au-9900 stuck in protection mode

darai22jp

Active Member
Hello.
This is my first post ever, although I am always checking out other threats. Living in Japan I am a fan of old Sansui gear, proud owner of an AU-666 and a AU-7500 both of them brought to life by myself. I have some knowledge but I am not a technician.
I was able to secure an au-9900 which kind of worked... distorted sound, noise from left channel... so I decided to recap it. Took me a couple of days...powered on for the first time and the relay made the nice "click" but suddenly disaster... 2 fuses blew in the relay board (F2582).
After a quick check, realized that a piece of lead from my suction tool was in the middle of the fuse holders contacts and that shorted the board....replaced fuses, powered on and again blown fuses again....so I started to look for damaged components. Found out that D002 in F2582 was shorted and tr06 in F2568 was shorted as well. After replacing those It power on fine but stays in protection mode.
I checked the transistors in f-2583 and also checked the output transistors but they all seemed alright (tested with diode method).
I was wondering if anybody has any experience with this amp. Any pointers would be of great help.
Thank you.
 
Yikes - there are a few issues here.

Firstly, you really want to diagnose and fix a fault with an amp before doing maintenance on it - including recapping. otherwise it makes it harder to ID to fix the original fault - plus you may introduce new problems with your new work.

Second - this is not an easy amp to work on - you will be aware that there are many seperate boards inside the amp, and they are all interconnected - these interconnections can go "wrong" at one end, and the "pass thru's" may need fixing (do a search on this on this forum). I had a 9900 and eventually sold it as I couldnt for the life of me diagnose on intermittent dropping-out channel in the pre section.

Yea the disaster you have detailed has probably meant that a power rail has shorted to ground (in my opinion only), this can cause the rectifier and/or outputs to blow. What function does D0002 have, is this one of the dual rectifier bridge units? If so, what dod you replace this with and where did you get it from?

So your output trannies test OK - is the bridge rectifier totally OK also?

Have you built a DBT? that is a great and simple tool for trouble shooting and safety of the amp.

There are some very experienced experts on this amp who will chip in shortly, hold fire.....
 
Found out that D002 in F2582 was shorted and tr06 in F2568 was shorted as well.

I can't find a 'D002' on the F-2582 PCB - they all start with 'D6xx' - also which 2 fuses blew, your choices are F601, F602, F603 or F604.

Check all the PSU voltages are correct, you should be able to find:
+32 / -33V (regulated)
+65 / -67V (regulated)
+35V (unregulated)
and
+/- 55V (left) and +/-55 (right) (both unregulated)

Please clarify.
 
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Hello
Thank you all for your replies.
Sorry I mess up...is not D002 but D602 my bad. Got replacements from a local shop, the owner, very nice guy is always helping me out sourcing parts.
We just realize we picked the wrong diodes and replaced everything with 10d1s and some are 10d2s so l'll be correcting that tonight.
The voltages
are very appreciated that will help me to diagnose further.
@slimecity : what is the bridge rectifier part you are mentioning?
Thank you
 
UPDATE
Replaced the diodes with correct types (10d1/10d2s) replaced the relay, and tr01-06 just in case and that lovely green lamp popped up!, I am so relieved now but
I can`t say anything until I finish to set bias... any recommendations (things to be careful about) any input will be really appreciated.
Thanks
 
Guys, where are your manners? darai22jp, welcome to AudioKarma. You have joined a long list of members drawn here to get help repairing a classic Sansui amp. When you get a chance, please post the serial number for the database. Click on the link in my signature block.

- Pete
 
Hi.
Thank you for your messages. Finally powered up no smoke, no blwn fuses. Green lamp... now tried to set bias following the repair manual and I cant set it.... is there another way? Thanks
 
2 ways to do it - as per the SM i.e. with your meter (set to current) in line with the power feed to each channel in turn. This won't work if the meter fuse is blown, you must replace the fuse with the exact correct type before proceeding.

OR, your meter set to mV measuring across 1 or 2 emitter resistors for one pair of OP transistors - the mV reading to expect should be in one of the threads linked earlier in this thread (e.g. linked in post #8 here - post #1 step 5 in that thread) - only do this if you have a set of mini-grabber test leads - as with 'probes' the possibility of slipping (and shorting something) while measuring is too high.

NB: if you are using multi-turn (25 turn) bias adjustment pots you will need to turn them quite a lot before you can see a bias reading, and if you are using the originals CHANGE THEM!
 
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oops.. fonud out my meter fuse was blown... replaced... all thumbs up.. but during the adjustment I touch "something else "with the screw driver some sparks....
but everything looks normal.... phew....
Connected speakers.. my ipod... nice sound... BUT I need to turn the volume almost at 11 o`clock (-42) to get normal level of volume... is that normal?
Thanks
 
Hello went over the F-2570 board again...used 2sc1313 -> 2c1845, 2sc1708 -> 2sc2240,
2sa798 -> tried with 2sa970 and 2sa1015 paired by the emitter with shrinking tube....no sound still...went through connectors board...nothing
cables everything ok...deoxit same story.....I am tired and about to quit in this amp....any help would be really appreciated.
thank you
 
You aren't going to get anywhere by rhythmically changing transistors (if that's what you were doing?), - you need to trace the signal path and find out where it is lost. Have you made sure the F-2570 board has +/- supply voltages? - the AU-9900 has complex input switching, but you should be able to use a multimeter (set to ohms) to check for input continuity - firstly from the phono input sockets to the F-2570 PCB - if that is OK - then you have an electronic problem with the F-2570 or an output switching issue from the F2570 onward - a problem which can be attacked in the same way.

Obviously if you have an oscilloscope and a signal generator this might be easier, providing you know how to use them.

Don't give up you are nearly there!
 
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There is rarely a problem in the phono preamp and almost never the loss of both channels! Both channels out usually means power supply or ground or something disconnected or not connected properly. There is a screw behind the front panel that completes the ground path to some of the circuits in the amp and I think the phono preamp is one of them! If the screw gets loose or is missing you get no audio in the affected circuits. Re-read my post for the fix for this.
 
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