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

resistors often act as fuses ..some are in fact called fuse resistors . they are generally a different colour to the others and stood off the board a bit .
 
See those 3 transistors on heatsinks? How do their solder connections look? It is not uncommon for those to have bad solder connections due to the heat they produce. Hot / cold cycles causes solder to crack. Good solder looks shiny. Bad solder looks grey. Sometimes you can see rings where it has cracked. Google "Cold solder joint" and look at pictures.
 
redk9258 said:
See those 3 transistors on heatsinks? How do their solder connections look? It is not uncommon for those to have bad solder connections due to the heat they produce. Hot / cold cycles causes solder to crack. Good solder looks shiny. Bad solder looks grey. Sometimes you can see rings where it has cracked. Google "Cold solder joint" and look at pictures.
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They all have looked fine from the beginning. I reflowed them just in case though. And the middle transistor is the one I thought went bad when I shorted the board.
 
I found another d1265a that is acting strange. Diode testing with ground on base says that the E and C are open but positive on B shows that C is 900 and E is 1500 while on the other one they were both 600. I'm leaving it desoldered until I see what one or any of you say.

Btw it's q854
 
Service manual is available free at https://elektrotanya.com/jvc_r_x400_x500b.pdf/download.html
Wait for the "get manual" link to appear below, then click on the link.
R-X400 and R-X500B share the same manual.
Q806 is the negative regulator. You should have -15V on the emitter and -40V on the collector and -15.6 on the base. Wrap the meter probe with electrical tape so only the very tip is exposed. This will help prevent shorting things out when you slip with the probe.
 
dr*audio said:
Service manual is available free at https://elektrotanya.com/jvc_r_x400_x500b.pdf/download.html
Wait for the "get manual" link to appear below, then click on the link.
R-X400 and R-X500B share the same manual.
Q806 is the negative regulator. You should have -15V on the emitter and -40V on the collector and -15.6 on the base. Wrap the meter probe with electrical tape so only the very tip is exposed. This will help prevent shorting things out when you slip with the probe.
Click to expand...
I cannot find q806. What board is it on?
 
My guess is you are going to see very low voltage on the emitter and a larger voltage on the collector and the transistor will be very hot. If this is so, with the power off, measure the resistance between the emitter and ground and the base and ground. I bet you will measure a low resistance from the emitter to ground. Why do I know this? These digital receivers use special switching ICs to switch the input signals instead of reliable mechanical switches like in the old days. The switching ICs have FETs in them that are very sensitive to ESD and powerline spikes and they use + and - 15V supplies. When they go bad they take out at least one of those supplies. Here's the bad news. These receivers have many of these switching ICs and usually more than one goes bad. If there is a short from -15V to ground, start de-soldering the switching ICs one by one until the short is gone. If you can still get the ICs they are not cheap. The ones in question are LC4966 and these are junk. They go bad all the time.
 
dr*audio said:
My guess is you are going to see very low voltage on the emitter and a larger voltage on the collector and the transistor will be very hot. If this is so, with the power off, measure the resistance between the emitter and ground and the base and ground. I bet you will measure a low resistance from the emitter to ground. Why do I know this? These digital receivers use special switching ICs to switch the input signals instead of reliable mechanical switches like in the old days. The switching ICs have FETs in them that are very sensitive to ESD and powerline spikes and they use + and - 15V supplies. When they go bad they take out at least one of those supplies. Here's the bad news. These receivers have many of these switching ICs and usually more than one goes bad. If there is a short from -15V to ground, start de-soldering the switching ICs one by one until the short is gone. If you can still get the ICs they are not cheap. The ones in question are LC4966 and these are junk. They go bad all the time.
Click to expand...
There is not LC4966 on this reciever. There is an LC7520, this might do the same thing.

Just looked it up, it is the volume control and EQ chip. This may actually be bad though because when I tested with headphones volume control did not work.
 
dr*audio said:
My guess is you are going to see very low voltage on the emitter and a larger voltage on the collector and the transistor will be very hot. If this is so, with the power off, measure the resistance between the emitter and ground and the base and ground. I bet you will measure a low resistance from the emitter to ground. Why do I know this? These digital receivers use special switching ICs to switch the input signals instead of reliable mechanical switches like in the old days. The switching ICs have FETs in them that are very sensitive to ESD and powerline spikes and they use + and - 15V supplies. When they go bad they take out at least one of those supplies. Here's the bad news. These receivers have many of these switching ICs and usually more than one goes bad. If there is a short from -15V to ground, start de-soldering the switching ICs one by one until the short is gone. If you can still get the ICs they are not cheap. The ones in question are LC4966 and these are junk. They go bad all the time.
Click to expand...
i have come across this myself a few times now . it can happen by swapping rca input cables with unit powered on .. i remember one was a 28 pin chip . all i do is disconnect the power supply pins then jumper the correct pins to switch an input and see what happens . others have a few chips for switching and can take longer to find the bad ones .. what i have found when these chips go bad is the signal will bleed into other inputs from the one selected . sometimes finding one that makes the unit work ok .
 
petehall347 said:
i have come across this myself a few times now . it can happen by swapping rca input cables with unit powered on .. i remember one was a 28 pin chip . all i do is disconnect the power supply pins then jumper the correct pins to switch an input and see what happens . others have a few chips for switching and can take longer to find the bad ones .. what i have found when these chips go bad is the signal will bleed into other inputs from the one selected . sometimes finding one that makes the unit work ok .
Click to expand...
I still don't understand what chip I'm looking for or how it pretains to figuring out what broke when I shorted this board.
 
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