issue with AKAI AA-1030 Receiver

[rotco]

back to the rx.
i gave it another cleaning...really deep one... deoxit everything.. especially the selector switch which was felt to me a bit "sticky", and the volume knob which felt to me like "Lack of continuity".
(btw, when i encounter a really dirty one and sticky, i give it a heat with a hair dryer fan, and after that i deoxit it. it turned to be really effective).
i let it 24h to dry since i use oily deoxit with lubricant.

from first operation (it was late at night i couldn't really go deep into what you recommend me yet... just turned it on to see if the cleaning helped).

and i feel like the explosion noises got really less worse, only when i got about around +80% of the volume... (before i thing it happens already in 40%).
but, what i realize now is... that it might just not amplifying!
try to say... that i turned the volume up to approx. 80%... and the speakers makes only a low volume..
so.. might it means that there is an issue with the Power Amp level? and the only reason i still got music thru the speakers its because of the Pre amp board? (i used i really cheap headphones also... they were felt like they having the same behavior as the speakers)

if so.. how can i continue from here?
@mbz - i checked if the bass frequency has a special effect.. and it didn't feel like that. plus, i tried to "play" with mono/loudness switches... also, no special effect.

for the fuses i said they are in parallel. sure i was wrong! just wrote it and i knew i was wrong.. they are just lying one parallel to the other.

for the Scope... i don't really need lots of room on my desk... i'm using a laptop.
do i really need to do all this precautions? the device itself hasn't have the protective components in it? do i really need to make a DIY protection?
what's the connection to my sound card?
the Scope is only connected thru USB.
(it's only a hobby... i really don't want to but a scope higher then 60 bucks...as long as i can purchase this one with reasonable price)

from the computer (or actually my cellphone) i hoped to insert the audio signal from a basic free "signal generator" app.

p.s
thru this quick basic operations.. i notice also that the high frequency filter switch isn't reacting at all. (the low frequency filter did it's job..
i guess it cannot affect now.. and i will deal with it later after the receiver will back to life... hope so
(maybe it's just an old capacitor in the filter board)

 

[rotco]

Btw
I finally got the "special" ccapacitor for making myself an Audio Test Probe.
Maybe i can start with it and wait with the O-Scope.

Is there any thing i should be aware of while using it?
May i use it wherever i want?
Or maybe after the amp section while the signal is amplified, i need to prevent using it there? (Or even in the speakers terminals output)

What about the p.s?i can guess it's a circuit without a sound signal... Only electricity?
Ao i won't be able to find something there.. But..is it still safe to try there?

Sonce probably i wont know each point what is it exactly.. And might want to try "free" any point i see.

(Ofcourse i will track the route thru scheme, but in case i have a mistake)

Thanks

 

[mbz]

I use a software package that uses my PC soundcard, my cro's/tektronixs need a restore. The sound card needs to be
protected from excessive voltage otherwise it can be damaged. A series capacitor should be connected to block dc voltage, maybe 10nf or smalled?
A voltage divider should be considered if you are measuring large audio signal, ie, at the speaker posts. Typically a 1/10th divider is used, ie a 1 ohm
resistor in series with a 9 ohm resistor, measure voltages across the 1 ohm resistor. You only need the divider if you are measuring at the spkr posts.
The blocking cap is a must have.

 

[rotco]

Hi all
After a long time, i got back to this Akai AA-1030.
during all this time i learned a lot from you guys. thanks to you i acquired few tools and techniques of troubleshooting.

i will say that the "booming" noises i heared, appeared to be related to "too much" volume.
lately, i understood that the issue was that the audio signal came into the power amp board, but didn't actually amplified at the output of the board.
thus, while i try to raise the volume up, without the power amp actually raise the signal up, the volume knob was almost 80-90% but still the volume was low.

i started by validating all voltages at the p.s board outlets, and the power amp inlet voltages.
all appeared to be correctly. it was nice that in the service manual the desired voltages are marked in strategic points.
all the transistors legs in the power amp board measured correct. (8 for each channel - marked in yellow)

(i thought it's time to use the Audio probe i make in your recommend)
thus, i thought the next step is to track the audio signal from the AUX input, to the tone control, to the filter board, to the power amp board. it was present at all points.
also at the speakers terminals and the protection board inlet and outlet. (but not amplified, just normal noise).
thus i understood that the signal comes in to the power amp board, going out without actually amplified.

so next step was to track the signal from the first point in the power amp board.
after one-two moves inside, i find signal at one leg of electrolytic capacitor, but in it's other leg it wasn't present.

there are 7 electrolytic capacitors in the power amp board. i unsolder all of them. (3 for each channel, and big one in the center of the board marked in green)
i will order new ones and hope the issue will solved.

mistakenly, i desolder also other small capacitor, not electrolytic. im affraid that with the heat of the soldering iron i ruin it.
measured it with DMM, got 2uF.
i would like to replace it also if it already out.

how could i find replacement. i dont really know how to look for it. ( is it ceramic type? is it bi-polar? so while i solder it back, is it matter which leg goes to where?)
attached the photo, and the name of it from the s/m parts list.
VFM 82PF(K) 50WV.

Thanks all!

