AU-6900 repair and on going mystery.
Single family owned Sansui AU-6900. Was working great until recently, it would not come out of protection or if it did, it would play for a minute then the sound would crackle on the right channel then cut out.
I downloaded the manual and searched the internet for fixes. Here's what I've done so far. Replaced all of the VD1212 with series pair of 1N4148 diodes and replace the 220ohm fuze resistors on the AMP board with 220ohm metal film resistors as recommended by the repair community. I also started replacing most of the capacitors with new parts (40yo AMP). Took out the old relay and cleaned it.
It now comes out of protection from a cold start but after maybe around 8 minutes the right channel would start to get noisy and the relay would quit. It is either going into protection or the relay is bad and goes out after warming up. It would then not start up until its cold.
I have more parts on order to complete the full re-capacitor of the AMP board and the main board. Replacement for the relay. I also found one of the pair of 3.3K ohm 2W resistors (reading 4K) on the power supplies was out of value and will be replaced.
I'm hoping its the relay going bad. Readings at the relay while its on is 24.4VDC so its pretty spot on. Any other suggestions before I spend many hours in the schematics?
Single family owned Sansui AU-6900. Was working great until recently, it would not come out of protection or if it did, it would play for a minute then the sound would crackle on the right channel then cut out.
I downloaded the manual and searched the internet for fixes. Here's what I've done so far. Replaced all of the VD1212 with series pair of 1N4148 diodes and replace the 220ohm fuze resistors on the AMP board with 220ohm metal film resistors as recommended by the repair community. I also started replacing most of the capacitors with new parts (40yo AMP). Took out the old relay and cleaned it.
It now comes out of protection from a cold start but after maybe around 8 minutes the right channel would start to get noisy and the relay would quit. It is either going into protection or the relay is bad and goes out after warming up. It would then not start up until its cold.
I have more parts on order to complete the full re-capacitor of the AMP board and the main board. Replacement for the relay. I also found one of the pair of 3.3K ohm 2W resistors (reading 4K) on the power supplies was out of value and will be replaced.
I'm hoping its the relay going bad. Readings at the relay while its on is 24.4VDC so its pretty spot on. Any other suggestions before I spend many hours in the schematics?
It would be helpful to know what is happening after 8 mins or however long it takes for things to warm up and go pear-shaped. How about measuring any DC on the output, before the relay, so you can see what caused the protection relay to drop out, as it should when there is a DC problem in the amplifier.
Sansui AU-6900 Manual - Integrated Stereo Amplifier - HiFi Engine
This could easily be a semi that has developed a short but with 4 pairs of parallel output devices, it may not be straightforward checking which, if any of these, may be a cause. Otherwise, its a very simple design with basic VI limiters and and DC sensing for protection.
Sansui AU-6900 Manual - Integrated Stereo Amplifier - HiFi Engine
This could easily be a semi that has developed a short but with 4 pairs of parallel output devices, it may not be straightforward checking which, if any of these, may be a cause. Otherwise, its a very simple design with basic VI limiters and and DC sensing for protection.
The original resistors at R612 and R613 on the Amp board are 2W carbon resistors running at 3.3K ohm. One of themwent out of value testing high reading 4k ohm and still tests high when removed. I purchased a new pair of 3.3k ohm 2W resistors which I though were suitable, I tried it and it gets very hot. The originals are monster sized compared to these:
SPR2CT521R332J KOA Speer | Mouser
Any suggestions for a suitable replacement?
SPR2CT521R332J KOA Speer | Mouser
Any suggestions for a suitable replacement?
I think it maybe ok, introducing the new resistor in the power path may have exposed a possible weak part, it was going into protection right away and likely burned it out. I'm now getting no amplifier output, bad, but it is also going out of protection and the part is running fine.
will now have to follow the power amp troubleshooting guide. out of value resistor @4k may have just been masking the he real problem a possible bad tiny transistor.
Unnecessary, there's only one hFE range available, and they are all generally quite closely matched already.
But most small signal transistors in this amp (and most others) can be replaced with KSA992 / KSC1845.
In my recap I missed a bi-polar electrolytic capacitor and had a polar in place. Replaced with same value bi-polar and now comes out of protection and plays audio. Current bias adjusted to 18mv as recommended in service manual. After a few minutes of play right channel starts to have noise and pop.
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Noise pop and and eventually protection relay turns off.
Replaced relay RL601 and transistor TR603, still same. Starting cold it sounds fine, after it warms up the right starts to have noise even with volume all the way to 0. It then will have noise then it goes into protection. I measured DC output on right channel it was jumping around but would average 130mv or so. Not sure how high it got when it pops and protection relay goes off. Looks like I'll now have to chase transistor gremlins starting with IC01 and IC02.
