AKAI AM-U55 gibt keinen Ton von sich

Ich sehe, daß das ein Verstärker mit einem Endstufenhybriden (STK2155) ist. Halt, da ist noch einer, STK3082, der macht wohl den Treiber. Einer von beiden wird wohl hopsgegangen sein (im Zweifelsfall würde ich sagen der 3082, aber das ist jetzt Bauchgefühl).

Als erstes die symmetrischen Betriebsspannungen nachmessen (z.B. an den dicken Siebelkos), und dann kannst du dir die Datenblätter zu den STKs besorgen und dort fleißig Spannungen messen.

Wenn du schon mal am Reparieren bist, tausche am besten alle kleinen Elkos in der Nähe der STKs gleich mit.

Hi,

im Zweifelsfall würde ich sagen der 3082, aber das ist jetzt Bauchgefühl

...and a very good one. I have replaced several of these chips in Akai amplifiers of this series.
There is a new and better version STK3082-III available at a reasonable price from ASWO, Germany, partno.:989620

Remember, ASWO is a whole-dealer. You need to ask a shop that deals with them to order it.
Don't forget to:

tausche am besten alle kleinen Elkos in der Nähe der STKs

and re-solder the STK2155 just in case.

mfg,

/tri-comp

Vielen Dank Leute! Dann werd ich mal meine Werkzeugkiste rausramen...

Hmm, habe soeben die Spannungen am stk 3042 nachgemessen mit folgendem Ergebniss:

Für den linken Kanal stimmen sie mit dem Sollwert ziemlich überein, am rechten Kanal allerdings liegt an 2 Pins 45 V anstatt 1,2 /-1,2 V an. In Folge davon liegen auf der rechten Seite des stk 2155 ebenfalls zu hohe Spannungen an.

Lohnt es sich bei diesem Wissenstands einen neuen stk 3042(3082) zu kaufen?

lg

Oops....
Checked the service-manual and there IS a STK3042 in this amplifier, NOT STK3082.
It really doesn't make much of a difference as they are the same chips just the 3082-version will run on higher supply voltage.
If you prefer to use the original chip it is also available from ASWO (in the upgraded STK3042-III version), partno.: 963400. It is about 1 Euro cheaper than 3082-III.
Of course the chip is defective when you have +45V on Pin-2 but I suspect that you are NOT talking about Pin-2 but instead about Pin-6, the positive drive output-pin or Pin-5, the negative drive output-pin. In any case the chip is dead.

mfg,

/tri-comp

Hmm, habe jetzt den stk 3042 ersetzt, allerdings tritt noch immer das selbe Problem auf. Bin grade ziemlich sauer über die unnötige Investition und denke, dass der Fehler wohl früher in der Spannungsversorgung liegen muss. Nur wo?

jnrs90 schrieb:

Für den linken Kanal stimmen sie mit dem Sollwert ziemlich überein, am rechten Kanal allerdings liegt an 2 Pins 45 V anstatt 1,2 /-1,2 V an. In Folge davon liegen auf der rechten Seite des stk 2155 ebenfalls zu hohe Spannungen an.

Es könnte natürlich auch sein, daß es umgekehrt ist. Hast du schon mal den STK2155 im stromlosen Zustand auf Kurzschlüsse geprüft?

Bin grade ziemlich sauer über die unnötige Investition

What do you expect from people here?
YOU and YOU alone is responsible for what ever decisions you make. We try to relay our experience, free of charge, but we can't always be right. It would take a professional tech about 2 min's to find out exactly WHAT is wrong with this AKAI. Of course he should have it in front of him along with a volt/ohm-meter.
As I wrote, I have repalced several of the STK3042/3082 chips and NEVER the output chip itself. That doesn't mean it can't be defective; it can easily. To check if it is shorted is simple as audiophilanthrop suggests, but you should still know your way around a schematic diagram and the volt/ohm-meter.
Now, I would like to know of what IC/PIN-2 you have the +45V? The STK3042 or the STK2155?

mfg,

/tri-comp

tri-comp schrieb:

.....

Im sorry, I think you misunderstud me. I'm very happy you guys here are helping me! I really didn't want to blame any of you. I was just angry that I bought that new STK without doing more research.