 

[blhagstrom]

I think that’s a ceramic capacitor.
It should be OK, just put it back. It doesn’t matter which way, they are not polar.

There is a thread about how to test transistors here. If you have a diode test setting on a meter, you can possibly figure out which transistor is bad.

 

[rotco]

I replaced all 7 electrolytic capacitors in power amp board.
Iasue remain the same.

Audio signal comes into the power amp board, and goes out of it in the same gain.

What can be tge issue?
Besides the two TO-3 output transistors, there is additional fove for each channel.

How can i track it? Where ia the issue?

I already checked the incomeing voltages to the board and they found correct.

Can i track it with Audio probe?
Is there any rule of thumb in here?
Like, whenever i pass thru electrolytic cap, the audio aignal should present at both legs in same level?
Whenever pass thru 3 pins of tranaistors.. Thru diode?

Thanks


Btw, i didnt change capacitors in the p.s board because i measured voltages at it's outputs, and they all seems correct according to the service manual.

 

[petehall347]

is this problem both channels or just one ?

 

[rotco]

is this problem both channels or just one ?

Both
Thats why it wierd that the issue related to the power amp.
But, if the signal comes to it.
Isnt it say that the issue is related to the power amp?
Sonce the sognal level goes out from the power amp on the same level ot comes into it.
Both channel speakers volume is low, although the volume knob goes up to 80%

 

[petehall347]

both channels says power supply .. unless previous history says otherwise .

 

[elnaldo]

Do you have a schematic? We must measure the signal and the voltages following the schematic, and the problem will show up. I suggest to stop replacing components without a reason, you can introduce more problems, and you will introduce more variables to the actual problem (if the problem persists, you'll start to doubt about the work you have done)

Do you have some pre-out - Main-in jumpers, to test each half of the amp separately?

Reading schematic at page 36 of the PDF downloaded from hifi engine, check you have the proper voltages (-39 and +39V) at the collectors of the output transistors. Also check the protection fuses F1 F2 on the Protection PC board, and check the speaker selector is clean and working. You can measure continuity WITH THE AMPLIFIER OFF AND UNPLUGGED, from the output transistors emitter to the speaker terminal at the back of the amp. It should be near 0.5 ohm with the speaker selected.

 

[rotco]

Unfurtunatley the receiver doesnt have preamp poweramp connctors.

Sure i have the schamatics.
And sure i didnt replace componnents by guess. I tracked the audio signal from the input to the output of the power amp board.
It goes out the same level it comes in.

Thats why i asked how can i track the signal "smarter" within the power amp.
I tried to move from the inlet step by step to the outlet, but i didnt know what to expect at each "jump".

I quite skipped the p.s capacitors replacement since i measure all the voltages at its output and they all found corrects according to the schematics.

 

[petehall347]

measure voltages at amp board

 

[sregor]

Check your grounds. Acts like ground not going t(or there is a bad trace) and causes no gain. With power unplugged, measure continuity to ground from different places on the board.

Edit: after looking at service manual - Check the amp board where C4, collector of TR3 and C10 Meet. That area should be grounded, and will give you no gain if not. (similar area for TR3b, C4b and C10b for other channel.

 

[rotco]

Further significant progress.

i found that the signal route is like that (of course):
1. Aux inputs
2. Tone control board
3. Filter board
4. Power amp board.

I did bypass on the filter board, and the issue solved. power amp acts correctly all good.
thus, the issue in the Filter board.
it split to half:
one segment related to Radio, with electrolytic caps and transistors... not my issue, at least for now.
one segment, simple circuit (ceramic capacitors and resistors). contains:
Low filter and High filter ON/OFF push switches.

the low filter works fine (make a change)
the high filter doesn't affect. cant hear any change. (its not bad contacts or cleaning, i already checked that) **im suspect that this is the root cause of the issue**

i see that while i insert 290mvac signal, it goes out after R3 resistor in about 6mvac. from after the resistor the signal continue to point #4 and from there to the power amp board. (also with Audio probe i loose almost all the signal after the R3 & R3b resistors)
there i loose all my signal.
is it normal to loose the signal so significant?! ( why anyway there is a resistor there from firstplace)
im so skeptical because i know that most of the time resistors doesn't goes bad.

is that makes any sense to feed the power amp with a signal magnitude of 6mvac? or 260mvac is more normal?

can you help?
thanks

note: the issue is the same both for L/R channel. i.e R3 & R3b acts the same.
in point 1&3 i feed in the signal of about 290mvac.
and it goes out in point 4&6 signal of about 6mvac.
i did it while both switches status are OFF (LIKE IN THE SCHEME)

 

[petehall347]

is the ground good at pin 5 ?

 

[rotco]

is the ground good at pin 5 ?

Yes
I measured there 0v

 

[petehall347]

both channels bad at that point ?

 

[petehall347]

i would check every resistor and capacitor around those switches and also make sure the switches are working correctly .

 

[rotco]

I never heard of bad resistors.
If it might be faulty, than it makes sense why the high filter doesn't affects.
The resistor already kills +90% of the signal prior to it.

Would you recomend testing R3 & R3b?
Yes, the signal almost dissapear after both resistors. (L/R channels i.e points 4 & 6)

 

[petehall347]

are high and low filter behaving the same way ?