Replaced relay RL601 and transistor TR603, still same. Starting cold it sounds fine, after it warms up the right starts to have noise even with volume all the way to 0. It then will have noise then it goes into protection. I measured DC output on right channel it was jumping around but would average 130mv or so. Not sure how high it got when it pops and protection relay goes off. Looks like I'll now have to chase transistor gremlins starting with IC01 and IC02.
She's alive!!! But there are new issues from possible partial TR replacements in the Equalizer Amp.
All of the replacements below upto March 1st was completed. On first power up there was some noise but the noise stopped as the parts broke in. Waited ~3 minutes then adjusted bias to 18mV per SM. No noise and all good. Played it for about 30-40 minutes at moderate volume 1/3 on the knob then it broke out into noise. At first I thought it was the Power Amp again but no it was not.
At this point, here is what I know so far, the Power Amp is mostly done and clean, no more protection issues and also sounds great. The issue I think now lies with noise coming from Equalizer Amp. I ran the system removing the EQ Amp input to the tone control board, tone control to Power Amp still in place and there was no noise. I also ran the Power Amp section with audio input into "Main In," Power Amp switch set to "separated" and the audio was clean. With the EQ Amp connected there is noise on power up. Here are the detail of the replacements to date.
####### March 1, 2015 #######
Main Caps C701,702 > replaced Nichicon 0.02F 50V Gold Tune
Power Amp and the substitutions:
All Electrolytic Capacitors > replaced with same capacitance some with high voltage and temp ratings and audio grade
VD1212 D01,02,609,612 > replaced series 1N4148
D613 > replaced
Relay RL601 > replaced MY2-DC24
Fuse Resistors R31,32,41,42 > replaced 200 ohm 0.5w Metal Film
out of value R612,613 > replaced 3.3K ohm 2w Carbon Film
All Small Transistors > replaced see below
IC01,02 SA798 > KSA992FBU four matched and each pair thermally bonded
TR01,02,13,14 2SA917 > KSA916YTA
TR03,04,11,12 2SC1951 > ZTX694B (KSC2316YTA on order)
TR05,06 2SC711 > KSC1845FTA
TR07,08,601 2SC945 > KSC945CGBU
TR09,10,602 2SA561 > KSA733CGBU
Parts coming in for the Power Amp
TR604 2SB560 > still original, KSA1220AYS on order
TR605 2SD438 > still original, KSA2690AYS on order
VR01,02 470 ohm pot > still original, 72-T93YB-500 500 ohm multi-turn on order
TR03,04,11,12 2SC1951 > running with new ZTX694B, but KSC2316YTA on order
In total $89.89 in parts including the above order. $50 of it were the main caps. This was my Dad's Amp 40 years and go and I want to bring it back so I don't mind spending the $ on sentimental value.
On the Equalizer Amp there was a partial replacement of caps and transistors I had extra parts for.
C18,19,21,25,29,31,35 > replaced with same capacitance some with high voltage and temp ratings and audio grade
TR05,06,15 2SA726 > KSA992FBU
TR07,08,11 2SC1313 > KSC1845FTA
Because of the noise I'm looking to complete capacitor and transistor replacements on the EQ Amp. Here is what's needed:
C05,06 47uF 6.3v > 47uF 25v Nichicon Audio Grade
C15,16 3.3uF 25v BP > 3.3uF 50v Nichicon Audio Grade Bi-Polar/Non-Polar
TR01,02,03,04 2SC1222 > KSC1845FTA?? (tested the old ones each has hFE >700)
TR09 2SB526 > MJE15033G
TR13 2SD356 > MJE15032G*
*Mouser has MJE15033G in stock but MJE15032G is on backorder. I'm looking at 2SA1837/2SC4793 as possible substitutions. Any suggestions?
Suggestions on the source of the noise issue?
All of the replacements below upto March 1st was completed. On first power up there was some noise but the noise stopped as the parts broke in. Waited ~3 minutes then adjusted bias to 18mV per SM. No noise and all good. Played it for about 30-40 minutes at moderate volume 1/3 on the knob then it broke out into noise. At first I thought it was the Power Amp again but no it was not.
At this point, here is what I know so far, the Power Amp is mostly done and clean, no more protection issues and also sounds great. The issue I think now lies with noise coming from Equalizer Amp. I ran the system removing the EQ Amp input to the tone control board, tone control to Power Amp still in place and there was no noise. I also ran the Power Amp section with audio input into "Main In," Power Amp switch set to "separated" and the audio was clean. With the EQ Amp connected there is noise on power up. Here are the detail of the replacements to date.
