HP 15C LCD Replacement

[DavidRicchetti]

    I have a vintage 15c that I still enjoy using. The LCD display is “bleeding” and has grown to the point that it obscures part of the readout. I’m attempting to replace the display and hoping to get some advise as well as to share my experience should someone have the same problem.

I’ve noodled around a bit and from what I gather there are a few different builds of the Voyager series calculators. I found a thread on this forum that recommends finding a replacement display from a donor calculator of the same build type. My 15c has a serial number starting 2328A… so I found a 12c with a serial number starting 2224A… with the same style battery connectors. How hard can it be?

Here’s a link to the thread… https://www.hpmuseum.org/forum/thread-29...er+display

I also found an article from 1982 showing the insides of an 11c of the same build type at valc.net here… https://www.hpmuseum.org/forum/thread-29...er+display

It looked like I would be able to swap-out the part called the “display module” and be done. No such luck. The so-called display module includes the processor so swapping a 12c display module will turn my 15c into a 12c. So I guess I need to remove the LCD display from the display module and swap out only that part. I may be in over my head!

I haven’t been able to find a detailed description of how that’s done so I’m hoping someone can point me in the right direction.

Many thanks!



[Marcovecchio]

I don't have pictures, but the first step would be to remove the black film that wraps the module. I'm pretty sure it's not important to reinstall it, so don't worry about keeping this film intact.

I'm not sure about this paragraph, since I never opened a module like this, but here goes: the metal frame surrounding the LCD will have tabs folded over the pcb, to keep pressure on the two zebra strips you will find below the LCD, at the edges. Unfold the tabs carefully, pull the metal frame, and you will have the LCD loose, and ready to be replaced.

If you can, transplant the LCD WITH the attached zebra strips, avoid unattaching then from the LCD glass. Electrical contact there is delicate, any dirt will make it fail, and cleaning is very tedious. When replacing, you have to realign PCB tracks to almost invisible electrodes in the glass. I do that with magnifying glasses. Some models are hard to align, like the hp48 series, but Voyagers are easier, and the most recent models have pins that fit in PCB holes to make the alignment. I don't know if these older modules also have alignment pins.

The first Voyager LCD model has been fitted to machines built until 1987 (serial 27XXXXXXX). Source: http://www.brouhaha.com/~eric/hpcalc/voy...iants.html

Good luck!

Eduardo

PS: what started the bleed? Was it spontaneous? Or the calculator suffered a drop?

[DavidRicchetti]

Thanks for your thoughtful reply Eduardo.

Well, it’s encouraging to hear that I may not have fouled it up beyond all repair. I did remove the black adhesive film wrapping the module. I’m glad that you think it not important, because it came off in a couple pieces; still very sticky after thirty-seven years.

I should have time this weekend to give it another attempt. I think I’ll try my hand at the 12c donor to see how it goes before risking further damage to the 15c.

In answer to your PS… I have no idea what caused the bleed. It’s never been dropped or damaged in any way, in fact, it’s otherwise in excellent condition.

I’ll report back. Thanks again!

PS: looking back at my first post I see that I pasted the wrong link to the vcalc.net page… here’s the correct link… http://www.vcalc.net/hp-11.htm

[Marcovecchio]

Good luck in the surgery!

And exploring the 12c donor before the 15c, is a good idea. Regarding the film you removed, it was used as an electromagnetic shielding, which proven unnecessary: newer models (from 1984, 85 or 86, I'm not sure) have a much simpler construction and no shielding film at all.

And be patient when replacing the LCD. As I said, if there are no alignment pins, you'll have to align by hand, and this hardly works on the first attempts. But it's quite doable, you only need a bit of practice, and perhaps some isopropyl alcohol to clean the zebra strips and LCD contacts.

Eduardo

[DavidRicchetti]

Success!

I seriously doubted I could pull it off but the calculator gods must have taken pity on me. Thank you Eduardo! Your instructions and advise spared the life of my beloved hp 15c. It’s now sporting a crisp and clear LCD display and passed the internal self test as well as the keyboard test.

I’ll follow-up with a post detailing the process and sharing a few tips from my experience along with some photos.

David

[Marcovecchio]

This is great news, congratulations!

I'm looking forward to see the pictures and to know more about the surgery!

Eduardo

[DavidRicchetti]

Alrighty then… In case someone is searching this forum for instructions to replace the LCD display on an early build of a voyager series calculator… here goes…

Step 1 — Find yourself a donor calculator of the same build type. I understand that if both calculators have the flat clip-on battery connectors at two ends (not the coil spring connector on one end) then you should have interchangeable LCD displays; and the same display was used for all the calculators in the voyager line (10c, 11c, 12c, 15c, and 16c).

   

[DavidRicchetti]

Step 2 — Open the calculator. I recommend starting with the donor calc to get a feel for the process before you risk the calc you’re trying to save. First remove the battery cover and batteries and gently remove the rubber pads covering the screws at all four corners. Try to get under both the piece of rubber and the two sided tape so they come off as one. I used a product called Goo-Gone to removed the residual glue from the calculator without damage. Then remove all four screws and lift the back of the calculator off with the keyboard facing down. Note that there are two small coil springs that you may want to remove so they don’t get lost; the larger one goes in the hole near the display. Note also that one or more of the small square foam washers, that fit on the four posts holding the display module, may be stuck to the back cover of the calculator; don’t loose them.

