Sansui Au-5900 recap mistake

Mico

Well-Known Member
I made a mistake ordering caps for Au-5900 recap, I took values from PCB and it is beyond me how I overlooked value on quite a big caps. I ordered C11, C12, C23, C24, C607 and C610 at 120mF/50V instead of correct 100mF/50V so I am about 20% higher. Could someone familiar with this amp tell me if I can continue with replacement without risk of blowing the thing or I should give up and get the right value? Reading the schematics is not my strongest point, they are scattered across amplifier/power supply/protection board.
 
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Do you have a cap tester - chances are the replacements may actually measure somewhere between 100-120uF anyway.

I wouldn't have thought that a difference of this small amount would cause any issues - others may disagree.
 
Do you have a cap tester - chances are the replacements may actually measure somewhere between 100-120uF anyway.

I wouldn't have thought that a difference of this small amount would cause any issues - others may disagree.

No I do not have a cap tester, might actually go and buy one now. Caps are Panasonic FC, what bothers me is they might measure 120-140mF as well and that would be almost 40% more.
 
I did not hear Sansui gurus screaming NO! so I assume it would be safe to proceed.
However, if you see a cloud of black smoke coming form the North....
 
I did not hear Sansui gurus screaming NO! so I assume it would be safe to proceed.
However, if you see a cloud of black smoke coming form the North....

Yes, they are all fine, and as Pete says an upgrade which in this case for the positions indicated, is a good thing.
 
Yes, they are all fine, and as Pete says an upgrade which in this case for the positions indicated, is a good thing.

Finally finished recap (big filters, PS, amplifier, protection circuit) except for pre amplifier section and hooked AU-5900 for the first time through DBT. Passed the test fine , no smoke - but also no relay click!?
I went over all caps to check polarity and no mistakes there, what the heck? In the process I also replaced R31,32,41 and 42 fuse resistors with 220ohm/1,4w metal films.Other than having those above mentioned 120mF caps instead of 100mF in 6 places can not figure out what is going on. Also I can not read any idle current across measuring points, is that normal?
 
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I've read the 2SA798 in these can cause problems with the relay. One fix suggested is to take two matched KSA992's and tying the emitters together and inserting it where the 2SA798 was. Just a suggestion as I've never done this myself.
 
need to see some voltage readings starting with the power supply . if that aint right stuff wont work properly .
also what is the history of this unit ? like did it ever work properly for you ? all i see is you changed a few capacitors but never said why .
 
need to see some voltage readings starting with the power supply . if that aint right stuff wont work properly .
also what is the history of this unit ? like did it ever work properly for you ? all i see is you changed a few capacitors but never said why .

Au-5900 was perfectly functional unit in great shape and a friend asked for recap. I replaced all electrolytic caps (including big filters) except preamp boards, stopped there because of this issue.
Also replaced 4 fuse resistors although originals were 100% within specs.
This is not my first, I am not EE I did about two dozen full recaps without one single incident. Above mentioned 120mF/50v have been installed instead of original 100mF/50V
and I am wondering if those might be messing up with protection circuit and relay?
Regarding 2SA798 -KSA992 , I have seen that mentioned before but can not see a reason why it would stop working properly after recap. Might try it anyway.
 
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c607 c610 . all i can see here is regulated voltages coming up may be a little slower . best first check those voltages before blaming the caps ..tr604 emitter -44.5v ...tr605 emitter 42v .
will check the others again now . in case something was overlooked .
 
Will do, took the board out again to look one more time. Do not want to fry anything now, so "+" VTM pin on tr emitter, other on base ?
Hate to do it in the circuit....
 
black lead to shiny chassis .red to test point .
look at the schematic and you should see resistors connected to the emitters . best check there . less chance of causing a short that way . or any other convenient point along the line
 
Happy ending: I plugged Sansui in the wall for the first time without touching anything else and WOILA! relay engaged!
This is kind of weird, I was running it all the time through DBT and any other unit would normally work like that.
I had this possibility at the back of my mind, although it did not make much sense. And I still do not get it.
Have a ruin of AU-7900 in the line for recap and it works through DBT without any issues...
Thanks Pete :)
 
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