudes, I have guests over on Sunday afternoon and evening. They're STILL here...

Can you trust me if I say it's not the power supply, and that those numbers all look good?

Put the pre-out / amp-in switch to separated to see if the amp still goes into protection - the rationale is to see if the preamp is spiking the power supply bad enough to push it into protection.

The 9100's signal diagram is a bit deficient, so it will take a bit of work to find the source of noise that can be generated that isn't affected by any controls.

For example it is obviously past the volume and balance controls, but I have to see if the tone bypass switch does a COMPLETE bypass or if a bit of circuitry is left active, and whether or not any active devices in the low and high filters are completely bypassed when they are off.

edit:
pins 13 & 16 are inputs to the control amp, and pins 2 & 27 are outputs - BUT there's a LOT of switch contacts in between to sort out.

look for noise on both the inputs and outputs.If youi don't know how to, you will need to wait until a signal probe is explained or linked to.
 
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