Author Topic: LCD wrong viewing angle Sony Walkman (Read 2529 times)

dredd · « **on:** December 22, 2023, 01:08:27 am »

Hello.

I bought Sony Walkman to restore, WM-FX822. I still waiting on rubber band, but radio works. Now problem is, I can see LCD screen in good contrast only looking at it at 45 degrees down from vertical, and still good all the way down to 90 deg (when its on the table and I'm on the battery side). When i move up to vertical view (0 deg) it fades to nothing.

I tried feeding it from lab PSU at 1.5V, nothing changed.

I attached service manual, IC702 is LCD driver chip. Whats can be done here, please?

Thanks!

dredd · « **Reply #1 on:** December 22, 2023, 01:16:56 am »

There is numbers on IC702 pins on the diagram, I think its ref voltages, I'm yet to check it. But I suspect complex waveforms there, from what I read on multiplexed LCD drivers, ones with more than one Common pin from the glass (this has four, there is pins description table in the doco).

GLouie · « **Reply #2 on:** December 22, 2023, 06:46:38 am »

Just guessing, could there possibly be a polarizing film over the display that is backwards, or missing?

dredd · « **Reply #3 on:** December 22, 2023, 07:29:39 am »

Quote from: GLouie on December 22, 2023, 06:46:38 am

Just guessing, could there possibly be a polarizing film over the display that is backwards, or missing?

Seems unlikely, how could this happen. I'm waiting on solder sucker and will lift the pcb tomorrow. There is "zebra strip", conductive rubber thing inside LCD assembly, I plan to open the assembly.

dredd · « **Reply #4 on:** December 24, 2023, 05:30:34 am »

Well, cleaning the conductive rubber strip inside LCD assy did not help

R.J. · « **Reply #5 on:** December 26, 2023, 11:17:53 am »

Does the walkman react on any button?

Please check C701 in the reset circuit and the other components around.

dredd · « **Reply #6 on:** April 17, 2024, 01:31:49 pm »

Quote from: R.J. on December 26, 2023, 11:17:53 am

Does the walkman react on any button?
Please check C701 in the reset circuit and the other components around.

Yes, Walkman if fully operational. Will do C701! Sorry for long delay, I used email I don't check, changed now

R.J. · « **Reply #7 on:** April 18, 2024, 09:24:37 pm »

The display is directly driven by IC702.
This is a microprocessor and need a oscillator to operate so also check R724 (470k) or the pins with an oscilloscope.There has to be a smal signal (sinus/square) on both sides of this resistor.
The reset signal from Q701 (collector) should be 0V and on pin 27 of IC702

dredd · « **Reply #8 on:** May 24, 2024, 02:20:16 am »

Quote from: R.J. on December 26, 2023, 11:17:53 am

Please check C701 in the reset circuit and the other components around.

C701 measured 2.21uF, spot on to nominal 2.2uF.
R724 also good, 445kOhm, nominal is 470kOhm.
Firing up my oscilloscope now

dredd · « **Reply #9 on:** May 24, 2024, 03:08:33 am »

Quote from: R.J. on December 26, 2023, 11:17:53 am

Please check C701 in the reset circuit and the other components around.

But voltages on Q709 are off!
1.45V instead of 1.3V on left side pin (Collector)
1.50V instead of 1.3V on right side top pin (Emitter)
0.9V instead of 0.7V on right side bottom pin (Base)

EDIT: Sorry, false alarm. It depends on power supply voltage. I set PSU to 1.3V and now Q709 reads:
1.3V on left side pin (Collector)
1.25V instead of 1.3V on right side top pin (Emitter)
0.7V on right side bottom pin (Base)

OK on Q701 left side pin (collector) = 0V
Not OK on Q701 right side bottom pin (Base). Reads 1.22V instead of 1.3V.