   
   

[DavidRicchetti]

Step 3 — Unwrap the anti-static film. Note that there is a piece of double sided foam tape stuck to the printed circuit board behind the keyboard. First gently lift the right side releasing it from the foam tape then the left side. I held the two sides open by taping them to my work surface. Note also that there are two clear plastic tabs on each side between the front case and wrapper that you can just leave in place or remove and replace later.

   

[DavidRicchetti]

Step 4 — Remove the display module. Remove the two battery terminals that are connected to the red and black wires by sliding them up to unclip them from the plastic case. The display module can be lifted up along the four plastic posts that hold it in place. Note that there are two additional plastic post penetrating the flexible circuit at the right top corner; and that between those posts is a zebra connector. Take care not to lose that zebra connector should it come loose from the flexible circuit. Also note that there are eight small foam washers to keep track of; four on each side of the display module on the plastic posts.

[DavidRicchetti]

Step 5 — Remove the LCD display from the display module. First you have to remove the mylar film tape covering the back of the display module. As Eduardo explained in the thread above, this film is likely not necessary and can be discarded. Which is a good thing because it’s extremely sticky and will most likely come off in small pieces. Note that the film tape is not shown in my photos as it had already been removed. Then you need to remove the pronged metal frame that holds the LCD display in place; it’s made of spring steel. Good luck with this! I found it was easier to release the four prongs along the edge with shallower indents first while holding the LCD in place. Once the metal frame is off slowly and gently lift the LCD from the flexible circuit being careful to try to keep the zebra connector attached to the LCD (see Eduardo’s description above). Also, be careful to pay attention to the orientation of the LCD so you don’t put it back together upside down.

[DavidRicchetti]

Step 6 — Repeat the process with the other calculator, swap out the LCD displays, and reverse the process to put them back together. I suggest you follow Eduardo’s advice above about taking care to properly align the zebra connectors on the flexible circuit and cleaning them first with alcohol. Mine worked on the first try, thanks to Eduardo’s advise, and a good measure of dumb luck!

   
   

[EdS2]

Great notes - thanks, and congratulations!

[Marcovecchio]

Thanks for the detailed procedure and pictures, David! Great work, and I'm glad to know it worked on the first try!

Eduardo

[BillBee]

Thank you for the write up. It is much appreciated and I hope to use this as motivation to replace the LCD on my trusty old office 11c it has a similar serial # with separate LCD module. It took a bump and has the screen bleed on the far right side so its still useable but it nags at me.

-Bill

[DavidRicchetti]

Here's wishing your 11c a long life Bill. BTW, I found a 12c donor on eBay for about $20.

-- Dave

[BillBee]

Thanks Dave!!

I have also been working on the wife regarding a Swiss Micros.

Regards!
Bill

[GreyUser]

For the sake of completeness, please allow me to add the following:

One important tip when doing this work: wear a pair of latex gloves. It prevents skin oil from transferring to contacts and zebra connectors. No cleaning, other than maybe canned air to keep the loose dirt off things is required when working this way.

As the OP experienced, the replacement is easier if the replacement lcd is from the same vintage/design as the target machine. That is if your target machine has two identical tinned battery connectors, look for the same in a replacement 12C. If the target has a coil spring on the left and a gold pc protrusion connection on the right, look for the same in a replacement.

The procedure outlined above is for the original design Voyagers that are wrapped in what HP called the black diaper. It was anti-static protection for the sensitive cmos electronics. It was later determined that it wasn’t necessary with HBM (human body model) testing and was eliminated when the product was redesigned to reduce the assembly costs. What is important for anti-static protection are the two small coil springs that connect the front aluminum keyboard surround with the aluminum plate of the back cover.

The difference between the two lcd’s is the height of the zebra connectors, the design of the metal frame that secures the lcd to the supporting structure (plastic or pc board) and most importantly, if the display is mounted to a plastic carrier for easier installation during manufacturing.

While the actual lcd’s are identical, the chances for success are greatly increased when parts match, especially when this is your first attempt. Why is this? The answer quickly becomes obvious trying to remove a lcd from a plastic carrier to be used on the earlier design unit. The double sided tape is quite tenacious and it’s unnerving prying on a glass lcd...

When the replacement part matches the defective part, do not, and I repeat, do not remove the zebra connector strips and further, do not remove the lcd from the metal frame. Remove the replacement by using fine point tweezers or a very small diameter straight blade screwdriver by lifting the bent tabs on one side just far enough so they stop mid point on the plastic frame or pc board.

Repeat with the opposite side.

Now, with all the tabs half way removed, completely pop off one side. Then repeat with the opposite side. If the zebras are stuck, slowly peel the display off by holding the metal frame and lifting from either end. The early model with the flex pc tend to stick often but they are easy to peel. The later design can be problematic to remove if stuck due to the plastic locating pin on the black plastic backing plate that the lcd is double sided taped to.

Once the donor lcd is off, it can immediately be transferred to the recipient. The zebras do not need to be cleaned if you don’t touch them. You can clean the gold contacts if there is a chance you touched them without gloves on.

Just reverse the removal process. Place the display in place. Don’t flip it, the glass to glass seal goes on the right side. Start one side one half way, repeat. Then seat one side and then the other.

Reassemble and test.