SA-8500II mode switch not working right

This amplifier has a problem I'm hoping some fellow Pioneer lovers can help me with. It's working great, offset's under 4mV on each side but when the mode switch is set to STEREO only the left channel works. Here are the rest of the mode switch settings and the their corresponding effect:
REV- right channel works but not the left
L+R- both channels work
L- both channels work
R- neither channel works
I'm assuming that I'm only getting sound in mono and not stereo by having it set to L+R, since that is supposed to be a mono setting. The amp sounds great but I can't tell if it's playing in stereo or not. Regardless, the mode switch is definitely not working right. Thanks for any ideas!

Just doing some checking and now I see that the mode switch is working in STEREO when I play a CD and have the function switch on AUX. I can hear that the sound is definitely in stereo too. Any idea why the mode switch would work fine on AUX but not on TUNER?

Try deoxiting the mode switch...... (and everything else for that matter)

deoxit protects against, as well as cleans up, oxidation.

Thanks Mark. It really didn't seem like it could be a dirty or oxidized switch because the STEREO mode switch setting works fine when I have the function switch on AUX. I'll try some DeOxit anyway and let you know if that does the trick.

mea2112 said:

This amplifier has a problem I'm hoping some fellow Pioneer lovers can help me with. It's working great, offset's under 4mV on each side but when the mode switch is set to STEREO only the left channel works. Here are the rest of the mode switch settings and the their corresponding effect:
REV- right channel works but not the left
L+R- both channels work
L- both channels work
R- neither channel works
I'm assuming that I'm only getting sound in mono and not stereo by having it set to L+R, since that is supposed to be a mono setting. The amp sounds great but I can't tell if it's playing in stereo or not. Regardless, the mode switch is definitely not working right. Thanks for any ideas!

Just doing some checking and now I see that the mode switch is working in STEREO when I play a CD and have the function switch on AUX. I can hear that the sound is definitely in stereo too. Any idea why the mode switch would work fine on AUX but not on TUNER?

Click to expand...

That SA-8500II is on my bench now, and here's a neat little tidbit for the Pioneer guys, the tuner and aux inputs have a 47 ohm 1/2 watt 5 % metal film resistor in series with the input leads from the RCA plugs. When the tuner input (or the aux input ) is NOT being used there is a dedicated switch wafer that GROUNDS the other side of that 47 ohm resistor. Probably to kill any possibility of crosstalk.

Well a former owner of this SA-8500II fed wayyyy TOO MUCH voltage into the tuner input while it was grounded, not only carbonizing the resistors, but almost burning THROUGH the P.C. board!!!

So no amount of deoxit would have got that tuner input working. One channel's burned up resistor was reading 150 ohms, and passed a signal, but the other channel's burned up resistor was an open circuit, i.e. NO signal was getting through, exonerating the mode switch.

As an interesting note, when I inspected the function switch for damage, there was a clean semi circular arc on the rotating switch element, the result of the previous deoxit treatment. It was literally black and white.... The contrast impressed me.

Of course it is now sporting a new set of 47 ohm 5 % 1/4 watt metal film resistors.... instead of 1/2 watters, so they blow sooner and cause less damage.

Thanks a lot Mark! I guess that saying really is true that "good techs never sleep"!! Seriously, just wondering how the previous owner fed too much voltage into the tuner input? I don't want to make the same mistake in the future.

Defective tuner, perhaps tube type with leaky coupling caps?

I'm not really sure....

An incredibly bad wiring error? It takes a lot of energy to do this:

Wow. That is ugly! It's good the whole board didn't have to be replaced.

SA-8500-II alternate transistor mounting scheme

Well this amp has gotten the full treatment. Originally it came in for a bias diode replacement. With the added observation that the tuner input didn't work.

The diode was replaced, and the tuner input problem has been documented in earlier posts.

But a few other things turned up.

