SA 8100 Protection Relay

[Vinty]

My sa 8100 will turn on, play for 5 minutes or so and the protection circuit kicks in. Unlike the problem described in the SA 9100 thread, mine does not pop or make any other noise, just shuts off. Would like some advice as to possible simple fixes to this wonderful, but un serviced piece. Really like this amp so any help is appreciated.

 

[HVHiFI]

Is the protection relay kicking in? Get the service manual for instructions on checking the bias. It is possible you have components failing causing the trouble.

 

[Vinty]

Yes, the indicator lamp comes on and sound shuts off. Changed fuse, same thing. Never checked bias before. Hadn't used the amp in some time and coupled it with a tuner to check it and found this problem. No other components involved. Thanks

 

[HVHiFI]

By components I mean in circuit (transistors, diodes, caps) that can cause the amp to go into protection if failing. Here is the schematic for the power supply. On the left it shows the power rails that should be checked with a DMM to see if they are in spec. See if you can get a SM, that will give you amp alignment instructions.

 

[kirk57]

I have an 8100 also...what speakers are you using when this happens?

 

[Vinty]

An old pair of JVC SK 500's. Happened to be what was handy in my basement. Happen to be the from the first stereo I ever bought.

 

[markthefixer]

HVHIFI - you can't toss a neophyte or new poster into the deep end like that!!

connect the black lead of your meter to a bare piece of the metal chassis (or the gnd pin)
insulate all but the tiniest part of the tip of the red probe for WHEN you slip, we ALL slip!!
touch the bare tip of the red probe to the indicated pin of the indicated board, take the reading,
then post the board number, the pin number, the EXPECTED reading, and finally the ACTUAL reading.
(you can copy the stuff i typed about the pin and the expected reading, and add your actual reading to the end of it)

all readings unless indicated differently, are for DC volts

take thse readings when the unit is in protection,

sa-8100

awe-030 power supply
pin 9 +50v raw
pin 19 +35v
pin 16 +13v
pin 11 gnd
pin 15 -13v
pin 12 -42v

awm-027 protection

pin 2 audio amp out 0.000v
pin 4 audio amp out 0.000v
pin 6 -13v
pin 9 over current protection +0.020v
pin 10 over current protection -0.020v
pin 11 over current protection +0.020v
pin 12 over current protection -0.020v
pin 16 +35v
pin 7 gnd
pin 17v 7.5v AC note: switch the meter to AC volts for this reading, then switch it back to DC volts!!

use the manual to find the boards, they WILL have the aw?-xxx stamped or printed on it somewhere

they are on the underside of the chassis.

power supply board has fuses on it

there ARE problematic transistors that even if testing good, it would be a good idea to replace them proactively.

 

[Vinty]

Thanks, I'll give it a try. This is all new to me so thanks for the patience. I am not only a new poster but my knowledge of electronics repair is limited. I appreciate the help.

 

[HVHiFI]

LoL Mark, your the best. I wish I had half your patience and knowledge.

Vinty, if you listen to Marks directions you will gain such a wealth of information for troubleshooting.

 

[rolleiman]

Hi Guys, hope this not too off track . . .
When basing the SA-8100 it says to terminate the power amp inputs with a 4.7 k resistor. Do they mean to put the resistor across the positive side of the input terminals or do they mean to put resistors between the plus and ground of each (left and right) channel? Thanks again team for your help.

 

[markthefixer]

they mean to put resistors between the plus and ground of each (left and right) channel.

unneeded, just turn volume to zero, the resistors are for engineering / specing absolute tests.

also speaker load resistors unneeded as well.

 

[rolleiman]

Thanks Mark. Much Appreciated!