Pioneer SA-8100 Half volume protection

[redcbx78]

I recapped the SA-8100 and upgraded/replaced key components on the protection board, etc. as found along various threads on audiokarma.

The amps sounds great, all controls work fine, but once I reach about 50% volume the 8100 will go into protection. If I turn the volume down, it will come out of protection. I did adjust the offset and bias to spec.

I don't know if the unit had the same behaviour before recap/upgrade.

Any help would be appreciated.

 

[markthefixer]

In upgrading key components etc, on the awm-027 protection board, exactly WHICH components did you change, and with what.

I suspect q1, q2, but have to know what the values of C1 and C2 are... little green 0.056uf caps or little blue 0.22uf caps? Can probably get away with using ksc1845's in either case, but we have to figure out if it's the older or newer production model.

 

[redcbx78]

I do know I have Revision A of the awm-027, which did not quite match the schematic found in the service manual. I'll post exactly what I changed and possibly a picture or two.

Thanks

 

[redcbx78]

Awm027 d

I have the AWM-027D in my 8100.

The following is what has been replaced on the AWM-027 D

C1,C2 : .22uf electolytic : .22uf 50v Panasonic Film
C3,C4: 330uf 6v : 330uf 10v
C5 : 4.7uf 25v : 4.7uf 50v
C6 : 100uf 16v : 100uf 35v
Q1,Q2 : 2SC869 : KSC1845FTA
Q7 : 2SC1384 : KSC2690AYS
Added 1n4004 across pins 14 and 15 of AWM-027 Protection Board

I did a full recap including the main filter caps. All caps were replaced with same uf value, but a step up in voltage rating.

All power supply voltages as well as idle current and neutral potential were spot on.

 

[redcbx78]

Added note, the 8100 with no load - speakers disconnected - goes into protection at half volume - same as when speakers are connected

 

[markthefixer]

do the q3 and q4 with ksc1845 too. unusual, you covered the usual suspects with q1, q2, c1, c2 ....

after that we see which diode on the protect board is carrying the signal by selectively disconnecting them in a particular order,

You ARE off the DBT, right?

 

[redcbx78]

Replaced Q3, Q4 with ksc1845 - same results- protection light comes on at about half volume. Turn volume down comes out of protection - with or without speakers connected.

Engage the loudness button, protection light comes on earlier.

Not using the DBT.

Thanks!

 

[SolutionRoom]

One of the 9100 amps I had did this too, but only with no load (no speakers attached). Once the speakers were connected, it no longer went into protection. So... I did not chase it down any further, as the amp sounded fine. I no longer own this amp now though.

 

[redcbx78]

All is well as long as I don't get up around 50% volume - then protection kicks in. It sounds great, but just can't get past 50% volume. The behaviour is the same with or without speakers. I only normally listen at about 25% volume through my HPM-100's but on occasion................

 

[markthefixer]

Ok, q1, q2, q3 and q4 are all ksc1845.
q5 original?
q6 ksc2383?
q7 ksc2690?

C1 and c2 replaced with 0.22uf stacked film caps.
C3 and C4 replaced, AND installed NEGATIVE to NEGATIVE? This is very important...


just for giggles, disconnect the signal source (to get quiet) and THEN turn the volume control up past the halfway point with no speakers, and see if THAT trips the protection.

Next go to the awr-030 power supply board with the fuses onboard, and take this (almost unnecessary) step: pin 1 of the board has a blue wire, and then it goes to the solitary 1 amp fuse by the corner. pry loose one end of the 1 amp fuse and set it up like a primitive knife switch, after the unit is turned on (the protect should NOT activate) then touch the end of the fuse down and wait the timeout interval for the relay to kick in. wait a few seconds, then let the fuse up to break the circuit, and the protect relay should open INSTANTLY... That checks the first and second stages of the protect board. Put the fuse back in when done.

Then, with power off:

Disconnect one end of D5, let it stand up in the air a bit over the board, this will disable the over current input from Q1, Q2

disconnect one end of D6 AND D7, also let them stand up in the air a bit over the board, this will disable the DC voltage detector.

Then see if it disconnects/trips at the volume point without speakers....

If it does NOT, reconnect D6 and D7 and see if it does or doesn't.... (this still leaves D5 open)

post results and do not use until next answer.

 

[redcbx78]

Results

Mark,

Here are the answers to your questions and the results the tests.

q1, q2, q3 and q4 are all ksc1845 --YES
q5 original? - YES - NEC SA733
q6 ksc2383? - NO - ORIGINAL - SC945
q7 ksc2690? - YES

C1 and c2 replaced with 0.22uf stacked film caps. - YES
C3 and C4 replaced, AND installed NEGATIVE to NEGATIVE? - YES


With no speakers, no input - does not trip

Lifted solitary 1amp fuse, powered on. Unit does not show power or protection.

