Aha ! - nice
Please check kR60, kR62, kR76, kR78, and if not already checked kR64 & kR66 - lift one end of each to check.
Report and/or replace any that are faulty.
Sansui AU-X901 Protection Mode
- Thread starter sajjad amer
- Start date
Aha ! - nice
Please check kR60, kR62, kR76, kR78, and if not already checked kR64 & kR66 - lift one end of each to check.
Report and/or replace any that are faulty.
sajjad amer
Active Member
As always you are spot on sir, R62 was open, I have replaced it with 100 ohm resistor and now I can adjust the bias and it's set to 16mv across all 4 output resistors.
DC off set is 00.23 R and 00.19 L
I have not touched KVR 2 at all, what's it's function?
What should I do next?
Thank you
Ok, that's good news!
kVR2 in each channel is to set the 'Cold to Ground' DC offset - my experience is that it is almost impossible to achieve anything like the setting accuracy claimed or required by the SM procedure. So I just set it as accurately as possible and leave it at that, it wanders all over the place and could be 1 or 200mV as set. It has no effect on the ability of the amplifier to come out of protection mode and doesn't seem to affect anything else as far as my investigations have shown.
So at the moment the bias has been set with the amplifier powered via DBT, if you were to connect it to full mains now you could cause some damage - because the bias will obviously be set for a lower supply voltage overall, thus making the full mains bias far too much.
So, the next thing to do is to turn down the bias.
What I do here is to turn the bias down so that 'just a sniff' is visible on the multimeter i.e. between 0 and 5mV. - note again - this is FOUR adjustments.
Let me know when you have done that.
kVR2 in each channel is to set the 'Cold to Ground' DC offset - my experience is that it is almost impossible to achieve anything like the setting accuracy claimed or required by the SM procedure. So I just set it as accurately as possible and leave it at that, it wanders all over the place and could be 1 or 200mV as set. It has no effect on the ability of the amplifier to come out of protection mode and doesn't seem to affect anything else as far as my investigations have shown.
So at the moment the bias has been set with the amplifier powered via DBT, if you were to connect it to full mains now you could cause some damage - because the bias will obviously be set for a lower supply voltage overall, thus making the full mains bias far too much.
So, the next thing to do is to turn down the bias.
What I do here is to turn the bias down so that 'just a sniff' is visible on the multimeter i.e. between 0 and 5mV. - note again - this is FOUR adjustments.
Let me know when you have done that.
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sajjad amer
Active Member
Thank you, I have reduced bias to 5mv on all 4 output resistors
OK - well, I am going to take a guess that there is nothing wrong with the protection circuit, and that it will operate normally when connected to full mains.
Please disconnect any speakers, volume to minimum, no inputs connected.
So, please connect the amplifier to full mains - and we'll see what we get.
Please disconnect any speakers, volume to minimum, no inputs connected.
So, please connect the amplifier to full mains - and we'll see what we get.
sajjad amer
Active Member
Done as suggested, Still the orange protection light is blinking I am afraid. DC offset is 00.19 L and 00.10 ROK - well, I am going to take a guess that there is nothing wrong with the protection circuit, and that it will operate normally when connected to full mains.
Please disconnect any speakers, volume to minimum, no inputs connected.
So, please connect the amplifier to full mains - and we'll see what we get.
Is this 0.19V L (or 190mV) and 0.1V R (or 100mV) ? - and where are you measuring - from the centre point of one dual emitter resistor kR68 (red probe) to centre point of the other dual emitter resistor for that channel also called kR68 (black probe) ? anywhere else may be the wrong place - especially at the speaker terminals = wrong.
Once again a warning about probes - be careful.
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sajjad amer
Active Member
I am measuring at TP1, Pin 1 and 4. It is mV.
measuring between the centre point of dual emitter and ground on each side it is -1.7mV
Are you able to adjust that at all? - just so we can be sure you are in fact monitoring DC offset.
These are very low readings - possible - but nevertheless outstandingly low - so I am suspicious.
Also the instruction to do this was wrong. TP1 pins 1 & 4 are correct, or the centre of emitter resistors as described above. (not centre of emitter resistor to chassis)
sajjad amer
Active Member
Yes, I can adjust the dc offset using KVR1 (hot-cold) on both Right and left side. I can take it right down to 00.00 mV but my hands are not that good, it just shifts to +/- 00.50mV.
sajjad amer
Active Member
Just to double check that
Volume is minimum
tone controls, zero
speaker A button "on"
Power Amp Direct is set to "normal"
Source Direct Button is set to "on"
CD selected as source.
I hope this is how I should be attempting settings.
Thank you
Volume is minimum
tone controls, zero
speaker A button "on"
Power Amp Direct is set to "normal"
Source Direct Button is set to "on"
CD selected as source.
I hope this is how I should be attempting settings.
Thank you
Just to check a few things:-
If you alter the speaker select switches - can you hear relays clicking at the rear of the unit?
You still have the flashing protector light ?
Do you have headphone output? - plug in headphones if you have any? - connect a cd player or something and see if you have output.
It is possible you will have speaker output as well ! - but with a flashing protection light.
If you alter the speaker select switches - can you hear relays clicking at the rear of the unit?
You still have the flashing protector light ?
Do you have headphone output? - plug in headphones if you have any? - connect a cd player or something and see if you have output.
It is possible you will have speaker output as well ! - but with a flashing protection light.
sajjad amer
Active Member
Just to check a few things:-
If you alter the speaker select switches - can you hear relays clicking at the rear of the unit?
You still have the flashing protector light ?
Do you have headphone output? - plug in headphones if you have any? - connect a cd player or something and see if you have output.
It is possible you will have speaker output as well ! - but with a flashing protection light.
- changing speaker select switches I do not hear any relay click.
- I still have flashing protector light
- I have connected CD player, there is no out put at headphone jack.
sajjad amer
Active Member
Yes, I did change them as Q31 was physically broken and I could see the innards of transistor.Please see post no 9, it has a picture of broken transistor.
Thank you
sajjad amer
Active Member
The substitutes on the protection board are from Digikey , however I do have the "original" or "original looking" transistors from China as well, shall I replace them in protection board ? Their hFE matches the original ones.
Just a thought
Ah yes, I see. - wow.
I assume you checked the pin-outs on the replacements - and took note of the fact that there are 2+1 x NPN and 2+1 x PNP and they have to go back in the right places? - just seen your post above - no, no need to put the originals in - as long as you are sure of the above.
I think we will stop here if that is ok with you, the next bit will be even more difficult and you will have to remove the rear panel to get at the protection board.
I assume you checked the pin-outs on the replacements - and took note of the fact that there are 2+1 x NPN and 2+1 x PNP and they have to go back in the right places? - just seen your post above - no, no need to put the originals in - as long as you are sure of the above.
I think we will stop here if that is ok with you, the next bit will be even more difficult and you will have to remove the rear panel to get at the protection board.
sajjad amer
Active Member
Yes I was careful with the replacements, just to check again pin out of originals and replacement transistors were same.
Yes certainly we will stop and I will wait for your next instruction as and when you like.
Once again I am grateful for your kindness.
Regards
Sajjad
