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-   -   Help with Power Acoustik PA-300 (http://www.diyaudio.com/forums/car-audio/177042-help-power-acoustik-pa-300-a.html)

Mote 10th November 2010 10:40 PM

Help with Power Acoustik PA-300
 
3 Attachment(s)
It is a 4 channel amp based on 2 IC-s, TDA8563Q.
I get no audio from 1st, 3rd, 4th channel. Audio is only in 2nd channel but it seems to be not amplified and sounds like its coming from a broken tweeter. I dont have an oscilloscope, cant analyze the sound. On 3rd channel I have dc voltage on 1 and 2 - nothing.

Found datasheet for TDA8563Q, legs 3 and 10 are supply and 5 is ground, between 3 and 5, 10 and 5 i have 11 volts on both ICs.
Legs 1 and 13 are inputs, 2 is signal ground, between 1 and 2, 13 and 2 i get 0.09 volts on both ICs when audio is fed to input.

There are some dual op amps on the board as well. 455800 JRC 7021B?, supply and ground are legs 4 and 8? I got 8.8 volts between 4 and 8 on both of these. Legs 1 and 7 are outputs. If I want to measure the output voltage then I measure voltage between leg 1/7 and ground? 2 and 3, 5 and 6 are inputs. Between 2 and 3, 5 and 6 i get voltage 0.09.

Is there a simple way to test opamps and ICs whether they are OK or not?
Right now i would just change ICs and see what happens, one of them is clearly blown if dc voltage is on output?

DC voltage on output is between blue and green wire, marked C on board (left side IC). Noisy low volume sound is coming from 2nd channel (right side IC)

Perry Babin 11th November 2010 05:54 AM

The op-amps are likely NJM4558s.

If the op-amps have supply voltage (~10v on pin 8 and 0v on pin 4), the two inputs for each op-amp should be very close to the same voltage (within 0.010v) and should probably be at 1/2 of the supply voltage.

When the output ICs are working properly, you should see 1/2 of the battery voltage on the speaker output terminals.

Mote 11th November 2010 10:21 AM

Opamps:
Did I understood correctly that between leg 8 (V+) and ground I should get supply voltage, I measure 8,5 volts. Between leg 2 (- input) and ground there should be half of the supply voltage? I measured 4,42 V, between leg 3 (+ input) and ground I measure 4,37 V. I get similar results from all the 4 inputs on both opamps. Between output and ground there is also the same voltage.

ICs:
I got a bit confused again and dont know if I understood correctly. I need to measure each speaker output to ground? (Sorry, im a noob :( )
If so then results are these:
1: 0,02
2: 0,03

3:0,00
4:0,00

5:2,03
6:2,84

7:0,00
8:0,21

Perry Babin 11th November 2010 11:56 AM

The op-amps seem OK. If the ICs have supply voltage on their power supply pins, They appear to be defective. Generally, this type of IC will crack open on its face when it fails. Are yours cracked?

ppia600 12th November 2010 03:50 AM

I would suspect the IC's first, otherwise maybe the solder joints where the rca jacks meet the pc board.

Mote 12th November 2010 06:41 PM

RCA jacks and solder joints are OK. ICs have no cracks at all but there are no other components which could have failed? Board is looking good, joints and traces also...

I get this noisy low volume audio on channels 1 and 2 now, 3 and 4 are quiet and IC responsible for making channels 3 and 4 work gets much hotter than the other.
I use a 500W PC power supply to test the amp, the moment I switch it off - volume of the audio increases for a second before amp switches off. Unsoldered the supply legs of the hot IC and tried then but that improved nothing.

I can order through local electronics shop TDA8560Q chips I suppose that it is OK to use them because I did not find any differences in datasheets of TDA8560Q and TDA8563Q, besides the title.

Perry Babin 12th November 2010 07:40 PM

The gain of the two ICs is significantly different. For a fixed signal level, one would be producing less than 1 watt while the other would be driven to clipping. This may not be a problem but you should be aware of the difference.

Mote 12th November 2010 07:50 PM

You are referring to Gv - closed loop voltage gain?
tda8563Q - 26 dB
tda8560Q - 40 dB

Do you agree that ICs need to be replaced and that should make the problem go away?

Perry Babin 12th November 2010 07:55 PM

Yes.

From the information you've provided, the ICs appear to be defective but I can't guarantee that it will solve your problem.

I don't know what replacement parts or amps cost where you live but here, it would be less expensive to buy a comparable amp as a replacement.

Mote 12th November 2010 08:09 PM

You are about right, I bought this one for 100 kroons and replacement ICs will be 120 kroons. But I am interested in electronics and I think that while I am trying to repair a amp I will also learn something new.


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