Pushed 1am fuse down, power light and protection light come on, and then in just a few seconds, protection light goes off

Lifted 1amp fuse - immediate protection mode.

Lifted one end of D5, D6, D7

Turned unit on and with speakers and input - does not go into protection

Reconnected D6, D7, (D5 still lifted) - does not go into protection.

Since almost all transistors have been replaced - should I replace Q6? I do have a KSC2383YTA.

Thanks

 

[markthefixer]

q6 replacement when you are in soldering is prudent precaution, but it doesn't need a special trip. Q6 has multiple functions, but the end result is that IT causes the shutdown on protect, ALL protect inputs.

The rub is that it discharges the timing capacitor, and there's a 22 ohm resistor to share some of the heat load and slow down the draining of the energy charge. The REST of the heat pulse ends up IN the little itty bitty transistor die, and cannot be "spread around" quickly enough - to the transistor's case, the air etc... so ** poof ** This is called "safe operating area".
This kind of wears on that transistor (the heat pulses) and eventually it fails. (it's at the ragged edge of undersized, I like a wider safety margin than they used in the design)

AND NOBODY NOTICES!!

because the turn on delay is still there, and on power off the relay drops just milliseconds later, so maybe there's a thump.
But the IMPORTANT stuff, DC voltage and over current protection? NOT any longer!!!

Ok, now with D5 lifted, and it NOT going into protection, we are back at Q1 and Q2 of the over current sensors.
We've got new caps, we've got new transistors. That leaves the diodes. VERY unusual. D1, D3 left channel, D2, D4 right channel, do all 4 since we don't know which channel it is (you could find out using the balance control)
Mouser's 512-1n4148 (also called 1n914) very common and general purpose.Radio Shack stuff, to save you postage.

 

[redcbx78]

I went ahead and replaced Q6 with a KSC2383TYA - and the 8100 stays in protection mode all the time.

I'll put the old transistor back in and then try the right and left balance, just have some more testing - hopefully only one side will trip the protection.

 

[markthefixer]

I went ahead and replaced Q6 with a KSC2383TYA - and the 8100 stays in protection mode all the time.

I'll put the old transistor back in and then try the right and left balance, just have some more testing - hopefully only one side will trip the protection.

ksc2383 = e c b left to right, lettering facing you and leads pointing down

Check the negative voltage on c5 minus...

 

[redcbx78]

Yup, the ksc2383 was in correctly. With old SA733 in - voltage on negative side of c5 = -4.36 volts.

With q5 = SA733 power on - no input - volume at zero out of protection:
Base: 19.42v
Emitter: 17.19
Collector: 18.19
C5 Neg side :-4.36v

Q5 = KSC2383 power on - no input - volume at zero voltages are and protection is on
Base: 1.22v
Emitter: 1.7 slowly increasing
Collector: .72v
C5 neg Side: -3.82

Now I'm confused............:scratch2:

 

[markthefixer]

How are you determining where the leads go in the board. The a733 could be ebc...

WAITAMINNIT!!! what's this about q5. q5 does not change,
you talk about putting in a pnp AND an NPN in whatever position...


q5 is a pnp "logic" level shifter.

2sa/ksa and 2sb/ksb transistors are PNP

2sc/ksc and 2sd/ksd are NPN transistors.

perhaps you have the transistor positions on the board confused.

 

[redcbx78]

Yup, my screwup. Q5 is back to normal with the SA733
Q6 has been replaced with KSC2383YTA - unit comes out of protection.

I'll test and if still in protection at 50% volume, I'll change out the suggested diodes.

Thanks again!

 

[redcbx78]

Mark appreciate all the help. Q6 replacement did the trick. Cranking AC/DC while I type this.

The one transistor that I did not replace............... But with your help I now have a practically new protection board.

Thanks again!

 

[redcbx78]

Once again I would like to give a BIG thanks to Mark. Been cranking my 8100 today - hasn't skipped a beat. Now on to my 9100!

 

[markthefixer]

You STILL have to re-install D5 and get the over current protect working (new diodes)??

Q6 was a PRECAUTION, disconnecting D5 was a TEMPORARY, TROUBLESHOOTING STEP!!

q6 replacement when you are in soldering is prudent precaution, but it doesn't need a special trip. Q6 has multiple functions, but the end result is that IT causes the shutdown on protect, ALL protect inputs.


Ok, now with D5 lifted, and it NOT going into protection, we are back at Q1 and Q2 of the over current sensors.
We've got new caps, we've got new transistors. That leaves the diodes. VERY unusual. D1, D3 left channel, D2, D4 right channel, do REPLACE all 4 since we don't know which channel it is (you could find out using the balance control)
Mouser's 512-1n4148 (also called 1n914) very common and general purpose.Radio Shack stuff, to save you postage.