Hello all,
I humbly beg for some assistance from the diyaudio crew.
I am currently trying to repair a Sansui AU517. It kept blowing the main fuses on the psu PCB. I know that the fuses blew for a reason that's why the replacement fuses were of the 1 Amp variety.
The fault finding so far has been to unplug all PCB power connections and then power unit up to prove the rectifiers and main caps were ok. This went well and no fuses blew and voltages measured correctly at each connector. Then I proceeded to reconnect the PCB power one by one. All ok until I tried to power up the power amp PCB (F2722) on one of the channels.
So now I know that this PCB has a problem. What would be the best way to proceed. I want to respect this amp and not start unsoldering and removing components without thinking things through first.
I'm sure there are other faults but this is a good place to start. I do have the service manual.
Any hints would be very much appreciated.
Many thanks
Paul
I humbly beg for some assistance from the diyaudio crew.
I am currently trying to repair a Sansui AU517. It kept blowing the main fuses on the psu PCB. I know that the fuses blew for a reason that's why the replacement fuses were of the 1 Amp variety.
The fault finding so far has been to unplug all PCB power connections and then power unit up to prove the rectifiers and main caps were ok. This went well and no fuses blew and voltages measured correctly at each connector. Then I proceeded to reconnect the PCB power one by one. All ok until I tried to power up the power amp PCB (F2722) on one of the channels.
So now I know that this PCB has a problem. What would be the best way to proceed. I want to respect this amp and not start unsoldering and removing components without thinking things through first.
I'm sure there are other faults but this is a good place to start. I do have the service manual.
Any hints would be very much appreciated.
Many thanks
Paul
If you have a failed output transistor, you likely have dead driver transistors too. Getting the old parts is quite likely to be difficult or impossible. Forget eBay - you will most likely just get counterfeits.
Onsemi MJ21193/4 should make good replacement output devices. If the driver transistors (TR12 and TR13) are toast, MJE15030/MJE15031 should replace them.
When you power up the unit after replacing the transistors, it is best to insert an incandescent (old style filament) bulb in series with the mains live. This will limit fault current if there is a problem. Also make sure to re-adjust the bias current as shown on page 4 of the service manual.
Onsemi MJ21193/4 should make good replacement output devices. If the driver transistors (TR12 and TR13) are toast, MJE15030/MJE15031 should replace them.
When you power up the unit after replacing the transistors, it is best to insert an incandescent (old style filament) bulb in series with the mains live. This will limit fault current if there is a problem. Also make sure to re-adjust the bias current as shown on page 4 of the service manual.
Replaced the output transistors with MJ15003 / MJ15004 and the driver transistors with MJE15031 / MJE15030 (Yes these were toasted too). Had these left over from making leach amps. The fuses no longer blow. The amp is now just totally silent can't even hear power supply noise in the speakers. The protection circuit seems to be happy enough and switches the output relay on. Wiring between amplifier pcbs and output relay is ok along with relay output pins connecting to the speaker terminals.
Suppose the next thing to do is connect signal generator to amp inputs and check it is getting through to the amplifier PCBs. Then powering up the amplifier PCBs outside of the amp chassis and applying signal generator to their inputs.
I really want this amp to work again as it sounded lovely when it did.
Suppose the next thing to do is connect signal generator to amp inputs and check it is getting through to the amplifier PCBs. Then powering up the amplifier PCBs outside of the amp chassis and applying signal generator to their inputs.
I really want this amp to work again as it sounded lovely when it did.
Update....
Performed testing on input/preamp circuits and test wave form shows up at the connectors feeding the power amp pcbs. However, even on the (maybe undamged) pcb there is no output from the power transistors.
Have taken out damaged pcb and powered it up outside of the amp and applied signal generator to input pcb. Have traced signal through pcb and found that at TR5, TR7 that the signal levels drop off dramatically. At the bases it is strong but at the emitters it is weak. Have done diode tests on these and they don't appear to have been fried. There also doesn't appear to be any bias current.
What next?
Performed testing on input/preamp circuits and test wave form shows up at the connectors feeding the power amp pcbs. However, even on the (maybe undamged) pcb there is no output from the power transistors.
