nashou
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Post by nashou on May 2, 2019 18:47:36 GMT -5
Hi I have this nice shape QX-949A where it is in Protection. When I first got it to look over The relay would click after a long while and I was able to get a few DC measurements off the speaker Terminals but then its click out again going into protection. I have the Service manual and need some guidance , first in naming the channels. I measured the output voltages on the 3 output terminals of the power transistors and all but one measured in a similar voltage readings its the amp ,if looking from the front face, at the top right corner. the one in question measure over 39 volts at all pins IIRC as I did this latte last night.  The service manuals lines indicating the parts is faded and you can not make out what description goes to what part. So On that amp the readings across pins 1 and 2 was .5 volts way above the 20mV's it needs to be adjusted to. Adjusting VR3 got me to 240Mv's but it was jumping around as I tried sometimes hitting 3 volts dc. So something is amiss on that amp section possible. Where do I begin diagnosing this? I did a diode test of the output 's and all seem to measure ok , this was done in circuit for now. Removing them right now seems a task I'll wait for till they actually need to be removed. Athanasios |
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nashou
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Tech in Training.....
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Post by nashou on May 3, 2019 6:30:40 GMT -5
Doing some research is leading me to change out the 2SC1451 with newer ones as those are crap, and basically to change all transistors and some blue sanyo caps as well.
Will report back once i get the boards removed and put back in and tested.
Nashou
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Post by mastertech on May 3, 2019 11:05:55 GMT -5
My first suggestion would of been to test all the rail voltages. But since you have already disassembled some I guess you will have to see what comes later.
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nashou
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Post by nashou on May 3, 2019 14:19:51 GMT -5
My first suggestion would of been to test all the rail voltages. But since you have already disassembled some I guess you will have to see what comes later. No I haven't disassembled it yet. I was planing on measuring the voltages on Page 98 of the service manual. Nashou |
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nashou
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Tech in Training.....
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Post by nashou on May 3, 2019 15:59:23 GMT -5
Here is what the Voltages on that amp board should be. Hopefully I can get around to it this weekend.  |
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Post by mastertech on May 3, 2019 22:02:28 GMT -5
Make sure you also test the output line of each amp for 0v.
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nashou
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Post by nashou on May 4, 2019 18:54:26 GMT -5
Make sure you also test the output line of each amp for 0v. Ok all voltages tested ok except pin 4 (bottom Left in pic) on the left side board in pic I think this is Chanel one ( Left front channel? ) . Should be 0 is +13.4 VDC .  Athanasios |
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Post by mastertech on May 5, 2019 13:03:34 GMT -5
Is that suppose to be an audio output line? It would help if I knew just what line that was and maybe even which amp that is.
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nashou
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Tech in Training.....
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Post by nashou on May 5, 2019 14:15:51 GMT -5
Is that suppose to be an audio output line? It would help if I knew just what line that was and maybe even which amp that is. Yeah I know, I'm having a hard time figuring out which amp it is as well. I think that board is for Channel one and 4 Left front and left back I think. here is the pin out drawing. Looks like 4 goes to 16? on the protection circuit board.   |
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Post by mastertech on May 5, 2019 16:49:02 GMT -5
Are the pin numbers marked on the board? How do you know that is pin 4 and not 23?
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nashou
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Post by nashou on May 5, 2019 18:20:02 GMT -5
Are the pin numbers marked on the board? How do you know that is pin 4 and not 23? Yes they are marked  |
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nashou
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Post by nashou on May 5, 2019 18:35:34 GMT -5
It looks like on each board ( two of them) 4 and 5 and also 22 and 23 are tied together respectively . Where 4and 23 on the Channel 1 and 4 board( lets call it board A) go to the protection board whilst 5 and 23 go to the speaker relay I assume.
On Board lets call it B channel 2 and 3 , 5 and 23 go to protection board and 4 and 22 go to relay.
So the protection board is detecting the 13.xx volts on pin 4 sending it to pin 16 on the protection board therefore tripping the relay.
Am I correct?
Nashou
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Post by mastertech on May 5, 2019 19:33:14 GMT -5
Ok, I think I got it. I have marked your image. I believe you meant pin 4 is as marked and in has 13.4v on it. If correct then remove the wire from pin 10 as marked and see if you still have the 13.4v on pin 4.  |
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nashou
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Post by nashou on May 5, 2019 20:03:40 GMT -5
Ok, I think I got it. I have marked your image. I believe you meant pin 4 is as marked and in has 13.4v on it. If correct then remove the wire from pin 10 as marked and see if you still have the 13.4v on pin 4. Ok I see where your going and I was also thinking it was the control board . I don't like unwinding wire wrapped connections So I measured that pin and the other pins 17, on that board and 10 and 17 on the "B" board all the other pins measured in the mV's whilst the pin you asked me to measure came in at - 5-6 VDC. I could remove it if you insist , I was hoping I could get in there with a solder Iron and remove the pin but its tight. I read that on that board there are many light blue sanyo lytics that short . and they need to be replaced . Tired right now So If i need to still remove that pin I'll do it tomorrow after work . And not looking forward to getting at the control board lol. Any thing else? |
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Post by mastertech on May 5, 2019 20:15:45 GMT -5
So I measured that pin and the other pins 17, on that board and 10 and 17 on the "B" board all the other pins measured in the mV's whilst the pin you asked me to measure came in at - 5-6 VDC. Can you clarify this sentence. I am not getting a clear picture. |
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