Re: Aiwa BX-770 pre-amp outputs only ~120hz HUM
ITS ALIVE!!
At last I was probing with my headphones on IC5 the (double?) op-amp I noticed the sound wasn't solid on pin 2 ( the output) but figured since i was just standing over it with wires it was fine. moved onto the connector right next to it that runs the sound to the front board with the GEQ and there was no output there but then thought maybe im on the wrong pins. i also noticed some static poking around when i touched it.
Fast forward to just now I got back at...
waspie
Member
Last Activity: 12-30-2022, 09:53 PM
Joined: 11-29-2022
Location: munroe falls
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Re: Aiwa BX-770 pre-amp outputs only ~120hz HUM
This will kind of be my notepad so if it gets annoying just don't pay any attention. I don't have a scope so I'll just try and trace the audio as far as I can go. So far ic4 seems fine as does ic5 the next in line. I can't seem to pick it up at the GEQ IC. It's either lost at the connector to the front board or?? I need more time to double check I'm probing the right spots ( ic2 19 ground 15 signal). 3 small kids and a wife makes this a difficult process!Leave a comment:
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Re: Aiwa BX-770 pre-amp outputs only ~120hz HUM
They don't seem to be for the few minutes I have it on but evidence on the board would say they run hot. +12 rail measures at ~12.67v
They must have been. I've ordered some replacements but in the meantime I paralleled 2 220uf caps for each one and the hum seems to be gone. Also replaced the 8.2k resistor that was blown apart.
I don't know anyone with a scope and don't have much intention on buying one at the moment.
So, I replaced...Last edited by waspie; 12-26-2022, 10:02 AM.Leave a comment:
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Re: Aiwa BX-770 pre-amp outputs only ~120hz HUM
Q21 is showing a touch over 12v. I'll check their temps later - probably tomorrow....Leave a comment:
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Re: Aiwa BX-770 pre-amp outputs only ~120hz HUM
Q23 is supposed to have -19.2 and -14.4 and -13.3. The 14.4 is showing -9.3
the -13.3 is -10.7
Would those voltages indicate a problem with Q23 or something else dragging it down (up?)?
Those caps right next to it look like they've lived a hard life. I figure I'll replace those. Also the resistor just to the side of Q21 looks partially blown apart. Surprisingly it ohms out at 5.7k but that doesn't seem to match up with its bands, not that I can tell what they're supposed...Leave a comment:
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Re: Aiwa BX-770 pre-amp outputs only ~120hz HUM
potential silly question... can i test if they're shorted while in place or do they need removed?...Leave a comment:
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Aiwa BX-770 pre-amp outputs only ~120hz HUM
I had another thread for the amplifier component of a mini system that had some issues. those are resolved via replacement of the 4 power supply filter caps.
The pre-amplifier of this system also has a problem. It outputs a powerful ~120hz hum. The amplifier has a spectrum analyzer with a 125 hz position and that's where it lights up. On the pre-amp is an equalizer. If I move that slider or one on either side up the spectrum analuzer at 125hz will just about peg at the top and this is audible through the speakers.
This system uses a proprietary interconnect cable.... -
Re: Aiwa GX-770 Amplifier Protection Circuit
Success! the amplifier works! The original STKs seem fine (as shown in the pictures).
The pre-amp however does not. I'll start a new thread for that
I put it all together and am getting an intense hum around what I'm assuming as 120hz (the spectrum analyzer has 125 listed out).
If I unplug the pre-amp input to the amp the amp falls silent. Using the headphone output of a portable audio device and some test leads I input sound into the amplifier et voila! it works, both channels.
If...Leave a comment:
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Re: Aiwa GX-770 Amplifier Protection Circuit
Don't answer that last one, i didn't have the patience.
With 4 new caps in i powered it up and all the relays came on as i expected
Soldered the original STKs in, powered it up again and all the relays clicked.
I'll be putting it back together now but cannot test further until i have fuses again since i blew all of them from the bad caps.Leave a comment:
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Re: Aiwa GX-770 Amplifier Protection Circuit
Hey folks, caps finally came in.
To recap, at least 1 cap in both sets of the big caps were bad. one was completely shorted and the other couldn't hold voltage for any reasonable length of time.
The caps are soldered in. The STKs are currently removed.
Is it OK to put power to it with the STKs removed?Leave a comment:
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Re: Aiwa GX-770 Amplifier Protection Circuit
Great info, thanks fellas.
I did check the headphone jack previously and it looked good. After desoldering the STKs yesterday I briefly powered it and it was blowing the main fuse pretty quick.
I found one of the smaller of the two large sets of filter caps completely shorted. For the time being I'll be waiting on the new caps to come in.
I'll be checking those pots, thanks.Leave a comment:
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Re: Aiwa GX-770 Amplifier Protection Circuit
took the covers off
*edit*
Looking at these with the caps off I don't see anything blown/burnt. All the wires are intact and all the components *look* fine....Last edited by waspie; 12-05-2022, 07:57 AM.Leave a comment:
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Re: Aiwa GX-770 Amplifier Protection Circuit
definitely!
STKs should be here today and I'll have time to solder them in tomorrow.
I'll probably still be waiting as one of the larger of the two filter caps has a bulging top and replacements are on a slow boat.
I'm assuming powering it up with a bad cap is a bad idea.
As for the solder, it all looks pretty good. I haven't gone over it with a fine tooth comb or anything but its all nice and soft solder and there's no obvious cracks anywhere. The only 2 things remarkable...Last edited by waspie; 12-05-2022, 06:14 AM.Leave a comment:
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Re: Aiwa GX-770 Amplifier Protection Circuit
If it's worth anything, the relay was never engaging even from start. Not sure that that actually changes anything
Thanks guys, I'll put the caps back on and test....Leave a comment:
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Re: Aiwa GX-770 Amplifier Protection Circuit
no need to be rude, i didn't know.
Measuring resistance between 2 and 3 / 8 and 9 on both ICs shows near infinite.
I guess I was expecting the typical burnt component smell if these were bad and it's not there...Last edited by waspie; 11-30-2022, 08:26 PM.Leave a comment:
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Re: Aiwa GX-770 Amplifier Protection Circuit
Jumpering the relay with no source connected still produced a significant hum = bad caps, right?
Pulled the 2x 56v 5600uf and 2x 56v 6800uf caps and put it back together as little as I could. powered up and the protection relay is closing now.
3 of the 4 caps I can set upside down and they sit flat but 1 of them definitely has a slightly pushed up top. I guess i'll try replacing these 4 caps firstLeave a comment:
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Re: Aiwa GX-770 Amplifier Protection Circuit
Some snips from the manual to highlight what i'm referring to
Attached...Leave a comment:
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Aiwa GX-770 Amplifier Protection Circuit
I am by no means an expert on this type of troubleshooting but I can follow direction real well.
I'm no stranger to using a meter and soldering iron so I'm looking for some help in fixing an old amplifier/system I got. This is part of a system "V-1200" by Aiwa where there are several components. My first problem seems to be the amplifier.
It seems to be in protection. When first turned on I hear the inital relay coming on but never the second relay which is connected to the protection IC. I don't see any obvious bad components on the board. If I ground the... -
Re: New Members - please post your introductions here
New guy here, hoping to find some help on an old Aiwa system i've just received.Leave a comment:
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