JVC AX-90V

Fredrik 1977

Super Member
hello ak:ers

im sitting here scratching my head with this unit. it works but has distortion on right channel.
im more into older amps so this is not my cup of tea. ic:s allover:) and some seriously inaccessible boards
all voltages looks pretty good except dc on right output 360mV
left out has a mere -25mV
amp only have idling current ajustments. am i looking at bad drivers here?

regards fredrik
 
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As far as i know in mid to late 80s jvc units, distortion in ONE channel is usuially caused somewhere in the pre amp circut from something like a bad cap.
 
I'd pull that pre-driver (ENG-004) PCB and have a look at the solder joints. I'll bet there are many cold solder joints on it. Apparently it is the same PCB (ENG-004) that is used in the RX-9V and RX-950V (and others). I've noticed on the one from a RX-950V that there are unused pads and places for additional components. This amp has 2 additional plugs and goes to a place between 25K Ohm and 75K Ohm resistors. The RX-950V uses a 100K Ohm resistor.
 
thanks all so far.

schematics i already have, i got the SM. but that schematic is pretty heavy reading:)

i have not pulled the pre driver board yet but from what i can see the soldering looks just fine. only some small signal stuff on there.
 
voltages on ENG-004 connector
1: 0V
2: 0V
3:0V
4: 0V
5: 0,3V
6: 0,9V
7: 1,5V
8: -67,7V
9: 67,7V
10: 2,3V
11: -2,37V
12: 0V

pin6 and 7 is very off! shold be the same as pin 10 and 11.

guess i have to pull that boad :D
 
wasnt easy getting the board out but i did. and i refloated the whole pcb and checked the transistors briefly.
put the board back. but still 350mv on right out.
 
IC751

pin/VDC
1: 1,65
2: 0,97
5: -1,7
6: 0
9: -1

IC752

1: 1,15
2: 1,15
5: 0,75
6: 0,33
9:1,15
 
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im currently trying to get the main amp pcb out of the unit but man! what a piece of S#¤T engineering!
probably will end up taking apart the whole unit before i get there.
if any one finds one of these amps broken, just leave it and go on with your life :), you will be much happier that way lol
 
found that Q857 Vreg is out of spec.

B -23V
C -38V
E -23V

i still have not managed to get the amp board out though. working on it.
 
yes but i get only partial access. i cant probe or solder the stuff i would like(Q752,754).

the pcb is much bigger than the hole in the chassis. so to speak.
 
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Ahhh. I think you will have to remove the front panel. In addition to the screws you know you have to remove, there is one screw in the mid section. It is shown in the SM.
 
front is allready off along with the "system" pcb that sits ontop of the main amp.

i did also remove the 2 psu pcbs when investigating why the Q857 regulator had a bad reading.
lots of that corrosive glue on the bottom psu pcb. ill look into that later, from what i can tell that vreg is powering the lamp assy (wich actually works):)
 
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Hello,
I have two of these JVC AX-90V units. One has the same issue as yours - right channel distorted output. The other unit does not power on completely anymore. I definitely do not know electronics so I was just wondering if anyone on here would be interested in these two units.
 
Hi!

update:
this project is put to sleep at the moment since this was probably the most boring unit to work on :D
sort of like working on a VHS recorder from 1990.
so once i clear out the bench i will start fixing some classic receivers again:)
 
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