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Au-666 Protection Block 1RC5 Replacement Diodes??

zastin17

zastin17

Active Member
I am just about done rebuilding a Sansui Au666.

I have replaced almost every single Transitor! Including the Outputs. This thing has a terrible failure at some point!!!

I was battling some strange DC wonkyness on the output. Common to both channels.

Turns out, 1x IRC5 Diode ""thing"" is fully shorted. While 1x is ok.

I removed the entire protect PCB. I connected the speakers directly off the Fuse. And the the SOUND IS ABSOLUTELY PERFECT!! Bias is stable, cool, ect. Same for Offset.

This part I cannot find anywhere!! No cross references or anything!!

Any modern part I can use to replace them with?? I rather enjoy this Sansui as stock, though I know the protection has no effect on sound.

Here's the IRC5s on the Schematic!!

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That's a silicon controlled rectifier made by International Rectifier way back in the day. I also struck out on finding a specific cross save for NTE5452 which is a 30V rated device. Hopefully someone who has previously had to replace one will be along to advise.
 
basically, the diode does nothing special except for rectifying possible DC voltage, so any generic diode which does fit will be good.

:biggrin: "Most will use the 1N4148 diode I think, because I think the diode 1N4148 is the one used most" :D


btw google SR1FM2 gives a direct hit to datasheet sites, it is a Mitsubishi 80V 1A diode

I replaced the circuit by a relay type of thing in my AU666 myself, so I do not use the circuit, anymore.
 
These devices ('SCR' means Silicon Controlled Rectifier), are used in Sansui's implementation of a Crowbar Protection circuit. The idea is that if too much voltage is seen on the power amplifier outputs (either or both), this will energise the protection circuit, which will trigger (either or both) thyristors which will turn hard on, and blow the quick acting 4A fuses F001 and/or F002, off to the left and not shown in your schematic snip. This has the effect of disconnecting the speakers which might otherwise suffer damage due to application of DC voltage. They can be triggered if the music output is too high (overdriven), OR if an output transistor fails (for example) and applies high voltage to the speaker terminals.

As already suggested they don't need to be high voltage devices, (30V is fine) but they do need to be capable of passing enough current to blow the fuses, at least 4A. I am a little puzzled that the bridge rectifier composed of 2 pairs of 10DC-1 are only rated at 1.8A each, suggesting a capacity of only 3.6A under fault conditions. :idea:

This is about all I could find in a wire ended component that is anything close to the spec of the originals, it's a 6A, 400V device, which will work just the same as the originals. It seems lower voltage devices are all either obsolete, or are SMD devices. :(
https://www.mouser.co.uk/ProductDetail/Littelfuse/S4006VTP?qs=zHiv0nsVGmqnk5TbJRGEWw==

Note that when triggered these devices (Thyristors) 'latch on' so the only way to turn them off is to briefly turn the unit off. (or short the anode to the cathode). This behaviour was seen as a further safety feature forcing you to seek service for your AU-666 if these devices are getting triggered by a fault. :)
 
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