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Old 06-11-2018, 01:17 AM   #1
perette
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Default Aiwa CA-P50, low power output

hello

I've got an old Aiwa CA-P50 power amplifier with its preamp.
when connected to HP, the sound power is very low and full of distortion. Both channels are in the same state

I've tested with another preamp (and vice-versa) that the problem is in the amplifier.

what I've done so far

- checked all ref voltages. OK
- changed all electrolytic caps
- not changed 4 electrolytic bipolar ones.
- not touched the zero power and any other adjustment
- checked and/or resolder questionnable ones.

when I use a headphone, the sound quality is better, but the power is very low.

and now I'm lost

here are some pict of the beast.
I'll post also drawings and info on the amp later today

Help is welcome.

best regards

JM
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Old 06-11-2018, 01:30 AM   #2
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Default Re: Aiwa CA-P50, low power output

Hi everybody

tech info.

JM
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File Type: pdf hfe_aiwa_st-r50_sa-c50_sa-p50_h_u_service_en[1].pdf (18.60 MB, 15 views)
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Old 06-11-2018, 07:00 AM   #3
Andrew F. Ali
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Default Re: Aiwa CA-P50, low power output

Did you test the Output ICs?
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Old 06-11-2018, 07:15 AM   #4
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Default Re: Aiwa CA-P50, low power output

If all fusible resistors have been checked?
Thermal fuses CB1,CB2 + relay S4 are OK?
What value is the idling current and voltage on the R51(resistor on the bases of the output transistors) and next resistor on the R-chann ?
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Old 06-11-2018, 07:21 AM   #5
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Default Re: Aiwa CA-P50, low power output

Quote:
Originally Posted by Andrew F. Ali View Post
Did you test the Output ICs?
What the Output ICs you mean?
This amp does not have any output ICs in the signal path between IN-OUT.
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Old 06-11-2018, 07:23 AM   #6
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Default Re: Aiwa CA-P50, low power output

Output transistors are what I meant. Not ICs.
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Old 06-11-2018, 07:28 AM   #7
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Default Re: Aiwa CA-P50, low power output

Hello.

@andrew. I'm a newbie on this exercise. How to test them?

@piotr.
I will check them specifically this evening

Thanks for your input and advices.

I keep you informed of the outcome.

Best regards from France

Jm
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Old 06-11-2018, 07:52 AM   #8
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Default Re: Aiwa CA-P50, low power output

The Output Transistors are the big ones on the metal heatsink. Two on the left and two on the right.
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Old 06-11-2018, 08:03 AM   #9
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Default Re: Aiwa CA-P50, low power output

Hi andrew.

I'll check them this evening.

I was just balancing between testing on the unit, active way and as a stand alone transistor.

Best regards

JM
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Old 06-11-2018, 09:46 AM   #10
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Default Re: Aiwa CA-P50, low power output

So what Voltage testing have you done so far?
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Old 06-11-2018, 10:26 AM   #11
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Default Re: Aiwa CA-P50, low power output

Hi Budm

Tested all test points as described in the service manual except the zero and idle values.

All values seems to be ok (or in the range).

Best

JM
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Old 06-12-2018, 04:02 PM   #12
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Default Re: Aiwa CA-P50, low power output

Since the output seems to be distorted (but is otherwise okay at lower power or on headphones - i.e. no blown fuses or shorted power rails), I suggest looking into the pre-amp / driver section of the amp, particularly if the op-amp IC (if any) are getting proper power. I'll have a look into the SM later tonight on my desktop and see if I can point you to check something (this laptop I'm on now is on a slow connection and also not great for viewing big service manuals).

P.S. If I forget to reply, just bump this thread.
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Old 06-13-2018, 12:10 AM   #13
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Default Re: Aiwa CA-P50, low power output

Hello everybody

sorry for my silence, i was travelling for buisness.

thanks for all your input.
i'll check power transistors today.

@momaka. just to avoid any "wrong path", sound on speaker is low and always distorded as long as I can hear something at less than 1/4 of the volume pot.
on headset, yes sound is correct, but you must turn the volume at more than half of the max to hear at normal volume in the headset.

thanks again. i post you the outcome of power transistor testing.


JM
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Old 06-13-2018, 03:15 PM   #14
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Default Re: Aiwa CA-P50, low power output

Hello everybody

Tested power transistors and resistor around. All seems to be OK. None open.

I've also had a look on fuse resistors on each channel board. R47 R47, R49 and R50 who are supposed to be 200 ohms. It looks like they are all opened.
Tested Q11 to Q14 and they are looking OK.

From there, where is the next step?

Best regards

JM
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Old 06-13-2018, 03:16 PM   #15
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Default Re: Aiwa CA-P50, low power output

Sorry R47 to R50 are 100 ohm on my model. But whatever scale I use they are open.

JM
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Old 06-13-2018, 05:35 PM   #16
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Default Re: Aiwa CA-P50, low power output

Since BOTH channels have the same symptom then it must be failure in section that is common to both channel.
Can I see the pictures of the front and rear panel?
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Old 06-13-2018, 08:19 PM   #17
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Default Re: Aiwa CA-P50, low power output

If R47 and R49 are open, check Q7, Q9, Q11 & Q13, if they are ok you might get lucky by just replacing the resistors. Try replacing them on that channel and see if you get audio on that side. If it works replace them on the other channel.
Since they are a fuseable, they may have just opened.
To get any audio with those resistors open would likely be through D33 & D35. The relay would also need to be closed for any audio to get to the headphones so dc offset is also likely close to zero

Last edited by R_J; 06-13-2018 at 08:26 PM..
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Old 06-14-2018, 12:23 AM   #18
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Default Re: Aiwa CA-P50, low power output

Hello everybody

Will do it.
- pictures of the front panel, there is no back panel (just connectors)
you have the main board (where the big power source is located ), two side panels for each channel and one front that hold display leds.
- test on Q7, 9, 11 and 13.
this evening. Now its time for business.

many thanks for your help.

JM
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Old 06-14-2018, 12:56 AM   #19
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Default Re: Aiwa CA-P50, low power output

"- pictures of the front panel, there is no back panel (just connectors)" I want to see what they have on the front and on the back, it does not matter if they are just connectors or not, I just want to see what we are dealing with.
BTW, what is the history of this unit? Did both channels just went bad at the same time? I can see one channel may have failed, but both with the exact same symptom must be really bad luck.

Last edited by budm; 06-14-2018 at 12:59 AM..
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Old 06-14-2018, 01:13 AM   #20
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Default Re: Aiwa CA-P50, low power output

Hi budm

Here are pictures.

Unfortunately, no real story available.
This unit was dropped to waste by one of my neighbors.
Whenever there is a single pop when turning the volume pot, they put the all stuff to waste without further questions.
Hi have saved many tv and audio units over passed years.
But I never faced this type of problem and I can't decide to put to waste something that can be saved.

Jm
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File Type: jpg IMG_20180614_090342.jpg (398.3 KB, 7 views)
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