Need schematic Technics SA-918

This is for a good customer who wants this toilet fixed for sentimental reasons (so he says). It has a shorted STK4152II that's putting the -Vcc on the speaker terminal on one side, the other side is working. There are no relays of any kind in this receiver and I can't believe there isn't some sort of speaker protection scheme incorporated, not even speaker fuses. Even Pioneer's suicide circuit was better than nothing at all.

Anyone have a schematic for this? Also, the STK4152 is a discontinued device, but there are plenty out of Hong Kong. Anyone use one of these generics recently and had good success with it?

 

[N_Cook]

On 30/11/2016 16:58, ohger1s@gmail.com wrote:

This is for a good customer who wants this toilet fixed for sentimental reasons (so he says). It has a shorted STK4152II that's putting the -Vcc on the speaker terminal on one side, the other side is working. There are no relays of any kind in this receiver and I can't believe there isn't some sort of speaker protection scheme incorporated, not even speaker fuses. Even Pioneer's suicide circuit was better than nothing at all.

Anyone have a schematic for this? Also, the STK4152 is a discontinued device, but there are plenty out of Hong Kong. Anyone use one of these generics recently and had good success with it?

I tend to use a pair of TDA7293 in these situations STK/TA hybrids,don't
know specifially for that STK, bending up pins and rewiring in to suit.
Sometimes you need to invert the mute line control though

 

Those knockoff ICs are almost never good. Real NOS is hard to find.

I couldn't find the print on the receiver but the chip is only 30 WPC which means you can use a couple of LM3886s in it, just figure out how to remount, use the inverting and non-inverting, hook up the power and the speakers, and you need a resistor to the muting line. Get them clamped to the heatsink and you should be alright. I did that on a Mitsubishi X-11 system. I almost wanted to just put preamp outs on it and tell the guy to use an external amp but they put the tone controls in the output feedback so they would not work unless I got some OP AMPs and this was just a better solution. Just hook up the speakers and you are good to go.

Cook wants to rebend pins but what I did was to turn the upside down and simply wire the pins to the board where needed. That way the pinout doesn't even have to come close. Ad the LM3886 is a six wires solution, and one of those is the muting and only requires like a ten K resistor which can easily do both channels. Don't even entertain the idea of leaving the working channel in there. Too much PITA and for no good reason.

 

On Wednesday, November 30, 2016 at 11:51:24 PM UTC-5, jurb...@gmail.com wrote:

Those knockoff ICs are almost never good. Real NOS is hard to find.

I couldn't find the print on the receiver but the chip is only 30 WPC which means you can use a couple of LM3886s in it, just figure out how to remount, use the inverting and non-inverting, hook up the power and the speakers, and you need a resistor to the muting line. Get them clamped to the heatsink and you should be alright. I did that on a Mitsubishi X-11 system. I almost wanted to just put preamp outs on it and tell the guy to use an external amp but they put the tone controls in the output feedback so they would not work unless I got some OP AMPs and this was just a better solution. Just hook up the speakers and you are good to go.

Cook wants to rebend pins but what I did was to turn the upside down and simply wire the pins to the board where needed. That way the pinout doesn't even have to come close. Ad the LM3886 is a six wires solution, and one of those is the muting and only requires like a ten K resistor which can easily do both channels. Don't even entertain the idea of leaving the working channel in there. Too much PITA and for no good reason.

LOL! I'm not going to invent the wheel on this thing; it's not worth time, sentimental reasons be damned. At the end of the day, I still have to bill by the hour. A cheaper solution which I've used in the past is to buy complete used receiver on ebay for parts.

My questions were if anyone had successfully used the currently available STKs and this indeed has no protection scheme (hence the request for the print).

In any case, I'm sure one of the Nesda members has an OEM STK somewhere and I'll post a request there if I'm not confident one of the currently available STKs are not suitable.

Thanks for the advice guys.