Here we go.... (48G fixing and MEMORY UPGRADE)

[lemontea]

Ok folks, there's a lot to update.

I will do it gradually one post at a time for each "stage" I have gone through...

It has not been easy!

Please take a look at the photos (it's also annoying I have to resize them but the thing I would prefer most is being able to put them inline, so it is easier for you guys to refer to as I go along describing the process).

Anyway I opened up the top half where the keypad and LCD reside (basically, removed the PCB).

It's not easy to twist those metal tabs, and it is also not easy to prevent the PCB dust. In fact in retrospect now I think one should wear a dust mask doing this (because you probably will be putting the PCB on and taking it off again several times to test things, and every time the metal will scrap and produce some fiberglass dust). This dust mask is in addition to standard eye protection.

So as you can see, there's corrosion at the keypad contacts.

I cleaned with isopropyl alcohol wipes, and some q-tips.

The oxidation or whatever on the copper pads, I tried to scrap a bit to make it more conductive. You can see the attempt in the photos.

[lemontea]

Didn't realize I could only upload 5 photos...

Here are 2 more.

Anyway you can see the conductive paint on the keypad connector also faded away.

[lemontea]

Ok, so after cleaning the contacts, I reassemble the top half.

It is NOT easy to reassemble, as you are trying to NOT twist the metal tabs too much (just enough to make the PCB stay), since you are still testing, and then you don't want to create the PCB dust (either so you don't breathe it, and/or not have it fall onto the LCD connectors --- more about THAT one later).

Now, power test!

I tried to reassemble the calculator with the bottom half.

WHAT A HASSLE!!!

It is even harder to close up than to open it, if you can believe that!

The heat stakes are probably the problem, as the latches seem to close fine. Anyway after some time I decided to leave the closing up for later. I am still testing anyway.

So, need to power the thing.

Out comes my alligator clips and... should I use a power supply or just batteries?

Let's go with batteries. Don't have AAA battery holder but AA should do. Found a 3 AA holder that I salvaged a few years ago from some junk toy (knew it would come in handy, even though my wife said otherwise, haha!).

Well, did the calculator power on?

Big fat nope!

Maybe it needs more cowbell...

Ok, let's bring out the wall adaptor, set to 4.5 volts...

Still doesn't work!

[lemontea]

So........

Maybe the PCB is kaput or whatever.

Well, how about using another PCB?

So I got a broken 48G from YOU KNOW WHERE for around $10.

LCD is busted, and they keypad overlay is terrible.

But maybe the PCB works fine?!

So....

[lemontea]

But it's heartbreaking to see a 48G overlay in such disrepair...

So I just had to try to fix that and also maybe I will fix the LCD later. It should be a simple job right? (Ha!!!)

Anyway, taking off the metal overlay was NOT EASY EITHER.

I tried a few ways carefully, then finally I figured out what I would do is mount a heat gun on a vice, and then WEARING GLOVES I would heat parts of the overlay and carefully pull on it.

This worked, but the top part was stubborn and I overheated the plastic a bit much and warped it.

Well, had to learn somehow.

THEN I tried to flatten the overlay with some various methods, until eventually I decided to take a roller from the kitchen to smooth out this 20 year old sheet of dirty metal. (Don't tell my wife).

[pier4r]

A tip. For images you may use imgur.com, it is a bit more user friendly than forum attachments. Just be careful not to link super sized pictures.

[lemontea]

So then I figured, maybe I should just remove that nasty LCD anyway.

(Thought I was supposed to work on the PCB... anyway...)

Since the LCD was already busted, I didn't have to be super super careful.

Just careful enough not to break it and cut my fingers.

Then how the heck would I be able to type all this and report back to you guys huh?! Right?!

[lemontea]

(05-31-2017 08:05 PM)pier4r Wrote:  A tip. For images you may use imgur.com, it is a bit more user friendly than forum attachments. Just be careful not to link super sized pictures.

Thanks but anyways I am already in the midst of it, might as well just keep uploading this time...