Have taken out damaged pcb and powered it up outside of the amp and applied signal generator to input pcb. Have traced signal through pcb and found that at TR5, TR7 that the signal levels drop off dramatically. At the bases it is strong but at the emitters it is weak. Have done diode tests on these and they don't appear to have been fried. There also doesn't appear to be any bias current.
What next?
One thing to bear in mind is that you have a working channel. You can use this as a reference for DC operating points at various places. If you then see anything wildly different on the non working channel, you know the problem is going to be around there.
My guess would be TR05 or TR07 saturated when the output stage went, and that burnt out the resistors. They may have been fusibles.
My guess would be TR05 or TR07 saturated when the output stage went, and that burnt out the resistors. They may have been fusibles.
Thing is the other channel doesn't seem to be working either. Someone had tried to repair this amp in the past and there is evidence of the protection circuit being partially disabled. I took the other module out and checked these resistors and they were open circuit too.
The amp was working after this repair but sounded weak. Prior to this repair it had been given a damn good thrashing where it cooked a tweeter. This repair was done around 20 years ago (this was before I was bitten by the DIY bug) by a local repair place.
It's all so puzzling as its a dual mono design and wouldn't expect identical faults to occur on both halves. Although only one output transistor has been destroyed.
Further research has suggested they are fusibles and are a common problem.Can I replace them with equivalent value non fusibles. I think they are 150 Ohm.
I have a couple of bench power supplies that have variable current limiting from 10mA upwards. So that may mitigate the risks of removing the fusibles while fault finding.
The amp was working after this repair but sounded weak. Prior to this repair it had been given a damn good thrashing where it cooked a tweeter. This repair was done around 20 years ago (this was before I was bitten by the DIY bug) by a local repair place.
It's all so puzzling as its a dual mono design and wouldn't expect identical faults to occur on both halves. Although only one output transistor has been destroyed.
Further research has suggested they are fusibles and are a common problem.Can I replace them with equivalent value non fusibles. I think they are 150 Ohm.
I have a couple of bench power supplies that have variable current limiting from 10mA upwards. So that may mitigate the risks of removing the fusibles while fault finding.
just a couple of things
together with the things you do you will probably need to recap the all unit ..Your amp is quite old and since you invest time and money on it make sure that will last longer .
I presume that for symmetry reasons you will change all the transistors and working ones also
Finally changes like the above and even though 15003-4 + 15031-32 combos are extremely rugged devices in practice proved to produce far more rough sound next to their Japanese cousins
In your case i would go for 1943 5200 with 13xx 47xx drivers recap the amp add better decoupling take care of input capacitors and filters work with miller caps and so on
Kind regards sakis
together with the things you do you will probably need to recap the all unit ..Your amp is quite old and since you invest time and money on it make sure that will last longer .
I presume that for symmetry reasons you will change all the transistors and working ones also
Finally changes like the above and even though 15003-4 + 15031-32 combos are extremely rugged devices in practice proved to produce far more rough sound next to their Japanese cousins
In your case i would go for 1943 5200 with 13xx 47xx drivers recap the amp add better decoupling take care of input capacitors and filters work with miller caps and so on
Kind regards sakis
I checked a few places and it is recommended to use MJ21193/4 outputs on this amp. I wouldn't like to risk substituting faster devices. Also mounting TO-264 flatpack devices to the heatsinks could be a pain. The MJ15003/4 should be enough to get it to work, though.
I would agree on the electrolytic capacitors, they are probably at the point where they require replacing due to age. It's never good when you get an amp that is "struck by technician" who didnt know what they were doing
The biggest problem you will have is if the input dual FET, the 2SK97 is damaged. They are pretty much unobtainium along with any decent audio quality small signal FETs these days. Fortunately all the other parts can be substituted fairly well.
I would agree on the electrolytic capacitors, they are probably at the point where they require replacing due to age. It's never good when you get an amp that is "struck by technician" who didnt know what they were doing
The biggest problem you will have is if the input dual FET, the 2SK97 is damaged. They are pretty much unobtainium along with any decent audio quality small signal FETs these days. Fortunately all the other parts can be substituted fairly well.
