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liquid in trs-80 model 100 battery compartment


pacman000
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Got this a couple of years ago. Had some fun with it for a few months, then the display stopped working. It would switch back and forth from very dim to very dark. I copied what I was working on to a note pad, then put the TRS 80 away.

 

Got it out again today, to try it again. There was some sort of liquid in or around the battery compartment. Anyone know what's wrong? Google and Duck Duck Go don't.

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Open it and see what's leaking?

 

Since the caps are kind of small, I doubt they could piss enough to leak into the battery compartment.

There is a small rechargeable internal battery pack (for memory) attached to the motherboard. That definitely could have leaked, and if so, the board may be trashed.

 

As far as the dimming goes. If cleaning the brightness pot doesn't fix it, then this is your problem...

http://technobly.com/2016/08/21/fixing-a-trs-80-model-100-lcd-issue/

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Finally got this open today, but I can't find anything that's leaking. :?

 

post-62192-0-51153500-1512422404_thumb.jpg

post-62192-0-75946400-1512422452_thumb.jpg

 

There may be two capacitors that are leaking/have leaked, but I can't see that it ran anywhere.

post-62192-0-20593600-1512422486_thumb.jpg

post-62192-0-06606400-1512422526_thumb.jpg

 

From what I can tell the battery looks good:

post-62192-0-92399200-1512422571_thumb.jpg

post-62192-0-68347000-1512422614_thumb.jpg

post-62192-0-88336700-1512422660_thumb.jpg

post-62192-0-14882000-1512422765_thumb.jpg

 

I know this isn't a trouble shooting forum. Forgive me, but this is a mystery. I've never tried to fix anything electronic before. Should I try to take the PCBs out to see if there's anything wrong under them?

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Those may be droplets on the battery compartment; I didn't notice them before. There were droplets on the keyboard/screen PCB.

 

There was something on one of the chips behind the screen. I wiped it off with a rag. (Hope that was the right thing to do.) I think it was old battery corrosion; when I got it someone had left batteries in it and they'd gone bad. Still worked tho, once I got new AA's in it.

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Nice camera work. I'm expert in PCB repair. I am not expert in Model 100 repair specifics. I will make some technician observations and commentary.

 

 

1- Check/clean any brightness/contrast adjustment knobs. And inspect/reflow solder joints on those knobs. Check/clean/reseat any connectors related to the display and its cable. And considering the age of this rig, consider testing and replacing any electrolytic capacitors. While there are a lot of them - you can begin with power supply - and that could be all you need. You'll just have to go by trial and error.

 

2- I spy 5 electrolytic capacitors that could be power related, two big ones and 3 small ones near a yellow transformer. T26. And it's my guess they are in the power supply & regulator circuit. And it is my guess again the big two ones should be checked first. They're big because they're filtering and buffering power. And you want to ensure clean power to displays, whatever technology they're based on.

 

3- M11, in the vicinity of Pins 11,12 there are three vias. Is there any corrosion there?

4- And what the splatter stuff on M10 and M5?

 

5- Pin 61 of M10 connects to a trace that also connects to M5 Pin 61, is that trace good? It looks like something got under there, corroded the copper while leaving the upper "resist layer" intact but mottled.

6- On M10, right below the 2 in the "24" marking there is a via, it is discolored and looks like something got in there, and directly below the via at ab out the 7 o'clock position there is a tiny crystal deposit.

 

7- On M29 and M30 I see corrosion on several pins. The TL064 ICs. This isn't too far from the round connectors and the blue transformer OT1. They're discolored. And where they are soldered to the board you can see some green crystalline material. These parts appear to be in the modem circuitry, and would only affect the display through changes in power requirements due to improper biasing (setup so to speak) or through direct shorts.

 

8- I see corrosion/deposits on R37 and R45, right in that area.

 

9- There's a drop of something right by the R26 printing.

 

10- There are signs of dried liquid on the two large 25-Pin connectors on the back, CN5 and CN6.

 

11- I wonder what the bottom side of the board looks like?

 

12- What is the condition of the metal plating on the battery compartment contacts?

 

13- Evaporating and outgassing could affect the LCD glass connectivity to the display board. Etchings on the glass itself can be eaten away. This is a guess, again, and something I might inspect if this were my project and I wasn't having any luck elsewhere.

 

14- That's what's visible at a quick look over. There are likely areas not visible that are affected. And we don't know what they are or where they are. Or if they are electrically involved with the display.

 

15- The display potentiometer is quite close to the battery compartment!