[lemontea]

Yucky LCD removed.

(So, just to be sure, remember that this is from the second 48G unit. So there's no problem on the keypad connector).

[lemontea]

(Email just came in, got work to do. Back later with more posts).

[lemontea]

Alright, where were we?

So yes, I removed the damaged LCD.

Now, you can't have a 48G faceplate without an LCD. It's got to be sacrilegious or something.

So needed to find a replacement LCD.

What better than to check for any other device with the same LCD?

Why, a 39G of course, which can be had for CHEAP.

Had to wait a few days again for it to be shipped...

Opening the 39G was EASY compared to the 48G.

Surprisingly, it was also heat staked at the bottom. Since I didn't much care about the 39G (darn thing's algebraic anyway) I carefully pried open the top bit, and then for the finale, I simply applied many newtons of force and ripped it open.

Actually everything looked pretty good, pretty intact.

The VERY INTERESTING part is that it looks SO MUCH like the 48 series layout!

Note the HUGE IMPROVEMENT on the +ve battery terminal, with the insulation pad underneath the chassis -ve ground plane.

[lemontea]

OK, so here's where we are at.

The first 48G didn't work even after cleaning the contacts. Might be the PCB itself, or the PCB contacts, or the keypad contacts.

The second 48G has a busted LCD. It is from this second 48G that I want to get a PCB, to try on the first 48G (which still has damaged keypad connectors, and also unknown status of the keypad itself).

But maybe the second 48G only has a damaged LCD problem. If the LCD is replaced, maybe it would work? It would narrow down the detective work, because if I just put the 2nd PCB into the 1st 48G, there are multiple unknowns (PCB, Keypad connector, Keypad...)

So, perhaps it is best to replace the LCD on the 2nd unit, and then see if it works first.

So, let's take out the LCD from the 39G.

The plastic cover is MUCH harder than the softish plastic of the 48G. The LCD even has another clear plastic cover protector.

Since the 39G is to be salvaged (it actually doesn't even turn on either, despite the auction listing saying it does, with photos to show, but anyway that's not what we are concerned about) I just bent up the retaining structure around the LCD to make it easier to take out.

The LCD was kept intact, with its foam connectors all intact, and completely removed.

[lemontea]

Now, here is yet another hurdle, which I shall attempt to describe in detail.

The NEW LCD (yay! Black LCD!) was put carefully back into the frame for the 2nd 48G, the one with busted LCD and the dented metal overlay (which I smoothed out).

I had smoothed out and replace the overlay, using some contact cement. Still, hardly "pristine" looking, but I just wanted it functional. It would be darn near impossible to bring it back to a factory condition without some good equipment. I almost figured I would just print out a new overlay with my inkjet printer, but then I would have to cut out all the little holes, and I would not even know if it would be worth all that effort if the thing didn't work.

So, I glued back the overlay, and then carefully put in the new LCD.

Here, it is super tricky.

If you have read Han's repair web page, you will know that he cautions about replacing the LCD, to ensure the foam connectors are all lined up properly, and to avoid any dust on the connectors.

I don't know how he does it, but it seems close to impossible to do.

The reason is, I don't know when the foam connectors are lined up. There is wiggle room on the metal chassis, so you can veer left or right a bit, and if the offset is too much (look at the spacing of the PCB's LCD connectors) it seems you will be totally misaligned.

So, I just tried it a FEW TIMES (so much effort!), moving the LCD ever so slightly left or right if it didn't work. (Note that we are still using the 2nd 48G's original PCB).

Meanwhile, when you push the metal tabs through the PCB, it is IMPOSSIBLE not to generate PCB dust.

(I thought about spreading some coating on the PCB holes to prevent the dust, but the holes are too small and there is no tolerance around it because the PCB copper traces are too tight and close.)

This PCB dust EASILY gets onto the LCD foam connectors, even if you hold up the PCB over your head as Han recommends (here again, I think we should be wearing dust masks and eye protection, especially if you are going to hold the assembly overhead).

