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JVC R-X400 no output and LCD doing some weird things

ExcitableOne

ExcitableOne

Active Member
So I bought an untested JVC R-X400 on eBay kind of knowing this would happen. As of right now I'm getting no output, one of the fuse lamps is burnt out, but I know how to replace that. The spectrum analyzer is peaking at all but one frequency, and the display at that part I'm assuming displays the source, volume, and sea settings is blank. I found a zener that looks a bit not right, but I have a feeling it's actually fine. Output transistors are alright. All visible caps appear to be just fine. Where should I go from here?
 
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I'd be checking for dry solder joints for the display issues. Does this unit have main in / pre-out jumpers?

Connect the Rec Out to another amp and see if the preamp section works.
 
redk9258 said:
I'd be checking for dry solder joints for the display issues. Does this unit have main in / pre-out jumpers?
Click to expand...
Like test points for the input and preamp? I can check, there are a lot of jumpers all over the board that I've been meaning to look into
 
redk9258 said:
I'd be checking for dry solder joints for the display issues. Does this unit have main in / pre-out jumpers?

Connect the Rec Out to another amp and see if the preamp section works.
Click to expand...
Okay I read that again now that I'm more awake and I understand much more, I'll do both of these things after I get home from school.
 
redk9258 said:
I'd be checking for dry solder joints for the display issues. Does this unit have main in / pre-out jumpers?

Connect the Rec Out to another amp and see if the preamp section works.
Click to expand...
Output kid of works from amp, it's highly distorted and the actual quality is bad. Output from headphone jack is the same way. Trying to locate the preamp now since everything is labeled.
 
i am thinking the power supply has issues . always best to start there as nothing will work properly with incorrect voltage .plus it can find shorts further down the line .
 
In my experience highly distorted sound could mean a bad cap in the pre amp, or a opened ground in the amplifier section.
 
petehall347 said:
i am thinking the power supply has issues . always best to start there as nothing will work properly with incorrect voltage .plus it can find shorts further down the line .
Click to expand...
While I was doing this I managed to miss arrange the ribbon cables. Therefore I put -90v through the +5v rail, most likely killing the smd chips that are no longer made for the display. I figured this out by taking this cable out and shocking myself with it and wondering how 5v could shock me. I also shorted the ground to the pin next to it and it sparked and melted the wire and the problem on my multimeter. I'm glad I didn't touch that one.
 
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