One was that the bass turnover frequency selector switch (100 Hz, 200 Hz, 400 Hz) was busted, it was literally MISSING part of one channel's wafer! One attached picture shows an internal toggle switch (on,off,on) that selects the three frequencies, temporarily inserted until a replacement is obtained, after which it can be untraceably removed. The works of the rotary switch were left installed for appearance sake.

Then came the fun when the bias setting procedure was attempted. The bias is set on one of the two pair of output transistors for each channel at 30 milliamps, which when read across 1 ohm's worth of emitter resistance gives 30 millivolts. Then the other pair is checked for 30 millivolts plus or minus 10 millivolts.... so anything between 20 and 40 will (grudgingly) pass.

They never got there, on both channels I estimated to have 30 millivolts on the insensitive pair, over 100 millivolts would have been needed for the other pair. That's BAAAAD...

Thus NEW OUTPUTS were NEEDED... Bad news, the case style on these transistors (2sb617a & 2sd587) has become rare. They mount into a socket, with the collector connections being picked up by the TWO mounting screws, one on each side.

Enter some mechanical engineering; a retainer bar that matched the sockets, and hold down TO-220 transistors, in this case good old ON-SEMI MJE15032 and MJE15033 's. To get the collector connection, there is a LUG LOCKING TINNED#4 terminal attached to the center of the retainer with a 4-40 screw, and the collector lead is bent up into the terminal and soldered to it AFTER the transistor is securely mounted (to avoid strain on the lead). The base and emitter connections are still made through the socket.

THUS with this bar THERE ARE NO MODIFICATIONS DONE to the original heatsinks, unlike in this other thread. The bar is 1/8 inch thick aluminum 1.100 x 0.500 with 2 holes to match the original (horrid little) 2sb617a & 2sd587 's and a tapped hole in the center for the solder lug.

Once the ON-SEMI's went in, and the bias adjusted, the second pair on each channel were within 0.1 MILLIVOLT without adjustment. Pretty good!!!

edit On-Semi also has tip41's:
TIP41CG (NPN) and TIP42CG (PNP). These are 65 watt devices in a TO-220 package.
863-TIP42CG pnp to-220 bce 100v 6a 65w 3mhz 30-75 hfe:100 $0.70
863-TIP41CG npn to-220 bce 100v 6a 65w 3mhz 30-75 hfe:100 $0.64
compared to:
863-MJE15033G pnp to-220 bce 250v 8a 50w 30mhz hfe:70 $0.87
863-MJE15032G npn to-220 bce 250v 8a 50w 30mhz hfe:70 $0.87

edit2, 10-08-09 :
(more powerful to-220 batwing replacements
edit3 6-27-2014 these are obsolete :tears:
512-FJP1943OTU pnp to-220 bce 230v 15a 80w 30mhz 80-160hfe $1.21
512-FJP5200OTU npn to-220 bce 230v 15a 80w 30mhz 80-160hfe $0.85
edit3 6-27-2014 these are obsolete :tears:

edit4, 3/1/2015 nope, the NUMBER was obsolete, here's a new number!!:
512-FJP1943RTU pnp to-220 bce 230v 15a 80w 30mhz 35-160hfe
to-264 2sa1943/fjl4215 150 watts
to-3p 2sa1962/fja4213 : 130 watts
to-220f fjpf1943 50 watts

512-FJP5200RTU npn to-220 bce 230v 15a 80w 30mhz 35-160hfe
to-264 2sc5200/fjl4315: 150 watts
to-3p 2s5242/fja4313: 130 watts
to-220f fjpf5200: 50 watts

edit 5-30-2021
512-2SC5200OTU
512-2SA1943OTU
hfe classification:
R = 55 to 110
O = 80 to 160
end edit 5-30-2021



original sa-8500ii
2sb617a pnp batwing bce 120v 6a 70w 80hfe 14mhz
2sd587a npn batwing bce 120v 6a 70w 80hfe 14mhz

original sa-9500ii
2sb618a pnp batwing bce 150v 7a 80w 80hfe 14mhz
2sd588a npn batwing bce 150v 7a 80w 80hfe 14mhz