Hey guys, I am working on my AU 20000 because my protector light is on, my RL01 relay is not clicking at all when powered on but the RL02 clicks and stays on, I was reading the service manual and they mention when there is no activity at the RL01 that the posistor PR01 on the F-2509 board coul'd be deffective? Where is this board located?? And what should I be looking for! Thanks in advance guys!
Sansui AU - 20000 PR01 on F-2509???
- Thread starter Todd1985
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It prefaces that comment with "When the Power transistors Overheat" - don't read too much into the Service Manual troubleshooting procedure.
PR01, type PTH487A is a positive temperature coefficient thermistor and will be located on or near the output transistors. Usually they look like a yellow or brown 'blob' on what looks like a solder tag. Try not to interfere with them as, they are NLA and it is difficult to find replacements, additionally they are not prone to failure. Note that the stiff wire leads are extremely brittle, and break very easily thus rendering them useless.
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Ok, and the power transistors are the silver caps inside the heat sinks?
Your reply suggests that you have limited electronics experience, am I right?
You are correct lol, but I'm pretty sure I can figure it out with some help on this forum! I've been studying this unit for a few weeks already, the one I have is nearly mint condition and was stored in its original packaging for about 30years! Im pretty sure it's not much throwing it in Protection mode...
OK, enthusiasm is a wonderful thing 
- and it's true a protection mode problem can be a simple thing to remedy initially. However, what comes afterwards with an amplifier of this age is the difficulty that relative novices will experience, because it will need a pretty thorough restoration to work reliably - not an easy task.
The AU-20000 is a large, complex and powerful amplifier and you will need to know 'how to read a schematic', 'how to use a multimeter effectively to fault find', and 'know how to solder without damaging the printed circuit boards or components' - to name just the basic skills needed among many required when fault finding and restoring one of these amplifiers.
The protection fault might be remedied by simply performing the DC Offset settings procedure in the Service Manual. Which I have just been reading on page 3, You will need to do both channels, and obviously you need to know how to use a multimeter for this procedure.
- and it's true a protection mode problem can be a simple thing to remedy initially. However, what comes afterwards with an amplifier of this age is the difficulty that relative novices will experience, because it will need a pretty thorough restoration to work reliably - not an easy task.The AU-20000 is a large, complex and powerful amplifier and you will need to know 'how to read a schematic', 'how to use a multimeter effectively to fault find', and 'know how to solder without damaging the printed circuit boards or components' - to name just the basic skills needed among many required when fault finding and restoring one of these amplifiers.
The protection fault might be remedied by simply performing the DC Offset settings procedure in the Service Manual. Which I have just been reading on page 3, You will need to do both channels, and obviously you need to know how to use a multimeter for this procedure.
OK, enthusiasm is a wonderful thing
The AU-20000 is a large, complex and powerful amplifier and you will need to know 'how to read a schematic', 'how to use a multimeter effectively to fault find', and 'know how to solder without damaging the printed circuit boards or components' - to name just the basic skills needed among many required when fault finding and restoring one of these amplifiers.
The protection fault might be remedied by simply performing the DC Offset settings procedure in the Service Manual. Which I have just been reading on page 3, You will need to do both channels, and obviously you need to know how to use a multimeter for this procedure.
I'm aware this is a complex unit, I'm willing to try the best that I can because a repair shop around here does not exist. I'm able to use a multimeter and can solder! So please could you explain the procedure and I can go ahead and give it a try?
As you may have realised, because the unit is in protection mode, RL01 (speaker relay) contacts have not closed, therefore the speaker terminals are not connected yet. So in order to measure DC Offset (with protection mode engaged), you will need to find a point before the speaker relay contacts in order to measure the DC offset and adjust it (hopefully).
There are various points where the DC offset can be measured in this situation, but I am not sure how accessible these are never having worked on an AU-20000.
Pins 18 & 19 (for left and right channels) on the F-2511 Protector PCB seem to be the obvious choice, accessibility permitting. Measure between each of these pins and ground, and adjust accordingly. The protector PCB has 2 Relays on it, RL02 which is the soft start relay, and RL01 which is the speaker relay - Note: there are mains voltages on this board especially around RL02 - be careful!
OR, on the F-2497 Emitter resistor board - where you will find 6 white ceramic emitter resistors on each of two of these boards, measure between where they all connect together, to ground for each channel, and adjust accordingly.
There are probably other places where these connections might be available, there may be an easily accessible place, but I would think those who have worked on one (not me
) would know where that is. It goes without saying that slipping with your probes, and shorting something out, while measuring can seriously damage your amplifier. Rather than standard meter probes, most here use 'mini-grabbers' which are meter leads which have spring loaded 'hooks' to securely attach them to contact pins or component leads. These are far safer, so to continue with this, I strongly advise you to get some. 
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Nothing connected to any input or any output (no speakers), and as you have noted above.
Good luck!
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Ok, got the ground figured out! So tested pin 18 and geting -15mV and on pin 19 getting -196mV. So im guessing this meens there is a short higher up? Would taking the F-2497 boards out of the heat sinks and doing testing there be the next step or would you have another suggestion?
Yes, that would be OK - but be careful with assuming what is 'ground' - just in case pin22 itself has a bad connection for example - best to choose anywhere convenient on the chassis as ground.would pin 22 on the f-2511 be my ground?
You say you get -15mV at 18 and -196mV at 19 are these voltages the readings after you have adjusted the DC offset? - as it should be adjusted to as close to zero V as possible.
Also your protection relay RL01 should be energised now, and the amplifier not in protection mode, as neither of those DC offset voltages are enough to trigger protection.
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Alrighty, so what I did I used the ground directly on the chasis where pin 22 was mounted.
Now for the readings I got I did not touch the DC offset settings yet? Should I? If so, I assume I would I need to adjust them by turning them clock wise??
Would you mind explaining How I test this RL01?
Now for the readings I got I did not touch the DC offset settings yet? Should I? If so, I assume I would I need to adjust them by turning them clock wise??
Would you mind explaining How I test this RL01?
RL01 should be energised, because those DC offset voltages are not enough to trigger protection mode - which is when the relay is not energised.
So if the amplifier is still in protection mode - you have a protection circuit problem. It is unlikely that the relay is faulty, as the front panel light is flashing (?) indicating a problem - if the light had been steady, but RL01 still not energised, then I would say RL01 may well be faulty - but this does not appear to be the case. (IF the protection light is flashing?).
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Well the light is steady on my friend.... so maybe just faulty relay?? But should I try to bring my values at pin 18 and 19 to as close to 0 mV either way?
No need to do that right now.
But
I have just realised that this amplifier has a protection light that comes on when in protection mode and goes off when not in protection mode - the lamp itself having no flashing behaviour - as many other Sansui amplifiers do.
So, protection light on but no RL01 activation, could be something wrong with the protection circuit transistors TR03, TR04 (the relay driver transistor), or TR05 - or back to the original question of a faulty or damaged thermistor, OR something wrong with the supply voltage to the relay - should be 25V - maybe it is too low to energise the relay - but IS enough to illuminate the protection lamp.
I have no idea how accessible the protection board is on this amplifier, but you could try to do a visual check on the famous Thermistors (see my first post) - of which there are two - one on each output assembly. - have a go at that, this fault could after all, be visual.
Like this
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