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old car stereo LCD backlight

Delta Prime

Jul 29, 2020
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Further inspection is needed

photo_1688116090650.png

Looks like someone has already been inside this unit, looks like an unsuccessful repair. solder shorts along with discontinuities or breaks in the traces.
IC901 refer to schematic.
Specialized equipment needed for repair hot air gun & flux solder paste.
Skill set is advanced
I am hoping this is a case of lights and shadows . Needle tipped probes would be needed with a very light steady hand to make an resistance measurement from the pins themselves following the traces until they terminate to "vias" tiny round holes that go through the circuit board and are covered with green conformal Coating, take a razor blade or Emery cloth and scratch off the coating lightly on the vias that is where you would make your measurement from the PIN of the IC to the via. In this photo below there's a via located
in-between the bottom two arrows outside of the red circle and the Via looks rather robust.
photo_1688115190507.png

Further inspection is needed... Solder splatter,
Oxidation, corrosion.
photo_1688115850761.png
 
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straw_man

Jul 1, 2023
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I am half-trying to resolve a dodgy backlight on a DAB radio LCD display. I have little idea of these matters, but I noticed this recently about a car radio successful repair of similar symptoms:
I prefer your car to a Jag most days!
 

Delta Prime

Jul 29, 2020
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I have little idea of these matters, but I noticed this recently about a car radio successful repair of similar symptoms:
That's why when one has a little idea they pay someone else for profit to fix it. For me to even see it touch it 60 bucks U. S.
But that is an option. Here you get proper guidance for free! Which is also an option.
 

Delta Prime

Jul 29, 2020
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The link he posted was for profit
Which is an option.
Here with you guys I'm a volunteer and he is definitely getting his money's worth.( See how I left myself open) I am three steps ahead of you guys I'm setting you up. The old switcheroo...
 

straw_man

Jul 1, 2023
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That's why when one has a little idea they pay someone else for profit to fix it. For me to even see it touch it 60 bucks U. S.
But that is an option. Here you get proper guidance for free! Which is also an option.

The link he posted was for profit
Which is an option.
Here with you guys I'm a volunteer and he is definitely getting his money's worth.( See how I left myself open) I am three steps ahead of you guys I'm setting you up. The old switcheroo...
"The link he posted was for profit" I presume "he" is me. The link I gave is a detailed description of a repair. There is a short comment offering repair for reward. You are misrepresenting my post.

I don't know why you feel the need to be snippy about me posting the link whilst admitting I'm not knowledgeable in this area. It's quite possible for the uninformed to see a reference that is still useful. If it isn't useful, a short, clear statement to that effect and your reasoning would be sufficient.

Maybe you feel some ownership of this thread given your inputs, but it is open for others to contribute. Good luck with the "60 bucks" to "touch it", although I don't see the relevance to my message or the thread.
 

73's de Edd

Aug 21, 2015
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Sir die.nard . . . . . .

I wuz a gonna . . . . . in keeping along with the same sidetracking of semantics . . . as this thread was earlier evolving into.

Along with the EXTREME tangential in the troubleshooting erroneous direction now developing.

I say again . . . I WUZ A GONNA . . . . take the limited service info provided, and start you on a circuit flow path of the car battery to the failed display.

FIRSTLY . . . I am "consuming" that the radio is playing and changing stations . . . . . your display just WONT let you see what station is being tuned into ?

Consulting my SUPER MARKUP . . . . . BAMMMMMMMMMMM ! ! ! . . . . . . . here it is !
( Ye HUMONGOUS olde tyme markup . . . . . . both, in its size and content . . . .)

1688358203045.png

Also being co-hosted as :

After seeing the clarity of our sites provided image . . . DO USE the above link . . . . as you will need its provided EXTRA definition !


I saw your urgent dilemma and initially thought of drawing up a custom related mark-up that would take you on a sequential path from car battery, right on to the now dormant LCD display.
Well I got along fine, as you can see in my then created central area partial schematic, with my occasional zipping up topside to fill in like congruent reference points on your related panel photo, you know, the one with the flare out light reflection, in its top left quadrant.
Now, no where on its silk screened marking do I see any PL901 or PL902, so I see that the supplied reference 4 page schematic is insufficient and I then go on and find the FULL 58 pages. There, I'm interested in the X-ray depiction of the foil pattern of the display board.
My bottom left corner display is a condensed left and half portion . . . . with center area cropped out . . . of our point of interest, extreme right and left ends now being shown.
There you see PL901 and PL 902 marked in and ALSO the gold nugget words, being just underneath them . . . . . ( LCD BACK LIGHT ) . . . . . that says it all . . . . a mere two mini incandescent lamps are creating the LCD background lighting !
Further consulting PL901 and 901 in the parts supply list elsewhere, repeats that info with their Sony part numbers . . . .

