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

redk9258 said:
Are you sure you don't have a tape monitor engaged? There are two and if either is engaged without a tape deck (or other) connected, then no sound.
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Even if I did I wouldn't know because that part of the LCD doesn't work right now, I received it that way. And I don't think I do because I got sound out of it already, just it crackled really loudly at a really high pitch worth no rhyme or reason, and the actual audio was incredibly quiet and distorted.
 
redk9258 said:
Are you sure you don't have a tape monitor engaged? There are two and if either is engaged without a tape deck (or other) connected, then no sound.
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Yes, I got sound out of it once but it was really crackly and the actual audio was incredibly quiet and distorted. That part of the LCD currently doesn't work though for whatever reason. I got it this way so not my fault

Of course that other one did work and just didn't want to show up until now. Just disregard this.
 
In order to fix the lcd display, you must

1. Replace the fuse lamps.
2 replace the diodes if they are shorted ( these diodes are most likley on the same board that the fuse lamps mount to.
3 fix any cold solder joints on the board with the diodes and mounted fuse lamps, and any cold solder joints where the actuall lcd is mounted, (there is going to be a line of about 60 small joints that connect the lcd to the circut board.

If part of the display was out for a while but then decided to turn on then i would guess that cold solder joints on the diode/fuse lamp board are the problem.
 
ELzekio said:
In order to fix the lcd display, you must

1. Replace the fuse lamps.
2 replace the diodes if they are shorted ( these diodes are most likley on the same board that the fuse lamps mount to.
3 fix any cold solder joints on the board with the diodes and mounted fuse lamps, and any cold solder joints where the actuall lcd is mounted, (there is going to be a line of about 60 small joints that connect the lcd to the circut board.

If part of the display was out for a while but then decided to turn on then i would guess that cold solder joints on the diode/fuse lamp board are the problem.
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I'm going to order zeners and lamps soon.

All of the solder joints look alright on the LCD but I'll remelt them when I get a chance.
 
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redk9258 said:
We need to get a signal either from the preamp section or inject a signal into the amp section to see where you are not getting sound. Maybe a couple of things to check first...
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I tested the preamp, it is distorted not as much, normal volume, none of the crackling I was getting off the amp. The only reason I can think of for this is a bad cap or one of the chips doing weird things.
 
Don't focus on 'chips doing weird things'. IC's (chips) usually either work or don't. Focus on cold solder joints. Look closely at larger transistors with heatsinks used as voltage regulators. It is not uncommon for them to run hot enough to unsolder themselves from a PCB.
 
ExcitableOne said:
Alright I will test in a second, and what else should I check on the preamp?
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If you have (a) shorted zener diode(s) near the fuse lamps, I would either unplug that PCB or wait until you have that fixed before troubleshooting the sound. To check the preamp section properly, you need an oscilloscope. If you can run the REC OUT into another amp, headphone amp, tape deck that has a headphone jack, etc., you can listen to verify the sound is clear or distorted.
 
redk9258 said:
If you have (a) shorted zener diode(s) near the fuse lamps, I would either unplug that PCB or wait until you have that fixed before troubleshooting the sound. To check the preamp section properly, you need an oscilloscope. If you can run the REC OUT into another amp, headphone amp, tape deck that has a headphone jack, etc., you can listen to verify the sound is clear or distorted.
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I have done that, and I know it is distorted. And I've had that pcb unplugged since I noticed the zeners were messed up. I have new ones and new lamps ordered.
 
ExcitableOne said:
-23 to -29 milivolts from each side of both resistors. I do not think this is what it should be.
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That is pretty good. At least it is not up in the 100's of mV or volts!
There are a couple of other things that could really mess with the speaker sound output.... The relay has oxidized / dirty contacts, and the speaker switches themselves have oxidized / dirty contacts. This is common on all amps with speaker switches and protection relays.
 
redk9258 said:
That is pretty good. At least it is not up in the 100's of mV or volts!
There are a couple of other things that could really mess with the speaker sound output.... The relay has oxidized / dirty contacts, and the speaker switches themselves have oxidized / dirty contacts. This is common on all amps with speaker switches and protection relays.
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So should I invest in some dexoit and buy a new relay? And I'll check out the x500s preamp and see if it's the same. Since I don't have a scope should I just do a recap or something?

Just popped the top of the relay, the contacts are pretty messed up. Should I replace or use dexoit when I can afford some?
 
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Picture of the relay contacts, not the best but the best I got
 

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You can try contact cleaner applied to a business card or strip of paper. Put it between the contacts, close the contacts lightly, pull the paper through. Keep going until the paper is clean. Have you tried the headphone jack?

The preamp board may be slightly different. There is usually a letter at the end of the number that indicates how the board is 'stuffed'. Different locations, models etc.
 
redk9258 said:
You can try contact cleaner applied to a business card or strip of paper. Put it between the contacts, close the contacts lightly, pull the paper through. Kepp going until the paper is clean. Have you tried the headphone jack?
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Yes, it's off the amp. I think there are resistors to drop the voltage and limit current. It sounded exactly like the amp when I tried it, not the preamp. And I'll get some dexoit then. The d5 is what I want, right?
 
What fuse lamps / zener diodes did you order? There is a service bulletin posted in another thread for the later models that use the same setup. When a lamp burns out too much current goes through the diode and causes it to short. This causes problems with burned PCBs, resistors etc. Your unit was built with 12V 500mW Zener diodes and 12V 150Ma fuse lamps. You should use 12V 1000mW Zeners and 12V 150mA fuse lamps for replacements.

I think Deoxit D5 is good for switches. Don't use it on slide controls though. Only F5 fader lube.

I wouldn't but the relay yet. Not until you can get undistorted sound from the preamp. When you decide to, I think I might know a number that is available now. Post the number of the original part though.

R-X500 fuse lamps.PNG
 
redk9258 said:
What fuse lamps / zener diodes did you order? There is a service bulletin posted in another thread for the later models that use the same setup. When a lamp burns out too much current goes through the diode and causes it to short. This causes problems with burned PCBs, resistors etc. Your unit was built with 12V 500mW Zener diodes and 12V 150Ma fuse lamps. You should use 12V 1000mW Zeners and 12V 150mA fuse lamps for replacements.

I think Deoxit D5 is good for switches. Don't use it on slide controls though. Only F5 fader lube.

I wouldn't but the relay yet. Not until you can get undistorted sound from the preamp. When you decide to, I think I might know a number that is available now. Post the number of the original part though.

View attachment 1039436
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I bought 1w zeners, didn't check the current on the lamps though. I got ones with 5050 LEDs on it though. While it is meant for cars it was one of the only 12v ones I found. And do you want the number for the relay?
 
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