sajjad amer
Active Member
Thank you I will take them out and check
Sansui AU-X901 Protection Mode
- Thread starter sajjad amer
- Start date
Goldie99 is right, when you have had blown OP transistors the damage can stretch back past driver to pre-drivers and rarely even beyond. As there are difficulties fault finding with the semiconductors in situ, often the only way is to test them while they are removed, this will find most (but not all) failures. But of course correct substitutes, and NO mistakes when re-installing is absolutely essential to avoid more damage or confusing results after changing. You absolutely must be 'word perfect' on this, otherwise - there will be tears before bedtime. 
Last edited:
sajjad amer
Active Member
I'm waiting for delivery of output transistors, probably on Tuesday now due to bank holiday.
Would you suggest checking another component in preparation for installation of new output transistors?
Thank you so much for agreeing to help
Regards
Sajjad
Definitely, for clarity I will list all those to be checked/replaced = kQ51, 53, 55, 57, 59, and kVR51 - if this is VR is open circuit, as it could be if faulty or oxidised it will cause the bias current to be at maximum giving the burning kR66 & kR64 effect. Any semiconductor near the burned parts should be replaced (shown bolded), Watch your transistor pin-outs when re-installing, please list what substitutes you will be using, and for what.
Do you have a DBT ? - (Dim Bulb Tester) this will save components and your sanity - it is very simple to make and I wouldn't be without one when fault finding an amplifier with this kind of fault.
Don't worry about anything on the F-5694 or F-5695 boards for the time being.
Last edited:
sajjad amer
Active Member
I have managed to check Following
KQ 53-- shorted
KQ 55-- TEST OK
KQ 75-- TEST OK
KQ 59-- TEST OK
KVR51 & all other trimmers have been replaced with Bourns 25 turn trimmers, as per your advice in other threads.
I do have DBT with two 60 watt bulbs in parallel, I hope it is acceptable.
The only transistor substitutions I have used so far are on protection circuit.
2sa1115 and 2sc2603 replaced with ksa1015/ksc1815
I inted to replace KQ53 (2SC2705) with KSC2383 (again thank you for this advice in other thread)
Last edited:
sajjad amer
Active Member
I have a silly question to ask, I forgot to take pictures of output transistors before I took them out. I think this is how the transitors should be oriented
With amplifier laid upside down, looking at the heat sink from Left to Right
A1386 C3519 A1386 C3519 ==== C3519 A1386 C3519 A1386
LEFT RIGHT
Can you please confirm if this is right?
Thanks
With amplifier laid upside down, looking at the heat sink from Left to Right
A1386 C3519 A1386 C3519 ==== C3519 A1386 C3519 A1386
LEFT RIGHT
Can you please confirm if this is right?
Thanks
Take a look on page 4 of the Service Manual, look at the second diagram, and refer to the lower parts listing - see items 6 & 7 - from this you should be able to deduce the positioning of the OP transistors.
As a double check look at the diagram on page 15, figure 4-18 - of the power amp board where it indicates the OP transistor 'Q' numbers on the PCB - note that in this diagram you are looking at the component side of the board.
And as a double-double check note that the collector of the NPN transistor will go to the +ve rail - and the collector of the PNP transistor will go to the -ve rail - see page 21 figure 6-5.
Note:
I haven't confirmed the info in your post because I think it would be better for you to learn how you can work these things out for yourself, if you are in any difficulty with my instructions I will help you further on this - just ask.
PS, there are NO silly questions.
Last edited:
sajjad amer
Active Member
Thank you for the guidance, managed to install the outputs correctly. Switched on with DBT (one 60w bulb). Bulb lights up and then goes dim, no smoke, nothing burnt. No component is getting hot at least to my touch.
Using TP 1 and TP 2, Pin 1 and 4 (out/out) adjusted hot/cold trimmer to 00.17 and 00.6 mV DC. Still in protection mode unfortunately.
I tried to measure the bias on middle and lateral leg of out put resistor and there is nothing 0.00mV.
Voltages on all 8 out put transistors against ground as below +/- 0.5v
A1386= -9, -33, -10 ECB
C3519= -9, +38, -10
Where should I look next to sort out this issue.
Thank you
Sajjad
Using TP 1 and TP 2, Pin 1 and 4 (out/out) adjusted hot/cold trimmer to 00.17 and 00.6 mV DC. Still in protection mode unfortunately.
I tried to measure the bias on middle and lateral leg of out put resistor and there is nothing 0.00mV.