I too noticed that the MJ21193/4 is being suggested as good replacements. Read that oscillation could be a problem with the faster devices. Mounting the different packages would extra work but probably not too difficult as there is plenty of space.
Fortunately, the input fets appear to be ok or at least the input side of them is functioning ok.
I suspect that the abuse this amp sustained weakened some of the devices. Then to have the protection pcb partially disabled just masked the fault(s) rather than fix them. It never sounded right after the initial "repair".
Oh well, next step would be to replace the fusible resistors.
Fortunately, the input fets appear to be ok or at least the input side of them is functioning ok.
I suspect that the abuse this amp sustained weakened some of the devices. Then to have the protection pcb partially disabled just masked the fault(s) rather than fix them. It never sounded right after the initial "repair".
Oh well, next step would be to replace the fusible resistors.
Success!!!!!!! I have a working sansui again. Replaced all the fusibles in both channels and the drivers + outputs in the blown channel and I have sound and pretty good sound as well (given that its driving some coda 7s with a really naff cd player)
Next step, change drivers in other channel and decide what output transistors to use and which electrolytics to replace and what type. Thinking either Panasonic FCs or Rubycon ZAs?
Also, reinstate the protection circuit properly but that will be another day.
Next step, change drivers in other channel and decide what output transistors to use and which electrolytics to replace and what type. Thinking either Panasonic FCs or Rubycon ZAs?
Also, reinstate the protection circuit properly but that will be another day.
Glad to hear you've cracked it well done!
Both of those capacitor types you mention are good quality. I have a slight preference for the Panasonics but that is based on price and availability.
I'd suggest, even if the other channel is working OK with the original parts, to replace the drivers and outputs the same, so that they match.
CPC should have all the parts you need
well done!Both of those capacitor types you mention are good quality. I have a slight preference for the Panasonics but that is based on price and availability.
I'd suggest, even if the other channel is working OK with the original parts, to replace the drivers and outputs the same, so that they match.
CPC should have all the parts you need
Jaycee, thank you for your help. It is much appreciated.
Panasonic FCs are my favourite too for the same reasons. They represent good value for the performance.
Yes will definitely do the changes to the other channel as there is a noticeable difference in sound quality. The modded channel sounds much sweeter even with MJ15003/4.
Farnell is my first choice of supply or RS (but they do not seem to stock the MJ21193/4) as they have a trade counter near by.
It is much appreciated.Panasonic FCs are my favourite too for the same reasons. They represent good value for the performance.
Yes will definitely do the changes to the other channel as there is a noticeable difference in sound quality. The modded channel sounds much sweeter even with MJ15003/4.
Farnell is my first choice of supply or RS (but they do not seem to stock the MJ21193/4) as they have a trade counter near by.
Need some help please....
Well is not an AU517 but is a Sansui 5050
My problem is the protection circuit is always on and I get nothing in the output.
I have checked everything
Removed end measure output transistores and drivers
Changed most of the capacitors on the amp board
Everything measure/tested fine and the DC offset before the relay is only 5mV on each channel.
Tested the protection circuit, replaced capacitors and cant fine anything wrong with it.
The only thing I fine a bit odd is the transformer voltages.
There are 3 different voltages, 1 with 6.3V for the light bulbs in the front panel (Ok)
1 symmetric for the pre/tuner stage (OK)
the last one is symmetric for the power stage and is off, there is a +/-4V difference between rails.
Can this cause the protection circuit to quick in ?
Merry Christmas
Ric
Well is not an AU517 but is a Sansui 5050
My problem is the protection circuit is always on and I get nothing in the output.
I have checked everything
Removed end measure output transistores and drivers
Changed most of the capacitors on the amp board
Everything measure/tested fine and the DC offset before the relay is only 5mV on each channel.
Tested the protection circuit, replaced capacitors and cant fine anything wrong with it.
The only thing I fine a bit odd is the transformer voltages.
There are 3 different voltages, 1 with 6.3V for the light bulbs in the front panel (Ok)
1 symmetric for the pre/tuner stage (OK)
the last one is symmetric for the power stage and is off, there is a +/-4V difference between rails.
Can this cause the protection circuit to quick in ?
Merry Christmas
Ric
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