Then you need to carefully twist the metal tabs again to secure everything.

AND STILL IT DOES NOT WORK.

I tried several times. Quite tiring work!

LCD comes on but incorrectly. You can see various attempts in my photos here.

(OOPS it says I have reached my attachment quota of 6 MB... hopefully someone can help me fix this, so that I can continue posting. I will stop now until this is fixed. Back later today or tomorrow).

[mfleming]

(05-31-2017 07:48 PM)lemontea Wrote:  Now, power test!

<snip>
Well, did the calculator power on?

Big fat nope!

One mistake that's easy to make is to fail to fully seat the circuit board before retwisting the tabs to their original position. You should press down on the board in the area near the tab as you retwist it. The firm seating is needed to provide good electrical connection between the circuit board and the keyboard & display contacts beneath.

Another thing to watch for is that the twist tabs serve to connect the circuit board to ground. When you twist them back to their original position, make sure the pad ends are touching the copper pads beneath them. I always do a continuity test between tab and pad after reassembly. Try that now to see if you might have a bad connection.

Thanks for reminding me I should do a black LCD transplant someday!
~Mark

[Han]

Your most recent photo suggests that the connector pads for the LCD screen on the PCB are not lining up with the corresponding signal lines on the screen itself. This is why you are getting garbled lines and rows and partial annunciators being lit.

If you look at the "rubber connector" that connects the PCB to the screen, you can probably make out where the rubber connector lines up with the twist tabs because they (the twist tabs) leave a slight indentation into the rubber connector. I find that this helps with the alignment of everything.

Another tip is to use a small piece of stiff clear plastic (or something similar) to place over the screen (overlay side) and some non-conductive material on the PCB side. Then use a small clamp or two to hold the PCB into place. The clamp(s) will make contact with the protective clear plastic on the overlay side (spreads the pressure onto the overlay so that the screen is not damaged), and your non-conductive material on the PCB side (I have metal clamps). Now you can test the alignment without having to use the twist tabs. Adjust until everything is perfectly aligned. Then twist the 6 tabs into place. This method allows you to adjust as much as you like without wearing out the twist tabs.

EDIT: Also, if you know for sure that one of those HP48's is not salvageable, then cut out the bottom portion of the case (the battery part) so that you can use a makeshift battery holder and not have to rely on alligator clips.

[lemontea]

Ok thanks guys, will proceed with your suggestions next round.

[lemontea]

Going to try uploading the 2 further photos of the first LCD test.

Nope, it still says "Sorry but you cannot attach this file because you have reached your attachment quota of 6 MB"

So is this forever on this site now?

[Eric Rechlin]

(06-02-2017 03:29 AM)lemontea Wrote:  So is this forever on this site now?

Yes. Don't use this site's attachment feature; it's useless. Upload to something like imgur.com instead and link to the images.

[lemontea]

OK signed up with that IMGUR site. Never used it before.

Here's the first batch of LCD tests.

This was before receiving tips from Mark and Han.

http://imgur.com/gallery/Dmz5w

[lemontea]

Now, here are the results after following Mark's and Han's tips, although actually, not quite.

I did check the connectivity with the tabs that Mark pointed out. Seems like actually on the underside of the PCB there are already contacts to the ground plane. But I did also check that the twist tabs contacted the copper pads.

However, at this point, the tabs and pads have been worn away quite a bit from all the trial and error. I am not sure how long more they will last.

I also didn't manage to use Han's tip about clamping the LCD. Couldn't find anything appropriate to make the "LCD sandwich" and don't have clamps anyway (not for that small size).

So, after QUITE SOME TIME (maybe 2 hours?) of jiggling around, I pretty much just wanted to call it quits, because it's really not easy. I also had to use a camera lens air blower to get the fiberglass dust away from the LCD connector (while having the PCB obstructing my view and the air blower...).

All in all, pretty darn frustrating.

So then finally, I decided, heck, just put the PCB back in and call it a night.

THAT'S when this happened:

http://imgur.com/a/3Jnoe