Alpine V12 issues

[vincegironda]

Hi I have an MRV1507 with output issues on the bench,

the amp powers up and idle's fine,
with the input switch set to 1+2 mode it plays clean audio on both channels.

with the input switch set to stereo mode it only plays audio on the right channel and very low on the left, there's very low audio bridged.
Idle becomes erratic on bridged mode.

with the switch set to mono there's very low audio

I've already checked the amplifier board for dry joints and run solder on any suspect joints with no change.

any support with this appreciated
thanks

 

[Perry Babin]

Does audio intermittently change when you operate the switches and pots through their entire range?

 

[vincegironda]

Thanks Perry, I tried all the pots as you suggested and no change.
Adjusting the switch positions on the parametric and hp lp filter switches causes intermittent audio on the left channel. The audio cuts in and out like it's cycling. Pops the speaker a bit too.

 

[Perry Babin]

I'd try cleaning the switches before doing anything else. The popping could simply be the intermittent contacts or you could have excessive DC on an op-amp (probably just the contacts).

 

[vincegironda]

I've cleaned them with deoxit and now I have both channels working when the input selector switch is in stereo mode, mono mode and 1+2 no longer work.
could all the switches be bad?

 

[Perry Babin]

Did cleaning involve operating the switches through their range for about 50 times after flooding them with deoxit?

Switches that are not visibly damaged are rarely damaged where they cannot be cleaned.

 

[vincegironda]

I drowned the switches in deoxit and switched them hundreds of times, stripped and cleaned the eq and gain pots with deoxit and managed to get all the functions back except left channel in stereo mode.

I had a spares MRVF400 with the same 3 way switch so I swapped it out with the input mode switch and thoroughly deoxit cleaned it the same as the others, I still don't have the left channel on stereo mode?

I noticed one of the vias came away from the board when I desoldered the original switch, it doesn't appear to be connected to anywhere as I can't see any traces, could it be a multi layered circuit board and am I missing a connection?

 

[vincegironda]

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[Perry Babin]

Service manual, eprom result list | Elektrotanya

 

[vincegironda]

Thanks Perry, I tried a different electrical contact cleaner and it appears to have done the job. Surprising considering its a 5th of the price of deoxit.

 

[Perry Babin]

That's not surprising. The lowly WD-40 has been used successfully to clean contacts. I don't recommend it because it stinks and it's not seen as acceptable by many techs.

 

[vincegironda]

Thanks Perry,

on another note can you suggest a second hand scope please?

 

[Perry Babin]

I know this is a waste of time typing this but I'd suggest an older CRT based scope due to display quality.

Buy what's available in your budget. I don't have any suggestions for someone buying an LCD based scope.

If you can work without the fancy digital readouts (few getting into this can) I'd recommend an old Tektronix 465B or many of the older 2200 series Tek scopes. Hitachi, Kenwood, BK precision all make very usable scopes and can often be purchased for about $150 used.

If you're going to buy off of ebay, email me the scopes that you're interested in.

As a minimum, you should only consider scopes that have a sharp, bright trance and those who have a locked waveform on the display. If you can find something locally that you can try before buying, that's a bonus.

Probes are dirt cheap. The ones you can buy on ebay for $5 each 4/$20 work perfectly fine for car audio.

 

[vincegironda]

Thanks for taking the time to reply Perry, I'll take your suggestions on board and let you know if I find one before purchase.