Akai AA-1150 Clicking noise

need to figure out why preamp left is not amplifying .maybe shorted transistor .or more likely loss of collector current . just guessing .
 
well..got back to the AA-1135 after the last time i powered it ON without performing bias adjustment.

i checked both output transistors, and only the NPN was damaged. (i check the complimentary PNP and it was fine)
so i installed new NPN, and powered ON, the DBT bright almost fully.
i connected the DMM, and see about 0.6VDC...trying to adjust with the varistor, and it doesn't affect the voltage.
relay doesn't click in (is it matters at all?)

before power ON the receiver i checked that the DMM probes has good contact, and i measued 1.1ohm across bias test points (two Emitters), and also i compared it with the other channel and got same value. (i was afraid something else went bad during the last time i powered on without adjusting the bias).

just to remind you...last time i was replaced:
4 diodes of rectifier bridge (the new ones are 3A, instead of 2A original).
2 outpout transistors...much "stronger" then originals...i put 2SC5200, 2SA1943.
remind you that 2sc5200 transistor become shorted, smoke was out the cement resistor.
and the main fuse didn't blow for some reason!
btw the DBT bulb is 60W at 230vac country. (i guess it's fine...im using it with all other receivers)
(full story at message #71)

why is the varistor doesn't affect the voltage across the transistors? (maybe the reason is that the relay didn't click and i need to handle this first?)
if so...what should i check first in order to find the reason it doesn't click? assuming the high current last time damage other components "on the way"

big thanks..
 
you really need to test all transistors and resistors with power off . you can compare good and bad channel .
 
On board?

How to test? By comparing resistance between equivalent transistors while on board?

You thing i should check resistors also or only transistors?

Thanks
 
Can you just tell me please...
What is the reason the voltage didnt changed while i adjusted the varistor?

Because the relay didnt clicked in? Or it should affect anyway?

I was wondering that maybe the bulb was bright because the transisotr bias isnt correct.. But.. I cant change it because to varistor isnt make a change.
 
relay is not clicking because of the fault .
check transistors like you would normally using diode test and comparing to good channel if readings are off .
check resistors the same way .
 
Alright, will do as you said.

Just to be sure... Varistor dosent make a change because the relay isnt click?
 
Keep going...

I disconnnect the output transistor 2sa1943 and turned ON with DBT.
Relay clicked in.
The transistor itself tested out of circuit and is good.
After put it back on circuit, relay didnt click and bulb was shine.

Is it reduce my options?
I tried to compared left/tight and dodnt find anything different yet.

The complimebtary 2sc5200 just inatalled new one the last time after i shorted it while turned on without performing the bias.

Hope now is smaller options.

Thanks
 
did you replace both output transistors ?
thing is one might be short but the other might be damaged and not show on your meter as being damaged . same with the drivers etc .
 
Really?!?!
I never heared about it (sure i believe you)
If i know of course i would replace both of them.

You mean i will perform the 6 steps diode checks, everything will be fine, and still the transistor is damaged?

Alright.. I will replace it also.
Thanks
did you replace both output transistors ?
thing is one might be short but the other might be damaged and not show on your meter as being damaged . same with the drivers etc .
 
I also have transistor tested.
Too bad i didnt use it.. Was lazy... Only used the DMM.

Do you think its reliable enough to thrust this tester?


Btw, should i concentrate only on transistors?aybe elct. caps or resistors? (I didnt see any diodes on the channels themself.. Only protection circuit..which we already seemsit worked fine with only one channel..

Here is the trans. tester
Screenshot_2019-02-04-00-58-13.png
 
tester will find definite shorts . it wont apply same current as in a circuit . i suspect it because the other one went short .
try a good pair of outputs if no go then remove them . if this is the case i will look at some voltage tests to narrow things down . may need 2 1k resistors to do this .
 
took you back to the AA-1150.
the receiver is working really fine..so lately i'm just playing music thru it (full mains) and wait for the click noise.
after about 1.5 hours (approx 25% volume), it clicked in and out one time (fast) and then keep working regularly...

i remembering you the last time you told me check the relay transistor.
the problem is i can't predict the moment it happens and i'll probably miss it.

so...as you said..maybe rebuild the protection circuit...(11 transistors).
what have you recommend me?

maybe start by replace only the one you circled (relay transistor), or go with all of them?
and..just wondering.. maybe recap the board might help rather then replacing transistors?
btw, you think it might related to one channel (left, right or both) or maybe to the other "single/common" circuits which is not related to specific channel (meaning protection or p.s circuits).. since the power amp board contains also the protection and p.s circuits.

hope this has worked .. i circled roughly the protect circuit . i also circled the relay driver transistor . check its base voltage whilst the relay clicks on and off and when its steady .
index.php
 
@petehall347
Hi
Do you think if i use a cooling spray on transistors in protection circuit while the relay is clicking may help me find the faulty one?

I notice that it happens after i play music for one hour or more...
 
@petehall347

last night i was playing music thru the AA-1150 and after about an hour the click noises started to happen.
i keep it turned ON and let it happen for about 3-5 minutes more, hoping maybe the related transistor may be totally death and it would be easier to track it. (later for the other 2-3 time i turned it ON, the click started to happen really fast...about a minute)

the morning after i noticed an old comment from you (6 years ago) for some guy with same issue. i was so glad, so i run to the store to buy the substitute 2sd667. he find the culprit is the relay transistor (as you already told me last time).
http://audiokarma.org/forums/index.php?threads/replacement-for-2sd571.448936/

i took the old one out, and tested it, it was really fine! (with DMM and transistor tester)
i thought to give the new one a try anyway.
i turned it ON thru DBT, the relay clicked in, but after few seconds the click noises happen again! :(

i'm really...disappointed! but still willing to find the faulty one!
 
well...

really too soon to tell (after about 30 minutes of disappointment).
i thought the only suspect for me now is the relay itself!!
actually i was suspect it from first place... but because it was just thinking..and you are the one that really experienced and has the knowledge.. i thought of transistors (no blame of course...only thanks and praise for you @petehall347 )

so..i thought its the time of using the advantage of an old Youtube i saw about cleaning relays... (maybe 1.5 years ago..)
i cleaned it with deoxit and after with I.P.A alcohol.
i dried it with hair dryer...and..perfect!!! (until now for the last 20 minutes).

it also got rid of the -40mv on the Left channel it had. (now -25mv)
also got rid of the mis-balance in volume it had. (volume & balance and all other potentiometers are already deoxit like new so i knew it's not them..)
and also when the volume knob was all the way down..i also could hear a quiet music from the radio (didnt check with aux/phono)... this also dissapeared!

seems like the relay contacts has a lot of affect!

@petehall347 huge thanks for you! and for all your efforts and patient and willing to help!
thanks a lot!


(hopefully i wasn't happy too early...)
now i left with the AA-1135 to solve...
bought today also the differential transistors for him...maybe it will solve the shorted right channel!
will update...
 
Last edited:
well...i changed the differential transistors in the shorted channel on the AA-1135, and now it works good!
(was strange that thru DMM 6way diode test, them tested to be good. also by the transistor tester they found to be good. the only thing make me suspect them is one of them had very low hFE comparing to the other. but still it was shorted)

now, i just had last issue with the 1135.
it's tuner reception is extremely poor.
any chance recap the tuner section will solve the issue? (or other electrical component?)
or maybe it will be solve only by tuner adjustment?

thanks
 
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