AU D11 II in protection mode

djef

Active Member
I was wondering if anyone could help me figure out and fix a Sansui AU D11 II. I push the power button and that red light just flashes and flashes, never coming out of protection. I'm aware of the unique complexity of this amp in particular. I've already gone through it and replaced every single capacitor. I've tested many of the resistors, especially around the protection circuitry, and they all seem to be in spec. I'm thinking it might be the relays themselves, so I'm considering ordering new and replacing them. Does anyone have a substitution relay they'd recommend? I think Panasonic discontinued the original relays.
Any help solving this baffling puzzle will be appreciated.
 
Have you set the DC offset??

Its a long winded process which requires great patience.
Also I would replace all the DC offset trimmers with multi-turn to make it easier to adjust.....

It is unlikely the relay is the problem, its probably the protection circuit doing its job. See above.
 
did you measure the dc offset yet ?
you cant do this at the speaker terminals as the relay is open .


you need the instructions for setting the offset .. this amp looks unfamiliar to me .
 
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did you measure the dc offset yet ?
you cant do this at the speaker terminals as the relay is open .


you need the instructions for setting the offset .. this amp looks unfamiliar to me .

Are you my echo are you Pete....

Yeas the DC offset procedure is a long and tedious road with this amp....

Its a floating bridge design amp.....
 
Are you my echo are you Pete....

Yeas the DC offset procedure is a long and tedious road with this amp....

Its a floating bridge design amp.....

no i just take longer to type and i had to read the manual . never come across this design and not sure if i want to see one on my bench ,:D
that reminds me must get back in there soon to the bench .have had a long break .
 
no i just take longer to type and i had to read the manual . never come across this design and not sure if i want to see one on my bench ,:D
that reminds me must get back in there soon to the bench .have had a long break .

They can be a bit of a handful actually.....not the easiest to work on and diagnose...
They are however an excellent sounding amp, but poorly constructed, lots of plastic and self tapping screws which easily strip......got to be careful with them....
 
Do you have the service manual, for the schematic, and for the offset (and bias) adjustment procedure? - if you don't, get a copy because you will need it for this amplifier.

For your problem you will need to find the place on the main amplifier PCB where you can measure the DC offset BEFORE the speaker relay. DO NOT try to find this spot on the protection PCB itself as there is mains voltage present on that board, (soft start circuitry) and that board is also difficult to access.

See if you can find that spot on the schematic - I do not have the schematic in front of me at present, but you could trace backwards from the speaker relay contacts to the main amp pcb to find this spot. Which, if you are lucky will be sitting at up to 2.5V (should be less than 0.5V and ideally '0'V) - in which case you have adjustments to make. If you are unlucky you have a fault, and the voltage will be higher and not possible to adjust.

Note that BOTH channels DC offset needs to be below about 0.5V to allow the protection circuitry to close the speaker relay contacts.

I will update this post later if I can access a schematic (at work at present) or later this evening when I am at home.

Difficult to work on, annoying flimsy construction not well suited to 'servicing' work, but oh boy, wait till you hear it :music:
 
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LOL nice one Pete :thmbsp: - sadly, the 'industrial strength' work firewall denies me access :tears:

i could have told you a work around but i don't know your work system .
is it just pdf files it doesn't allow ? or particular url.s ?
 
i could have told you a work around but i don't know your work system .
is it just pdf files it doesn't allow ? or particular url.s ?

Seems to be mainly URL's, however - I work for a large company who regard online security as their number 1 priority, thus there is a lot 'out there' that doesn't exist when I am here :)
 
If you look at the first picture in my thread (link above), you will see four inductors on the main board. These are a good place to check DC offsets, when I did mine, I brought these four outputs out to an old breadboard so all the test points were in one place. Remember, this is a bridged design amplifier (sort of), so for each channel there are two offsets to check (hot and cold) before checking the hot/cold balance (could this be called the "warm" balance? :) )

All will become clear when you read the service manual.

Lee.

PS. Now you guys have got my juices flowing, because I have another one of these amps waiting to be fixed. But I have so many other projects on the go, I probably won't get to it any time soon.
 
So you need to check the DC offset between pins 28 & 29 (Left channel) and 31 & 32 (Right channel) on the F-4296 PCB.

I strongly recommend you use 'mini-grabbers' to connect to these 2 points, otherwise you risk shorting something - this would be very very bad. :yes:

This is effectively the Hot/Cold Balance adjustment which should bring the amplifier out of protection mode by adjusting kVR1 (on the F-4266 PCB), and kVR1 (on the F-4267 PCB). Be warned, as stock, these trimmers will be very very sensitive to adjust.

Did I mention that shorting something out while checking the DC offset should be avoided at all costs? :yes:
 
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Thanks for all the responses everyone! I'll get to work on that biasing. I have the manual and schematic. I'll let you all know how it turns out.
 
Well what do you know? It worked. It really is tricky. I've tried biasing it before, but I always gave up because I assumed there was something wrong elsewhere. Those trimmer pots are so difficult to adjust accurately.
Anyway, I got it out of protection mode and it plays music. For future reference, if anyone else can't measure at the speaker terminals due to the relays, I used those resistors right next to the inductors to measure voltage. R76 and R77.

However, I don't think I'm getting the bias right with the output transistors. From emitter to emitter I can only measure a little less than a volt. Per the manual, it should be at 20V. Also, the transistors are very hot. Not quite tube hot, but enough to worry me. Is it probable that the trimmer pots on the f-4296 power amp board are not working correctly? Or could there be some other problem?
 
Silly me, it should be 20mv across those emitters, not 20v. Duh.

Still, they are very hot.
 
Silly me, it should be 20mv across those emitters, not 20v. Duh.

Still, they are very hot.

Do not confuse 'Bias' and 'DC offset' - there are 4 trimmers on the F-4296 PCB for bias. If the output transistors run 'hot' then you are setting the bias incorrectly. If this is allowed to continue you will damage the output transistors. Check and double check how you are setting the bias - very clear in the SM (IIRC - I will double check this and clarify if needed).

The DC offset trimmers are on 3 other PCB's - the main ones being on the F-4266 & F-4267 PCB's.
 
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I think there might actually be something wrong that is affecting these adjustments.
I'm pretty sure my process is correct, I'm following the manual's steps perfectly. Here's what I'm doing.
First I make the adjustments on f-4266 and f-4267. Left channel, then right channel, just like page 14 of the manual. However, when I start adjusting Bias on f-4296, the DC offset is affected and by the time I do the second or third transistor, the protection kicks back in because the offset has changed so much.
Basically, I can get the offset good or the bias, but not both. If those bias pots aren't turned most of the way up, I can't even get the offset low enough to get out of protection.
Additionally I think the bias and offset are drifting when I'm not even touching the pots. What could be causing this? Are the pots faulty? Is this the reason you changed them on yours, leesonic?
 
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