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Sansui 8080 Service Mod - Need Guidance

The fuse element of the 'fusibles' was a flop. Increase the resistors power rating and the weakest link may become the semi-conductors that don't usually get fried on a driver amp fault.
 
cecilk said:
Is there any reason the 4.7Ω wirewound fusible resistors mentioned above would not be suitable to use? Since I have them in stock...
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The 1/2 watt won't blow if they need to. But 1/4w metal film will toast in case there is an overload situation and act like a fuse. The concept of using 4.7 Ohm fusible in place of a jumper is that they add very little resistance to the circuit, but just enough to heat up and blow like a fuse. That is the reason they were metal oxide to take the heat but over time whatever they used as the fusing element just drifted higher and higher in resistance and got hotter and hotter until they failed. That is why the colors faded out too, from the heat. Modern fusible resistors are way better and actually blow without any visible signs except for maybe a tiny crack.
 
Wonder why the factory had put jumpers in these positions on this board.

I guess if purpose was to act as a fuse (and not necessarily to add 4.7 ohms of resistance), a piece of 24 awg wire is basically a 3.5-4A fuse, yes?
 
cecilk said:
Wonder why the factory had put jumpers in these positions on this board.

I guess if purpose was to act as a fuse (and not necessarily to add 4.7 ohms of resistance), a piece of 24 awg wire is basically a 3.5-4A fuse, yes?
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No. In theory there is no need for a fusible element for function under normal circumstances. But later noted cascading failure points under warranty when something went awry. (think over cranking and abuse) That's why later versions were produced with the fusible resistors in place of a jumper, and in other vulnerable areas to help protect parts of the circuit and limit the damage. Besides, the driver transistors would smoke if current exceeds their rating, short, and cause further damage. 3.5-4A is way above the transistor rating..
 
hi i apologize but i have a question my board has noting at the back of it and i am not able to figure out where to install or connect R 901 and 902, i am trying to update my 8080.

thank you
 
^ these are 18KΩ resistors. They mount on the back of the PCB. Post #18 has a photo, which you can use for reference.
 
It's basically between collector (lower heat sink soldering pad) of TR13/14 and the emitter of TR-11/12 (upper soldering pad of R47 and R48).

2wGpILp.jpg
 
Hi Tom Greatly appreciate your help will solder it.

i also check post #18 it also has a jumper on the back which is not on my board?

thank you.
 
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hi every one this may sound silly, when i watch videos on 8080, when it is turned the red light flashes an then turns green, my receiver goes form red to green instantly is that ok?
 
Thank you Tom for all your help yes very close to 0 just my meters swing when i turn them on and they all is fine
 
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