Sony bare wire leaded back light incandescent lamp
1-517-633-11 and ( 1-517-633-21 is its new number )
Checking Sony parts stocking . . . . CURRENTLY ON FACTORY BACK ORDER
Pricing . . . . .@ $13.95 EACH ! . . . . . . BABYCAKES . . . .

WHUT ! ! ! ! you now done only went and paid $25 for the WHOLE . . . RAY-DEE-OO, speakers and wiring harness . . . with its fuse. ?

NOT TO WORRY ! Ive encountered these mini sized "grain of wheat / rice lamps " before, and in many voltage ranges.
Pulling out my GOGGLES and doing a GOOGLE search, I find multiple sources but all are not of ANY help on the lamps specs, like voltages and physical dimensions.
EXCEPT . . . .this one . . . .


With:
3V-3mm Grain of Wheat clear lamps . . . . . . . . ~$3.31 for 10x parts cost including postage with . . . ~ 15 day delivery.
So o o o o o o o o o o o o . . . . . . is it possible that the car that your "new" radio was in, hit a 6 inch pothole and jarred one pilot lite filament open ?

Back to the technical evaluation now, I have made all pilot lite / back lite info in VIOLET referencing.
Looking at the central schematic you see the start of power routing to the display starting at the RED arrow at the car battery and following a RED arrow path until it reaches GRAY CIRCLE at the collector of a Q631 regulator transistor that takes the base referencing voltage from a lower D631 which is being a 12.1V 1 watt Zener diode and outputs an ~ 11.5 regulated output voltage at its emitter, after subjection to internal C-E junction voltage drop.
Further follow the RED arrow path thru 4 series voltage dropping / current limiting resistors, then further on down the RED arrow path until reaching the GREEN CIRCLE where the lower D557 which is a 6.2 V 1 watt zener, which further pulls down that supply voltage to a 6.2 VDC.
Keep following the RED arrow path until that reaches the VIOLET referenced PL901 and 902 back lite lamps . The two lamps are series wired and that should halve the supply voltage across the pair and have a resultant ~ 3.1 VDC across each lamp.
I assigned A- B- C- D to the four lamp leads, to mark up related referencing on the schematic / drawings / photo.
Looking at the references extreme bottom left quarter quadrants SONY X ray photo . . . . .to our interest now.
Using your top photo referencing both ends are now flopped horizontally on the X ray view, so either use the boards four corners, having three PALE BLUE MARK UP corners being notched off and one corner having an intact corner . . . RED BOX referenced PALE BLUE MARK UP.
OR just remember that the PL902 lamp will have the CNP 901 connector, being very near to it . . .ORANGE line and BOX referencing.
Stop at that area and see that PL902 lamp has its left A connection lead soldered into the board ground plane.
The PL902 lamp B lead, I have marked in, is connecting to a VIOLET lines thru board VIA that connects to the other side of the circuit board to , then travel across and all the way over to another VIA that connects to C connection of the other PL901.
The lamps D connection then can be seen wired directly into the B+ 6.2 VDC pad.

NOW . . . . . . time for you to do some analysis on that pulled board.
If you will take your metering medium in hand . . . preset to ohms function . . . low range ( unless auto ranging).
Your lamp choice now, but stab a meter probe pair into CD and then AB to see where the low ohms reading is being.
The low ohms reading, is being on your still usable lamp and the high reading lamp, is just being stray loops higher resistance.
Considering you find that exact situation do a fixed memory lock on the good lamps position.
Next we need to find out the $13.95 PLUS shipping+ handling+ tax . . . . .on the SONY lamp
. . . .VERSUS . . . . .
the 25 cent lamp. . . .YEAAAAAAAAA ! *****
You need to series connect two good 1 1/2 V dry cells to end up with 3 V coming out of two leads. Next you solder tack the two tinned wire leads to the respective solder dots of the good lamp. Polarity being typically irrelevant . . . .BUT . . . ..the unknown aspect of tied in solid state devices loading effects, would prefer that you have one lamp lead directly connected to ground plane and the other lamp lead has one connection to B+.
Therefore you would have PL901 " lead " D being connected to battery positive and , C to battery negative.
Or the other situation is with PL902 lamp, where lamp wire A would receive batt neg and lamp wire B would go to batt +.
You do have a TRANSMISSIVE type of LCD display element being used and I am unsure if you power up that one lamp on 3 V if that then NON POWERED display panel will exhibit a blocked out / Black display or if it will let full light from the, now only half lit back light display, to shine back light illumination thru it.
You find out and show and tell us.
If there is adequate illumination . . . . . evaluate the degree of side to side lack of the other sides lamps illumination.
E.G. does it seem that you WOULD be able to read the display, but tolerate the imbalanced half lighting effect

