CX-830

nazrin

New Member
I have a preamp CX-830 which controls the MX-830

I've had two amps connected to this preamp and have the sample problem

the sound is completely turned off for about 4-6 sec then back on.....does it randomly, 4 times in an hour or better.....like something warms up then the sound goes off for this time then back on

I am certain it is the preamp doing it......What should I look for or replace within the PCB to fix this problem?
 
Whats your geographical area ? The problem could be a number of things. Need a little more info. Does it matter what input is selected ? What inputs are you using ?. It could just be a cold solder connection. I'm assuming this occurs in both channels. Common circuit to both channels is the power supply.
 
Whats your geographical area ? The problem could be a number of things. Need a little more info. Does it matter what input is selected ? What inputs are you using ?. It could just be a cold solder connection. I'm assuming this occurs in both channels. Common circuit to both channels is the power supply.
It cuts off sound completely, yes both channels, and it does not matter which input I select. I use the Rec out knob as I have an EQ and mainly us CD,tuner, LD

The power stays on while both channels cut out....
Oh, thanks for your reply, I’m in central maine
 
Have a close look at Q72 and Q76 solder connections. These two are on the two large heatsinks.
 
Yes, I can follow a schematic to some degree, where can I find a schematic to look for Q72 and Q76

also, I can say no crackling during this on/off sound, very clean on/off.....wouldn't a bad solder connection have some noise associated with it?

I'd love to figure this out, it's been doing it for 4 years now
 
Have you eliminated the EQ as a possible culprit? Had an EQ in a system that exhibited similar symptoms, drove me crazy .

A couple of cold solder joints in the EQ were touched up and solved the problem. Just a possibility...
 
So I turned off the EQ-630, with no EQ, after an hour it cut out three times in the next 45 mins....so it looks to be the CX-830
 
The cs-830 has a mute circuit, maybe malfunctioning? Need to take a closer look.
Is the off/mute period always about the same 4-6 seconds?
 
Probably a power supply problem to one of the opamps which is shared between L&R channels.
Will try and get some test points.
 
This is going to be a bitch if it only acts up for a few seconds.
 
Common circuit to both channels is the power supply.

Probably a power supply problem to one of the opamps which is shared between L&R channels.
Will try and get some test points.
If its a transistor intermittently failing.. Its going to be pretty rough nailing down the " root cause"...
 
Have a close look at Q72 and Q76 solder connections. These two are on the two large heatsinks.
The opamps of interest are fed by Q72 & Q76. Have you checked the solder connections as per above. Google dry solder joints for pic's
 
Probable scenarios are,
- power supply intermittent failure due to bad solder joint or transistor
- intermittent opamp failure, much less likely.

Two basic techniques,
- monitor psu voltage
- monitor audio signal with probe to find out where it fails

The screen print from the service manual is not great.
Need to identify the +18 and -18Vdc voltage rails that feed the opamps.

With amp powered up normal, measure the dc voltage at jumpers J172,3,4 and J150
as per pic. I'm guessing that 2 of these will be +/-18Vdc (approx). Need to put
clips and set up 2 multimeters to monitor voltage.

The audio probe is slightly easier but less likely to find the fault.

The easiest solution is to check Q72, Q76 solder joints

This is going to be a bitch if it only acts up for a few seconds.
agree

CX830.JPG
 
Wow, thanks for this input and help. I have not opened the unit yet and yes, about 4-6 seconds.....

I was considering the mute circuit as it sounds that smooth, on/off sound

I was thinking the IR input was receiving a false signal or maybe the circuit was sending this signal internally
 
I was having the same issue, sometimes the audio was muting for 5 secs. Thanks to this tread I solved my issue. In fact it was some solder joins in this area (the transistor pin). So, I can confirm this fix. Thanks to all.
 
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