####### March 1, 2015 #######
Main Caps C701,702 > replaced Nichicon 0.02F 50V Gold Tune
Power Amp and the substitutions:
All Electrolytic Capacitors > replaced with same capacitance some with high voltage and temp ratings and audio grade
VD1212 D01,02,609,612 > replaced series 1N4148
D613 > replaced
Relay RL601 > replaced MY2-DC24
Fuse Resistors R31,32,41,42 > replaced 200 ohm 0.5w Metal Film
out of value R612,613 > replaced 3.3K ohm 2w Carbon Film
All Small Transistors > replaced see below
IC01,02 SA798 > KSA992FBU four matched and each pair thermally bonded
TR01,02,13,14 2SA917 > KSA916YTA
TR03,04,11,12 2SC1951 > ZTX694B (KSC2316YTA on order)
TR05,06 2SC711 > KSC1845FTA
TR07,08,601 2SC945 > KSC945CGBU
TR09,10,602 2SA561 > KSA733CGBU
Parts coming in for the Power Amp
TR604 2SB560 > still original, KSA1220AYS on order
TR605 2SD438 > still original, KSA2690AYS on order
VR01,02 470 ohm pot > still original, 72-T93YB-500 500 ohm multi-turn on order
TR03,04,11,12 2SC1951 > running with new ZTX694B, but KSC2316YTA on order
In total $89.89 in parts including the above order. $50 of it were the main caps. This was my Dad's Amp 40 years and go and I want to bring it back so I don't mind spending the $ on sentimental value.
On the Equalizer Amp there was a partial replacement of caps and transistors I had extra parts for.
C18,19,21,25,29,31,35 > replaced with same capacitance some with high voltage and temp ratings and audio grade
TR05,06,15 2SA726 > KSA992FBU
TR07,08,11 2SC1313 > KSC1845FTA
Because of the noise I'm looking to complete capacitor and transistor replacements on the EQ Amp. Here is what's needed:
C05,06 47uF 6.3v > 47uF 25v Nichicon Audio Grade
C15,16 3.3uF 25v BP > 3.3uF 50v Nichicon Audio Grade Bi-Polar/Non-Polar
TR01,02,03,04 2SC1222 > KSC1845FTA?? (tested the old ones each has hFE >700)
TR09 2SB526 > MJE15033G
TR13 2SD356 > MJE15032G*
*Mouser has MJE15033G in stock but MJE15032G is on backorder. I'm looking at 2SA1837/2SC4793 as possible substitutions. Any suggestions?
Suggestions on the source of the noise issue?
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some pictures to go with the above post
All the old parts replaced
AU-6900 progress by mpitogo, on Flickr
New main Capacitors
AU-6900 progress by mpitogo, on Flickr
Transistor replacements in progress
AU-6900 progress by mpitogo, on Flickr
All the old parts replaced
AU-6900 progress by mpitogo, on FlickrNew main Capacitors
AU-6900 progress by mpitogo, on FlickrTransistor replacements in progress
AU-6900 progress by mpitogo, on Flickr
She lives and now sounds good.
well in this case we take your word for it even though most of us would trust a distortion analyzer first ...
There is not even one chance in a million that a Japanese amplifier will work the same when you replace the TR09 2SB526 > MJE15033G....
the other one with the series of 1N4148 i will not even comment
Except that you are on a disaster root this amplifier will never sound as it was Problem is that it will sound worst than it was not better ...
Sorry for that
well in this case we take your word for it even though most of us would trust a distortion analyzer first ...
There is not even one chance in a million that a Japanese amplifier will work the same when you replace the TR09 2SB526 > MJE15033G....
the other one with the series of 1N4148 i will not even comment
Except that you are on a disaster root this amplifier will never sound as it was Problem is that it will sound worst than it was not better ...
Sorry for that
The MJE transistors replaced regulated supply ripple filters for the tone and filter power supplies. MJE15032G I believe was out of stock at both mouser and digikey. I don't believe there is an audio signal going through it. As for the VD1212 replacement, in the schematics that part looks to be two diodes in series with a 0.8 volt drop for each and is mainly for the protection circuit.
As far as distortion yes to really look at it I have to do some waveform analysis much like a pixel peeper looks at camera output. For me I have 5 other reference systems to compare to and the sources I'm playing both digital with DAC and analog (vinyl) are familiar to me and sounds good for a 40yo piece of electronic equipment with some new parts.
after the initial breakin period for the new parts I will do some A/B critical listening. This was a fun project for me and I have picture of it with me trying to reach for it at the age of 2.5 years old. It has some sentimental value and I'm glad I can enjoy it again.
As far as distortion yes to really look at it I have to do some waveform analysis much like a pixel peeper looks at camera output. For me I have 5 other reference systems to compare to and the sources I'm playing both digital with DAC and analog (vinyl) are familiar to me and sounds good for a 40yo piece of electronic equipment with some new parts.
after the initial breakin period for the new parts I will do some A/B critical listening. This was a fun project for me and I have picture of it with me trying to reach for it at the age of 2.5 years old. It has some sentimental value and I'm glad I can enjoy it again.
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