 

And here is some documentation to use. I have not read any of it other than glancing through the service manual. There's a flow-chart, schematics, parts list, timing diagrams, mini-datasheets, and some general theory of ops. This is decent documentation. Much like I've come to expect for computers of that era. Very similar to what Apple produced. And anyone that's read my comments on Apple publications knows how much I respect the work put into those manuals.

http://www.club100.org/library/libdoc.html

 

---

 

My personal recommendation is to follow points 1 and 2. Pay good attention to the Brightness potentiometer knob. Be sure corrosion or contamination inside and around it aren't affecting operation. Be sure it has nice smooth linear operation verified with a DMM or even scope if you're so inclined.

 

Then I'd clean those spots and traces and test the continuity of traces that are discolored (either lighter or darker).

 

Since there are signs of corrosion either by direct liquid contact or vapor condensation from battery outgassing and spent electrolyte evaporation/recondensation, I'd be inclined to neutralize and wash the whole board. Doing this is going to be a little involved because you may have to remove some components that can trap water and which won't dry out easily afterwards. This is something I'd do to ensure reliable functioning now and for years to come.

 

 

EDIT: ADD POINT #13, #14, #15

Edited by Keatah
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I will see if I can get on my other computer and mark up the photos with red boxes indicating the trouble areas. The old ball and chain is busy with those nonsense games again.

 

EDIT:

 

I'm on my Photoshop computer now. I'm highlighting the areas that show corrosion/contamination. Please keep in mind this is indicative of electrolyte deposits. And both "other" circuitry and display circuitry is affected.

Edited by Keatah
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Old battery acid acts strange and seems to get everywhere...it almost acts like condensation. I'm betting that's all it is and fortunately it doesn't look like it hurt anything.

 

DeoxIT cleaner is great stuff for cleaning the brightness pot and any connectors. Radio Shack used to sell it; unless you have a local electronics shop, you may need to order online.

There's a 50/50 chance cleaning the pot will cure your screen problem. If not, that link I posted will take care of it.

 

Be careful with the PCB that the screen is attached to. The zebra strips don't age well, and if disturbed, you can get lines of missing pixels. Actually, it's a very common problem on the 100. If it is an issue, you can gently tweak those 14 gold tabs for a tighter fit and that will often cure any dead areas.

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Finally got another good chance to work on this. Opened it up, sprayed cleaner on the areas Keatah and Turbo-Torch suggested, sprayed cleaner around the pot. Brushed bad looking areas with a small paint brush. Let it dry out. Closed it. Put batteries in it, and it worked! Thanks Keatha! Thanks Turbo-Torch! I'll let it run for awhile, to see if it starts acting funny, then screw it back together if nothing else goes wrong.

 

Again, Thank you for your help! It was greatly appreciated!

 

Thank You!

 

EDIT: Oh...it turns off automatically after 10 minutes. Ok. Had me worried there for a second. :)

Edited by pacman000
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:thumbsup:

 

Finally maybe clean up any overspray and work the pot brightness/contrast back and forth a few times. If it goes bad "all of a sudden" then it was bad to begin with. If it works smoothly now it will likely continue to work for a long time.

 

Meantime, while the cleaner stuff is drying out. Why not go read some of the manuals for it? These were cool little rigs back in the day, and journalists loved them and their real-world connectivity.

Edited by Keatah
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  • 2 years later...
On 12/4/2017 at 4:36 PM, Turbo-Torch said:

Be careful with the PCB that the screen is attached to. The zebra strips don't age well, and if disturbed, you can get lines of missing pixels. Actually, it's a very common problem on the 100. If it is an issue, you can gently tweak those 14 gold tabs for a tighter fit and that will often cure any dead areas.

OK, I was trying (and failing) to find information on possibly repairing this. (A single dead horizontal pixel line)

Was mostly finding people who just replaced the screens.

This gives me hope that I might be able to do this.

(I don't know what/where the "14 gold tabs" are (under the ribbon cable or ??), but I assume I will see them once I more completely disassemble the unit.)

 

Thanx!

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2 hours ago, desiv said:

OK, I was trying (and failing) to find information on possibly repairing this. (A single dead horizontal pixel line)

Was mostly finding people who just replaced the screens.

This gives me hope that I might be able to do this.

(I don't know what/where the "14 gold tabs" are (under the ribbon cable or ??), but I assume I will see them once I more completely disassemble the unit.)

 

Thanx!

 

In post 5, look at the second picture.  On the top circuit board there are little tabs that are twisted which holds the screen to the board.  Sandwiched between are rubbery zebra strips (that you won't see).  If just one has poor contact, you lose a line of pixels. 

I use a pair of needle nose pliers to try and tweak the tabs so the board presses tighter against the strips and lcd...most of the time it works.

I've had a few where it didn't help, and removing the board to try and clean the zebra strips made things 10X worse.

 

I've not found new zebra strips and even asked around at Tandy assembly each year and no one is making repros yet.

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