Also IC701 pins read wrong ... :
pin 48 = -0.23V
pin 47 = -0.23V
pin 46 = -1.75V
pin 45 = -0.73V

dredd · « **Reply #10 on:** May 24, 2024, 03:40:58 am »

Scope at R724 bottom (IC702 pin 39). PSU is at 1.30V

Scope at R724 top (IC702 pin 38)

Two together (I'm a scope master now :)

BTW, touching the top of R724 with scope probe changes waveform and lowers oscillator frequency for some reason ...

dredd · « **Reply #11 on:** May 24, 2024, 06:01:12 am »

My BM786 multimeter cannot measure the CB701 - the package with four 0.1uF caps in it. It connects to IC702 pins 44-46 and 40.
BM786 fails measuring any of the four caps, just gets stuck showing a dot.

Maybe this is it?

Haenk · « **Reply #12 on:** May 24, 2024, 06:58:27 am »

Before dissecting the machine, did you try with another polarizer?
The foils can fail (due to UV light, aka sunlight, but maybe even just age).
Any polarizer (that is not circular) will do, maybe rip it off another LCD display.

dredd · « **Reply #13 on:** May 24, 2024, 07:28:01 am »

It is kind of cumbersome opening lcd again, maybe i will.

jzx · « **Reply #14 on:** May 24, 2024, 06:15:19 pm »

Hello, this is my first post, so be patient, because my english is bad.
I am repliying to this post because once i have seen something similar, not with this model, but with a clock.
Check the capacitors on pins 41, 42 and 43, because this seems part of a voltage doubler. In my case, a capacitor was broken (short) and the lcd worked as if the battery was old, little contrast.
You can use the scope on these capacitors and post the pictures.

The capacitors C8701 are connected to several pins named "VL3", "VL2" etc, posibily decopling the lcd voltages, use the scope to measure the voltage. Check the resistance to see if they are shorted, but is dificult to measure the capacitance in circut, if some voltage is present, the measurement fails.

dredd · « **Reply #15 on:** May 25, 2024, 07:46:22 am »

Unsoldered CB701 and of couse it measures right

110, 110, 110 and 95nF
Now Im shopping for microscope to put it back. What are the good ones? AmScope double boom arm costs a kidney.

EDIT: Ordered AmScope SE400-Z, $450, cancelled it and got noname stereo one, used from eBay. It has 10xWF eyepieces and 2x and 4x detachable objectives. I need to find 0.5x or 0.75x barlow lens to replace the 2x one.

dredd · « **Reply #16 on:** May 31, 2024, 06:48:17 am »

Quote from: Haenk on May 24, 2024, 06:58:27 am

Before dissecting the machine, did you try with another polarizer?
The foils can fail (due to UV light, aka sunlight, but maybe even just age).
Any polarizer (that is not circular) will do, maybe rip it off another LCD display.

Well, now I can use hot air and solder paste, new superpower :). I soldered new CB701 back, no change.
Bought polarizer film, removed top polarizer, it was glued on. Tried new one - no change. Not a proper test, I did not cut the sheet and was just rotating it above display.
There is bottom polarizer too, I suspect, together with mirror foil, Im debating should I remove it too, because the voltages on IC702 were not right, polarizer might not be the reason.

jzx · « **Reply #17 on:** May 31, 2024, 01:41:17 pm »

Have you checked C710 and C711? Check with the scope, they posibily are part of a voltage pump.

dredd · « **Reply #18 on:** June 09, 2024, 07:28:36 am »

Quote from: jzx on May 31, 2024, 01:41:17 pm

Have you checked C710 and C711? Check with the scope, they posibily are part of a voltage pump.

C710 = 0.13 uF (0.1uF in specs)
C711 = 0.14 uF (0.1uF in specs) both are kinda OK.

Whats not OK is voltages on them. IC702:
pin 41 = +0.78V (+1V on diagram)
pin 42 = -0.24V (0V on diagram)
pin 43 = -1.25V (-1V on diagram)

Something seems to be off...

jzx · « **Reply #19 on:** June 10, 2024, 03:06:16 pm »

If you have a negative voltage, the charge pump must work. Is strange, because you have aprox the correct peak to peak V, so the contrast would be correct or at least not too bad. Can you measure the signals on the lcd with the scope?


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Author Topic: LCD wrong viewing angle Sony Walkman (Read 2529 times)

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