issue with AKAI AA-1030 Receiver

[petehall347]

ah .. R4 and R4b are grounded at one end ... high filter shorts these out ..

 

[petehall347]

try a signal to R3 try both . both ends

 

[rotco]

are high and low filter behaving the same way ?

i already says that low filter does affect while pushing switch in/out
but high filter doesn't.

try a signal to R3 try both . both ends

i already says message #54 before:

"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)"

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

 

[petehall347]

so i understand more ..what happens if signal is injected at pins 4 and 5 ?

 

[rotco]

so i understand more ..what happens if signal is injected at pins 4 and 5 ?

i really getting hard to understand you properly.
my english is basic.

number 5 is grounding point.
what do you mean to inject signal to 4 and 5 points?

i says that in points 4&6 the signal almost dissapear, but before resistors R3 and R3b the signal is healthy.
i.e R3 and R3b is almost killing my signal.
is it should be like that?

 

[petehall347]

trying to see if it is after r3 that is the problem
sorry yes 4 and 6 .. my eyes are not so good ..

 

[petehall347]

how did you bypass filter board ?

 

[rotco]

how did you bypass filter board ?

Used aligator clips both sided. From points 1& 3 of filter board. To two points on the inlets of power amp board.

 

[sregor]

Look at muting circuit. You can bypass muting by disconnecting wires between 4and 13 and between 6 and 15. The muting circuit uses TR3 and TR4 on the filter board to mute signal on turn on. IS not part of FM muting which is also on the filter board. If you disconnect muting, you may get more noise on turn on.

 

[rotco]

Look at muting circuit. You can bypass muting by disconnecting wires between 4and 13 and between 6 and 15. The muting circuit uses TR3 and TR4 on the filter board to mute signal on turn on. IS not part of FM muting which is also on the/ filter board. If you disconnect muting, you may get more noise on turn on.

Thanks a lot!
I will try!
Altough actually on board i dont have this "jumper wires shortcuts"
Like everytime...the scheme is different then reality!

Also, i found missmatch voltages value that comeing from p.s board to filter board.
Mayve thats the reason TR3 & TR4 doesnt make rheir job.

On filter board pin #11 is at 30v instead of 50.2v.
This pin fed by pin #14 on p.s board. Which there i measure also thr 30v.

 

[rotco]

Look at muting circuit. You can bypass muting by disconnecting wires between 4and 13 and between 6 and 15. The muting circuit uses TR3 and TR4 on the filter board to mute signal on turn on. IS not part of FM muting which is also on the filter board. If you disconnect muting, you may get more noise on turn on.

But
Before i dive deep into the boards and start replacong componnents.

Did you see that i found that most of the signal disaapear after resistors R3 & R3b?
Bith with DMM and Audio probe.
I found that before the resistors the voltages are about 300mvac, and after about 5mvac.
Alao the sound almost dissapear after the resistors.

From there ot goes directly to 4&6 pins and from there to the inputs of the power amp board.

The 13 & 15 pins of folter board might be in short woth points #4&6.
But, if the signal doesn't present there. Is it affect at all?

Thanks

 

[sregor]

Muting transistors should have -1.2 (not exact) and should be non conductive - when they conduct, they pull the output on pins 4 and 6 to ground, which sounds like your problem. The turn on process puts a positive voltage on the basis, but the -39 from pin 12 pulls it negative. So check 12 for -39 on filter board too.

 

[rotco]

Muting transistors should have -1.2 (not exact) and should be non conductive - when they conduct, they pull the output on pins 4 and 6 to ground, which sounds like your problem. The turn on process puts a positive voltage on the basis, but the -39 from pin 12 pulls it negative. So check 12 for -39 on filter board too.

pin #12 does have -39v.

so, is that means that the issue is within TR3 & TR4 themself?
how can i check that?
by validating 1.2v on the base, and 0v on both collector and emitter?

 

[petehall347]

On filter board pin #11 is at 30v instead of 50.2v.
This pin fed by pin #14 on p.s board. Which there i measure also thr 30v.

check all the other power supply voltages .

 

[sregor]

Looking at schematic - 50.2 volts is probably a misprint.
The voltage should be negative on bases - the transistor should not be conducting. (circuit makes it conduct to mute signal on turnon)
Did you figure out how to isolate 13 and 15 from 4 and 6 - not clear how they are actually connected.

 

[rotco]

Did you figure out how to isolate 13 and 15 from 4 and 6 - not clear how they are actually connected

Its printed on PCB.
So i guess the only way to isolate is by disconnect the transistors.
I rather solve the issue than isolate the problem.. (Of course just for troubleshooting)
Unfurtunatley i go aboroad for two weeks so i will bring back an update after my return.
I will take a photo of the actually board, which is slightly different then the scheme.

Looking at schematic - 50.2 volts is probably a misprint

Can you tell what suppose be the desired voltage on pin #11 at filtrr board if 50.2v is a misprint?
I attached the power supply scheme, pin #14 is supplying the voltage to it.
I marked on screenshot, the voltage should be lower then 49.3v since it after a resistor.
On the other route.. It connected to capacitor c13 10uf, 50v to grounding.. (37.8v is a misprint)

Thanks!

 

[rotco]

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.

DMM beeps for continuity. 0.8ohm for the all 4 emitters.

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

I tested. They all grounded.

 

[rotco]

not clear how they are actually connected.

Yes
Its quite hard to understand since the scheme doesn't fits the actual board.
I tried to take some photos, and marked what i could identify.
More points can be identify if i track for continuity with DMM.
Thats what i have until now, hope that it will help.
Note that in scheme there are 4 transistors. On board actually there are 5.
Also, it can bee seen that the printed conductive from points 4 & 6 doesnt go to the corner of the board as describe in scheme.
I said, its quite different.

 

[rotco]

Hiiii
I found another AK thread of issue exactly like mine!
The guy there also found that its related to the filter board.
But he didnt poat the final resaults what was bad.
It's from the beggining of 2018, and you guys also tried to help him.
@elnaldo @petehall347

Ive asked him there to share it's final findings.
Hope he will see it and still visiting AK.

I found his thread while google the version of that filter board i have which different from the one in the s/m.

Here is the thread:
http://audiokarma.org/forums/index.php?threads/akai-aa-1030-very-low-volume.807492/

 

[sregor]

Pin 12 calculates to be around +42 V.
Unsoldering collectors of muting transistors should allow full output if this is where the problem is.
Checking base voltages should tell something
No idea what other transistor is doing. Good Luck