Voltages on all 8 out put transistors against ground as below +/- 0.5v
A1386= -9, -33, -10 ECB
C3519= -9, +38, -10
Where should I look next to sort out this issue.
Thank you
Sajjad
That is a really low -ve (negative) rail as compared to the +ve (positive) rail - maybe the blown OP transistor(s) took out one of the rectifiers in the PSU?
The PSU (for the OP transistors) should output +/-35 Volts with respect to chassis ground. (and dependant on the position of the 'speaker impedance' switch on the rear panel).
See if you can check those voltages, they should be roughly equal numerically - even on DBT.
The PSU (for the OP transistors) should output +/-35 Volts with respect to chassis ground. (and dependant on the position of the 'speaker impedance' switch on the rear panel).
See if you can check those voltages, they should be roughly equal numerically - even on DBT.
Last edited:
Agree Kev, Sajjad, you realise you cant measure DC offset at the speaker terminals because the speaker relay hasn't closed.
You must measure on the power amp board - from the 'middle leg' of each OP transistor dual emitter resistor for each channel R68 & R69 - or at the appropriate pins at TP1 or TP2. ( - depending on which channel you are working on)
Can you locate those points?
NB: might have 'fried' (open) emitter resistors? - best check those while you are checking the other stuff Sajjad.
Each resistor should read 0.22Ω or *---0.22Ω---*---0.22Ω----* for each dual resistor - difficult to read on any ordinary multimeter, but if it reads very low resistance the chances are the resistor is OK - check each one on the damaged channel.
You must measure on the power amp board - from the 'middle leg' of each OP transistor dual emitter resistor for each channel R68 & R69 - or at the appropriate pins at TP1 or TP2. ( - depending on which channel you are working on)
Can you locate those points?
NB: might have 'fried' (open) emitter resistors? - best check those while you are checking the other stuff Sajjad.
Each resistor should read 0.22Ω or *---0.22Ω---*---0.22Ω----* for each dual resistor - difficult to read on any ordinary multimeter, but if it reads very low resistance the chances are the resistor is OK - check each one on the damaged channel.
Last edited:
sajjad amer
Active Member
I have checked the DC offset at TP1 and TP2 , Pin 1 and 4, before adjustment the difference was quite a lot, but after adjustment difference is negligible.
sajjad amer
Active Member
You must measure on the power amp board - from the 'middle leg' of each OP transistor dual emitter resistor for each channel R68 & R69 - or at the appropriate pins at TP1 or TP2. ( - depending on which channel you are working on)
Can you locate those points?
Yes, I can, 5 pin plastic port, I used pin 1 and 4, both labeled out/out
NB: might have 'fried' (open) emitter resistors? - best check those while you are checking the other stuff Sajjad.
Each resistor should read 0.22Ω or *---0.22Ω---*---0.22Ω----* for each dual resistor - difficult to read on any ordinary multimeter, but if it reads very low resistance the chances are the resistor is OK - check each one on the damaged channel.
I will check and report back
Can you locate those points?
Yes, I can, 5 pin plastic port, I used pin 1 and 4, both labeled out/out
NB: might have 'fried' (open) emitter resistors? - best check those while you are checking the other stuff Sajjad.
Each resistor should read 0.22Ω or *---0.22Ω---*---0.22Ω----* for each dual resistor - difficult to read on any ordinary multimeter, but if it reads very low resistance the chances are the resistor is OK - check each one on the damaged channel.
I will check and report back
sajjad amer
Active Member
The power supply board is supplying the amp board with Grey and Brown wires, both measure at -38, +38 with respect to chassis ground on single DBT
sajjad amer
Active Member
DC offset on DBT is 00.10 and 00.6mv
Unfortunately it is still in protection. Should I remove the DBT and see what happens. ?
No, check the bias current - this will be a measurement taken across those emitter resistor pairs, with your multimeter set to read mV - instructions for this are in the SM - there are 2 settings per channel for this. ('hot side' bias current and 'cold side' bias current).
The reason for checking the bias is obviously to make sure it is set correctly, but also too much bias current could be the very reason why protection is still engaged. Too much bias current will cause more voltage to be dropped across the DBT bulb, thus lowering the available voltage to the protection circuit, thus possibly preventing it from disengaging.
Please do not remove the DBT until we can be sure that both channels respond correctly to DC offset and bias adjustment.
When we have verified this we will check what is preventing protection from disengaging.
Last edited: