CS 800 Had Fading Channel B but Now has no power

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7rrivera7
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CS 800 Had Fading Channel B but Now has no power

Post by 7rrivera7 » Sun Jan 02, 2022 1:53 pm

Model: CS 800X
Serial: 09593008
MFG LOC-10 00319510/JHI30

Yesterday I powered up my CS 800 after being in storage for 10 years. I connected my JBLs using 1/4" phono plug output jacks and a tablet with a 3.5mm headphone jack to dual RCA's and converted to 2 phono plugs - one into each channel's high Z inputs. Everything looked and sounded fine and I had music on both channels.

After about 10 mins, the volume on channel B went low. I tried adjusting the gain but it was not outputting like channel A. I turned the amp off and on and it started working again but soon did the same thing so I left it until the next day.

Today I powered it on and only channel A gets power. I powered it off and on again and the sequence is a fast flash from DDT on both channels then channel A powers up but channel B does not. I am a tinkerer and would like a step by step to troubleshoot this issue. Any and all assistance is greatly appreciated.

7rrivera7
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Re: CS 800 Had Fading Channel B but Now has no power

Post by 7rrivera7 » Thu Jan 06, 2022 12:51 pm

Update: Today I powered on the amp and both channels came up and sounded fine. I left it playing and suddenly channel B's volume lowered, then raised, then lowered and continued. So today both channels are running but channel B's volume changes on it's own...

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Enzo
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Re: CS 800 Had Fading Channel B but Now has no power

Post by Enzo » Fri Jan 07, 2022 6:50 pm

OK, clean the input jacks.

Also, when it drops in volume, ball up your fist and whack the top of the amp. Does that make it come back for a time? Does the amo react to the whack in other ways?

Bartman
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Re: CS 800 Had Fading Channel B but Now has no power

Post by Bartman » Mon Jan 10, 2022 8:59 am

I also have a couple amps that the "whack" maintenance makes them come back to normal volume. I've tried cleaning and reseating all the internal cables but nothing seems to help. I glanced over the circuit board to see if there were any loose solder joints, but didn't see anything obvious. I will be interested to hear if others have come across this and found a solution.

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Enzo
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Re: CS 800 Had Fading Channel B but Now has no power

Post by Enzo » Mon Jan 10, 2022 9:11 pm

The whack is not intended as a repair, it is intended to expose loose connections. If the amp reacts, then SOMETHING needs resoldering or otherwise attended to. Poor solder joints are not always visually evident.

Your symptom screams of poor contact somewhere. Have you put cleaner into any stereo/mono switches, any bridge mode switches, and in/out switches for anything?

Bartman
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Re: CS 800 Had Fading Channel B but Now has no power

Post by Bartman » Tue Jan 11, 2022 8:55 am

Yes, I've tried cleaning switches, wiggling internal cables while sending a signal through it, and I still can't find where the fault is. The amp will work fine for as long as the system is setup, but after packing and riding in the truck then getting out at the next gig, I usually have to whack it for sound to come back, but not always. The amp I'm currently having this issue with is a GPS1500 model. I've had the same issue with a couple other amps of the same model.

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Enzo
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Re: CS 800 Had Fading Channel B but Now has no power

Post by Enzo » Tue Jan 11, 2022 7:59 pm

Well then I get out my scope and trace the signal into the amp. Is it getting to the min board? Is it getting to the output devices? Is there continuity between the output devices and the speaker connections?

Your initial complaint was a CS800, now you report the same issue with GPS1500, and further a couple more units (not sure what models they are) Same problem with multiple amps of various models really suggest the problem could be external to the amp.

IN a sound check setting or in your shop, try connecting the suspect amp to some speakers, and connect a CD player directly to the amp inputs and let her play. Does it still do this?

Bartman
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Re: CS 800 Had Fading Channel B but Now has no power

Post by Bartman » Wed Jan 12, 2022 9:40 am

I'm not the original poster about a CS800, I just commented I have the same problem with another model amp. I've done all external troubleshooting, it is definitely inside the amp, not external cables or input jacks. Since it only happens occasionally and always starts working again when I give it a small whack, I haven't taken the time to dig deeper.

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Enzo
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Re: CS 800 Had Fading Channel B but Now has no power

Post by Enzo » Wed Jan 12, 2022 3:13 pm

Sorry, you are correct, I didn't look at poster identity there.

7rrivera7
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Re: CS 800 Had Fading Channel B but Now has no power

Post by 7rrivera7 » Fri Jan 21, 2022 11:52 am

I'm the original poster. The amp has not had the problem lately. I am waiting for it to happen to see if whacking the top makes a difference and I will post the results.

Thanks for all the replys!

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