Again, thank you very much fo your help!

tri-comp schrieb:

Now, I would like to know of what IC/PIN-2 you have the +45V? The STK3042 or the STK2155?

Problem is, there still are 45Volts on pin-2 of the stk3042 and stk2155.

lg

OK, no problem.

On PIN2 of the STK2155 is the supply-voltage directly from the power-supply so you should have around +45V here. The actual value is not critical. +/-3V is OK.

Here is the list of expected voltages on both IC's:

STK3042:
Pin1 = 0V (Left-Input)
Pin2 = 0V
Pin3 = 40.5V
Pin4 = 40.1V
Pin5 = -1.3V (Left-Output)
Pin6 = 1.2V (Left-Output)
Pin7 = -41.7V (-Supply)
Pin8 = 0V (Ground)
Pin9 = 41.2V (+Supply)
Pin10= 1.2V (Right-Output)
Pin11= -1.2V (Right-Output)
Pin12= 40.5V
Pin13= 40.1V
Pin14= 0V
Pin15= 0V (Right-Input)

STK2155:
Pin1 = 1.2V (Input-Right)
Pin2 = 43.3V (+Supply)
Pin3 = 0V
Pin4 = 0V (Output-Right)
Pin5 = 0V
Pin6 = -43.3V (-Supply)
Pin7 = -1.2V (Input-Right)
Pin8 = No Connection
Pin9 = No Connection
Pin10= -1.3V (Input-Left)
Pin11= -43.3V (-Supply)
Pin12= 0V
Pin13= 0V (Output-Left)
Pin14= 0V
Pin15= 43.3V (+Supply)
Pin16= 1.2V (Input-Left)

On the STK2155 there MUST be shorts between Pins 3,4,5 and between Pins 12,13,14 but NOT from Pins 11,15 to Pins 12,13,14 and NOT from Pins 2,6 to Pins 3,4,5

If you haven't got the schematic diagram I can help.

mfg,

/tri-comp

tri-comp schrieb:

STK3042: Pin1 = 0V (Left-Input) |0 Pin2 = 0V |0V Pin3 = 40.5V |27V Pin4 = 40.1V |27V Pin5 = -1.3V (Left-Output) |-1,5V Pin6 = 1.2V (Left-Output) |1V Pin7 = -41.7V (-Supply) |-46V Pin8 = 0V (Ground) |0V Pin9 = 41.2V (+Supply) |+28V Pin10= 1.2V (Right-Output) |+45V Pin11= -1.2V (Right-Output) |-45V Pin12= 40.5V |40V Pin13= 40.1V |40V Pin14= 0V |0V Pin15= 0V (Right-Input) |0V STK2155: Pin1 = 1.2V (Input-Right) |1,1V Pin2 = 43.3V (+Supply) |+47V Pin3 = 0V |0V Pin4 = 0V (Output-Right) |0V Pin5 = 0V |-47V Pin6 = -43.3V (-Supply) |-47 Pin7 = -1.2V (Input-Right) |-1,4V Pin8 = No Connection |0V Pin9 = No Connection |0V Pin10= -1.3V (Input-Left) |-47V Pin11= -43.3V (-Supply) |-47V Pin12= 0V |-47V Pin13= 0V (Output-Left) |0V Pin14= 0V |47V Pin15= 43.3V (+Supply) |47V Pin16= 1.2V (Input-Left) |45V

Hi,

+28V at STK3042 Pin-9 is NOT possible unless FR3 is defective or really, really warm. It must be dissipating around 3.5Watt and that's a lot!
Check if it's 100 Ohm or not and of course if it's WARM.

mfg,

/tri-comp

Which ressistance do you mean by fr3?
The marked ones?
http://img217.imageshack.us/img217/8199/widerstandd.png
I checked them, both have about 1k Ohm.

lg

No, not R3 but FR3.

Follow the PCB-wire from Pin-9 of STK3042 to the right and up on your picture. (Actually you just cut-off the interesting part to the right)
At the edge at the PCB, just under where it says 'AMUZ-401' you will find FR3. It is 100 Ohm and VERY HOT if it is still 100 OHM. Of course I hope it is defective and has a bigger resistance-value now.

/tri-comp