FIO . . . . I am expecting the now hidden pair of lamps to nestle into and illuminate into a 1/8--1/4 in thick Plexiglass / Lucite sheet that functions as a " light pipe " for its central illumination to pass forward and pass thru the LCD display.
Mid right positioning, I have shown the two lamps being wired into their solder dots . . . . but they are actually located on the other, now sealed off side of the board.

FUTURE NEEDS AND REQUIRED CAPABILITIES . . .

Initially, I am thinking of one shortcut work around to try.
But, if this leads to having to pull the front panel / bezel . . . made of thin,ferrous tin plated sheet metal.
That task will require a soldering iron, being and staying WELL tinned and a heat / wattage capability of melting those healthy solder blobs that you see at RED FLAGGED Roman Numerals I thru V and ?.
With their solders removal being via solder sucker, solder wick with added rosin flux assist.

I now await your finding . . . . . as our next task is the ascertaining of current consumption on that, now single 3 volt powered good lamp, which is needed to be found out.
( As it relates to the ***** previously above.)

Standing By . . . . . .
EatingPopcorn.jpg


73's de Edd . . . . .

Pastor told me last night in Revival

" you'll walk tonight"
Now I was thinking of that being directed to our in firmed . . . .
But . . . . It was true ! . . . . after the service, I went outside . . . . . . my car was gone . . . it had been stolen.


.
 
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Delta Prime

Jul 29, 2020
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Along with the EXTREME tangential in the troubleshooting erroneous direction now developing
[A9TTACH=full]59687[/ATTACH
That was absolutely wonderful.
I enjoyed that immensely.
photo_1686890275166.png
 
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die.nard

Jun 28, 2023
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Sorry for not replying sooner! You guys are amazing, that's the first time in years that I find a forum so active and helpful! Thank you so much Delta Prime and 73's de Edd!;)

nitially, I am thinking of one shortcut work around to try.
But, if this leads to having to pull the front panel / bezel . . . made of thin,ferrous tin plated sheet metal.
That task will require a soldering iron, being and staying WELL tinned and a heat / wattage capability of melting those healthy solder blobs that you see at RED FLAGGED Roman Numerals I thru V and ?.
With their solders removal being via solder sucker, solder wick with added rosin flux assist.

That's the way I have chosen! Lamps are both dead:

uc


uc


uc


However, checking the voltage when the board is connected to the rest of the radio (C-A poles on 73's de Edd diagram) I read 9.7V where I would expect 6.2V.... hmmm... :oops:

uc


Further inspection is needed... Solder splatter,
Oxidation, corrosion.
Also these things... to be honest I just verified the cassette player before dismantling the unit, maybe the rest doesn't even work :eek:

Thank you so much for your time!
 

Delta Prime

Jul 29, 2020
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Thank you so much Delta Prime and 73's de Edd!
We are both filled with copious amounts of adrenaline.:p
We make a very good team.
733333333'ssssss is all right with Meeeeeee'ssssss......
EatingPopcorn.gif
 
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Delta Prime

Jul 29, 2020
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(C-A poles on 73's de Edd diagram) I read 9.7V where I would expect 6.2V.... hmmm...
Your a natural troubleshooter.
I believe he was being facetious.
There are various other discrepancies as well....as I stated before in the photos submitted.
You should check the integral, essential, economic, practical discrepancies of your unit.
Economic feasible to maintain this period correct car radio
 

kellys_eye

Jun 25, 2010
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I read 9.7V where I would expect 6.2V.... hmmm...
Assuming you're measuring across BOTH lamps (they are wired in series) you would measure B+ whatever that is - the schematic doesn't extend to revealing that figure but I suspect it might be the battery voltage i.e. 12V DC.

You'd only measure 6V across ONE of the bulbs and that, only if both were working.
 
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