[jwhat]

Hi SGI'ers,

has anyone had experience either fixing or replacing the LCD display unit for the L2 controller ?

I am talking about these:



This one looks ok in photo, but in real life it is very dim.

It is another part of the O350 rebuild I am currently doing.

Thanks in advance for any help/suggestions.

Cheers from Oz,


jwhat/John.

[weblacky]

For monochrome LCDs isn't "dimness" a function of proper voltage (contrast setting), I mean can a monochrome LCD "wear out", I didn't think that was possible. Isn't the contrast a function of voltage applied to the certain property of the LCD? Perhaps you could try to look at the caps on the LCD PCB and try replacing a few to see if that "darkens" the display back to normal?

Perhaps you have pics?

[jwhat]

Hi Weblacky,

I know that the old/original Mac PowerBooks becomes unusable due to inability to get proper contrast with monochrome LCD.

The underlying issue is voltage , due to leaky capacitors, so options are replace the leaky capacitors (there are a lot of them in the display) or replace the display and hence also get new capacitors with it ...

I have a old Mac with this exact isssue, sitting in my "too hard basket" as I am an inept solderer (clumsy fingers, shakey hands and bad eyesight are my excuses).

So I believe you are right about underlying cause, question is what is best way to fix it.

The display has "contrast" slider on it an I used this to get best result before taking picture.

As always thanks for responding.

Cheers from Oz,


jwhat/John.

[Raion]

I have an origin 2000 one fwiw, I don't know if that helps.

[weblacky]

Jwhat, would you mind giving us some pics of the L2 LCD innards?

In terms of soldering, I'm pretty good and have some great equipment, if you want to give it a try with new SMD caps, I'd be willing to try soldering them in for you for free. I guess my feeling is.

A. They don't make "new" L2 controller screens anymore.
B. There aren't that many L2 screens left in the wild, so I'd hate to see this thrown out when it clearly "works".

I don't have an L2 setup or anything myself, but I'd take a stab in the dark with you to further the cause. If you can get a good pics of ALL the caps, we can do some research and perhaps come up with a plan to replace them all and see if that magically brings back all your "variableness" for contrast settings?

[jwhat]

Hi Weblacky,

very generous offer.

I did open up the unit up a couple of weeks ago, but did not take any photos , as unit has 3 layers of closure:

• the plastics (easy)
  
• the steel casing internally (harder) and
  
• the gizzards in this (even harder)
  

I did not get to the gizzards layer ..

I will see if I can re-open it up next week.

Cheers,

jwhat/John

[weblacky]

Hi Weblacky,

very generous offer.

I did open up the unit up a couple of weeks ago, but did not take any photos , as unit has 3 layers of closure:

• the plastics (easy)
  
• the steel casing internally (harder) and
  
• the gizzards in this (even harder)
  

I did not get to the gizzards layer ..

I will see if I can re-open it up next week.

Cheers,

jwhat/John

 
Wow, as esoteric as these things are, they aren't cheap either are they?  I cannot find any good pics online either (even under the plastic).  As you said, it appears to be a big metal box under that playtime plastic case, but no other information.  No one has ever posted pics of the insides, online.

[jwhat]

Hi Weblacky,

agree with your sentiment that we need to keep these things going.

To help with that here are pictures of internals.

The back of display (the power/display cable is an MD50 / MD50 SCSI cable (thanks to "sgi-enthusiast" for providing this info), but to connect it up in rack requires a 7 feet cable). I have been testing with a little short one:



With the back off, this is steel enclosure:



And the two slides of steel enclosure circuitry.

For display:



For controller? :



To your point about not being cheap, the units weigh over 1 KG and are much more robust than pictures would make you believe.
Typical SGI engineering of the era.

Cheers,


jwhat/John

[robespierre]

It looks like only tantalum capacitors were used, so they are unlikely to be the culprit.
The backlight is a cold-cathode fluorescent tube and those do have a limited lifespan along with decreased emission. That would be cheap to replace. The inverter (module marked TDK) would also be a suspect as those commonly fail.
The 5.7", 320x240 LCD module itself is made by Samsung and is available new from eBay sellers in China for ~$100. It does not include the touch digitizer, of which you can see the cable emerging behind the LCD.

[weblacky]

I’m actually still dubious! OP is talking about darkness of the screen not brightness. CCFL only makes backlighting, the darkness is a function of the LCD crystal display blocking that light.

So, the boot screen for an L2 (online) claims it uses a SED137x driver, this uses a pulse-style transmission to convey contrast. So it’s either the display and PCB itself or the L2 circuitry it’s hooked to that scsi cable that’s responsible.

Say, do you have another L2 to check against, does another L2 have the same dimness or contrast range issue with this display? That would at least prove it’s the display module’s fault and not the L2 device it’s hooked to? It’s a start.


Also on the bottom of the controller board, there’s a cutout with like a slider control? Is that the contrast adjustment? If so perhaps find the in and out of that and measure it with a multimeter will tell use something. Assuming the display stickers I see give use LCD info. Maybe it’s already giving max contrast voltage or maybe that slider is dirty/faulty and not giving full voltage at 100%?

---

——————-
OK, update. There is apparently is a large retro digital watch community that tackles this same problem. They are saying that when it comes to monochrome LCD segmented style displays that the faded contrast is actually aging of the polarizing layer on top of the LCD.

They claim that you have two options if you know it’s not a power source issue. You can try to put linear polarizing film on top of the current film which will bring back a lot of the contrast but will interfere with the backlit intensity. Or you can attempt to strip off the original polarizing film on the front surface by removing the LCD from its entire frame and gently attempting to remove the existing polarized film and clean the adhesive and apply a brand new polarizing film.

You could easily see the affect of the first suggestion by buying various film sheets online and just place them over the current display. If it’s something you can live with then you’d need to separate the touch surface and apply the additional film.

There’s also the suggestion on this thread that it might be easier to find an exact/compatible LCD screen to swap into place with a fresh polarizer. That would require still likely trading the touch element and confirming the same screen connectors.