Front board assembly replacement
Looking for a new front board assembly or advice about fixing the display on a pioneer vsx321 stereo receiver. LCD display appears to have blown.
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Hi
Here’s the service manual for the receiver.
On p.39 it shows the start of the dis-assembly procedure. The front board assembly section starts on p.41.
I only found one supplier when searching online for the front board assembly part # 7028071131010-IL. but not sure if they have the part or not as you have to sign in.
On p.77 is the schematic of the front assembly which may be of some help.
I’ve attached an image to show just a small section and have highlighted some capacitors connected to the LCD circuit that may be worth looking at. Not saying that they are the problem though. (see red boxes in image)
I’m wondering if backlighting for the display is actually some sort of fluorescent light as the display is designated FLT701 and the power for it seems to come directly from the power board, an inverter circuit perhaps- I didn’t look, (see green arrows in image). The part number for the display is K530126600010-IL but I' haven’t found any when searching using the part number. You may have better luck
(click on image to enlarge for better viewing)
Hopefully a start.
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I am having the same issue. I found someone on eBay selling a front board assembly for another model and I replaced it, but I am still having the issue. The LCD is on and a very, very faint light can be seen. see attached picture.
The capacitors seemed ok, but I am not able to figure out what voltage the display should be receiving. I am reading around 0.98V on all of the leads that you had highlighted. but that seems very low to me. I am studying electrical engineering and this is a good learning opportunity for me and the receiver works perfectly other than that. the other display broke when I was removing it when something from my desk fell on it. here are pictures of it up close for clues. It definitely seems to have been a gas type of LCD as the whole thing was glass with space in the center for gas.
As you can see in this last picture that charred circle in the bottom left was already there before the display broke, I’m thinking something might have overvoltaged the display, but it seems the new one also has this circle in the same sot so maybe not? Hopefully, this is helpful in finding the problem, thanks for any advice or help, and feel free to ask for more measurements or readings of parts of the circuit.
edit: I also just checked and the cpu 3.3V pin is in fact getting 3.3V
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Hi,
Before the advent of LED backlighting for LCD displays, CCFL tubes (cold cathode fluorescent lamps) were used to light the screen. Sometimes they were able to be individually replaced in the display assembly when they failed (just like standard household fluorescent tubes - get darker with age and then fail) but sometimes they were permanently fixed and the only way was to replace the complete display assembly. You can see the end of the CCFL sticking out in the 2nd last image that you posted
These required a high AC voltage to operate.
As can been seen in the schematic image in my answer the two capacitors C718 & C719 both have a voltage rating of 100V.
This is not to say that 100V AC is applied to the CCFL tubes but it gives an idea what the max voltage it might be as the DC voltage rating on the capacitor is 1.4X the AC voltage value (i.e ~70V AC rms = 100V DC)
Looking at the schematic in the service manual, the voltage is sourced from the mains transformer board.
Unfortunately it isn't very detailed as to precisely where but if you follow CN701 pins 1, 2 & 3 you can trace back to where they connect.
Hey, I followed the wires and they connect directly to the transformer, I am now reading (with the proper ac ground)
FL1= 72-88V
FLCT= 72-88V
FL2= 72-88V
and these values go directly to the display pins.
I think both these displays are just toast, even though that seems unlikely.
@ paul thillier
Did you measure between FL1 and FL2 and between FL1 and FLCT and also FL2 and FLCT?
There should be 0.5x the voltage between the centre tap connection (FLCT) and each of the two outer connections of the transformer FL1 & FL2.
CCFLs and LCD displays in general have fragile internal connections so perhaps it is not surprising that they both may not work
