Akai AA-1150 Clicking noise

rotco

Active Member
Hi all.

i've got this Akai AA-1150, which partly works.
it's play music fine, but suddenly it's stop, and clicking noise being heard.

at the video, the receiver isn't connected to anything except of the power cord. (no inpust, no speakers)
so, you can hear random clicking noises.
any ideas what can it be?

thanks

link to the video:
 
I'd say its the speaker protect relay clicking in.

You need to measure the DC offset at the speaker terminals - you will only get a reading at the times the relay switches the speakers on. Get a DMM and set it to mV and red to red (with the probes) and black to black when connecting to the speaker terminals.

The DC offset is probably borderline too high, causing the relay to click in and out.

The way to fix this - if confirmed by the above - is to download the service manuals and setup the DC offset levels following the process in there.
 
I'd say its the speaker protect relay clicking in.

You need to measure the DC offset at the speaker terminals - you will only get a reading at the times the relay switches the speakers on. Get a DMM and set it to mV and red to red (with the probes) and black to black when connecting to the speaker terminals.

The DC offset is probably borderline too high, causing the relay to click in and out.

The way to fix this - if confirmed by the above - is to download the service manuals and setup the DC offset levels following the process in there.
Thanks for your reply!!
I also think about the speaker rely, because i thought ita the only componnent which can actually move and make a noise of movement!
But, in contrast, i thought if its clicks in and out, i would see the lightning turn off and on also?
What do you think?

Thanks
 
Great! Thanks

So, i haven't tested the voltages yet at the terminals, but, as firat step i tried again but while i set the speaker selector switch to OFF.
Then, the same issue with clicking noises.

Is this test should imply something?
Or maybe the switch is later the relay in the circuit?
 
I mean.
I understood that while doing the dc offset test i need the speaker switch to be selected on the same terminals.

But, i asked, if the fact that the clicking noises appeared also while speaker switch ls OFF if it maybe stands in cotrast to relay click on and off (and from there.. To the exising dc offset)

So, is ot matter or i can ignore this fact?
 
The relay has nothing to do with the speaker switch. It is only for protection. I'm not sure how your exact model works but most protection relays do not make contact for several seconds after the power is applied. This allows to power supply to stabilize and prevent the speakers from thumping. If excessive DC offset is present at the speaker terminal, the relay opens to prevent the speaker from being damaged or even catching fire in the event of a shorted output transistor. I believe it will also open to protect the amp in the event of over current such as too low of impedance or too many speakers... or even speaker wires shorted.

Slimecity is suggesting the DC offset is out of whack causing the protection relay to open. It could also be a fault in the protection circuit. You need to test the offset first to see if there is a problem in either channel.
 
@petehall347
Hi
So i look in the s.m
And confused about the current/voltage.
I measure mV correct?
Do i need to calculate the ampere?
What is the resistance value i need to take into calculation if so?

Thanks
 

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Alright
So I've just got the time to touch it today.
first plug it in, and put the DMM probes on the speakers terminals on the back as you said.
turn it ON, and yeah, iv'e got this click noises coming from the relay, while the reading on the DMM jumped between 25mV to about 100mV.

Then i plug it out of the wall!
touch my probes at the points mentioned in the S.M, while the DMM set to measure resistance, since i wanted to check the resistance there.
somehow (yeah i know it should be care with extreme caution) my hand moved, and i see a small spark.

at next step i plug it with DBT and, unfortunately, the unit now shorts!!
(so sucksss! starting with probably small issue, ending with so complicated one!)

(How come this spark appear?! because charged capacitors on the board?!
alright...if so... are this charge so strong and continual to kill the output transistor?

so...the big issue now..
this transistors are the batwing type, and also the board is really not accessible. (i figured it out only today while looking for substitute here on AK)
gonna be long work for it....
 
Hi again,

i have both AKAI AA-1135, AA-1150 both are SHORTED. both sharing same service manual.
so i thought i could get the help of both of them to maybe understand about the other.
the AA-1150 i accidentally shorted it's output transistor (left channel).
the AA-1135 i bought it shorted already, don't know what is the problem.

i know when unit is shorted, most of the time is the output transistors.
so i start check both of them for shorted pins, and grounding. and this is what i find (explain in the photo - will be much more clear)
** both test was made while power cord out the wall, and while every component still on board (no unsolder yet)

for some reason i suspect that in the 1135 the short is not in the output transistors.
about the 1150, i guess soon ill take both Left channel out, and check if they are really shorted and if while they OFF board, the unit is still shorted.

can you tell me if you can refer anything from my test results?
thanks!!
happy new year everyone

20181228_104933.jpg Untitled.png 20181228_135000.jpg Untitled.png
 
I am very inexperienced and not really knowledgeable but i would
Unsolder the output transistors, one at a time and test on diode mode with your multimeter per mark the fixers instructions on how to check transistors.
Figure out if your outputs are blown before moving ahead.

If your outputs are blown because you shorted them accidentally probing around, that's one thing, but you also sound like you have other issues at play too.
You may well have capacitors that are shorted, or other transistors out of whack.
An inspection of the relay may tell you if it needs replacing.


Hopefully someone will correct anything wrong in what I have suggested.
Either way be very very careful about messing with this stuff, you need a dim bulb tester and drain filter caps before probing around.
 
Hi, updating..

regarding the AA-1150:
I was dismantle both output transistors at left side, and then turn it ON thru DBT (see picture)
receiver plays just fine for 30 minutes i tested. play music on Left channel only, without clicking noise from relay.
i bought 2SC5200 & 2SA1943 (Package case type TO-3P(L)) as substitution, and thought of mount them in diagonal, but i couldn't - too big.
so i go back to store and replace for MJE15033 & MJE15032 (Package case type TO-220) and hope it will solve the issue.
all issue began because of clicking noises in the relay, so i guess after changing the outputs i will need to adjust bias. (carefully not to burn them again).

Regarding the AA-1135:
I couldnt see any clue for output transistors shorted. (except both collectors of 2sd587 (NPN) shorted with ground, which i'm not sure it should be like that).
any ideas?
Also, on it's board i see two transistors (one near the other), both mounted on small heat sink. they seems suspect to me.
on both written BD711. I couldnt see a clue for them in the service manual.

1150 outputs:
20190101_215807.jpg
 
@petehall347
Hi
So i look in the s.m
And confused about the current/voltage.
I measure mV correct?
Do i need to calculate the ampere?
What is the resistance value i need to take into calculation if so?

Thanks

Measure 25mv across the points shown in the pic to set the bias if not 25mv adjust trimmer pots shown in the diagram to achieve this voltage
 
Hi,
thanks @petehall347 , @reddish75 .

so i eventually replace the outputs with 2SC5200 & 2SA1943.
i mounted them upside-down, and used a silpad insulator beneath.
i used one of the original drilled bore.
now the receiver turned ON thru DBT, and lamp dim low (yeahh!)
i tested the speaker terminals on the same channel of the new outputs, and was about 40mV.
next step i will do the bias adjustment.

the work-around i did with mounting these transistors, will be more hard to touch the tested points (since i took the wires directly to the transistors leads, and bypass the small PCB, also now it's "mirror" picture, so need to be very careful not to do mistake where to put the probes)

i wanted to ask your opinion for my work-around.
i soldered the wires directly to the leads, and also use tie-wraps as a mechanical safety in any case the soldering will dis-attach in the future)

20190103_011643.jpg 20190103_011655.jpg
 
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