TI-58C Display Problem

[DANTONVB]

I just bought another TI-58C, in almost new aesthetic condition.

It had broken battery contacts, due to battery leakeage, but it was operating as expected. Then I cleaned the battery residues in the calculator PCB, using vinegar and after rinsed with water, and soldered new battery contatcs. The calculator continued to operate as a new calculator. Next step was to perform Solid State Library ML-01 auto test, and the result was OK.

But in the next turn-on the calculator began to present a display behavior problem, with the display of the digits as the picture attached. The image is just after activation and the leftmost digits are always present and change as I enter numbers to be calculated. The calculation appears to be OK.

Do you have an idea of the cause of this problem? Do you sugest a repair procedure?

Thanks, Danton

[teenix]

(11-20-2018 09:43 AM)DANTONVB Wrote:  It had broken battery contacts, due to battery leakeage, but it was operating as expected. Then I cleaned the battery residues in the calculator PCB, using vinegar and after rinsed with water, and soldered new battery contatcs.

Cant be sure, but it is possible that the battery leakage caused a "thinning" of the pcb tracks by corrosion. Cleaning that corrosion off might have thinned them even more and they might now have some resistance or a hair line crack which is affecting the display operation.

I would re-check the pcb to make sure everything looks ok, ie nice clean solder joints, not dull and pitted, pcb tracks intact and no moisture from the cleaning hiding under IC's etc.

Corrosion may have affected a components connection to the pcb and it can be loose. Gently wiggling components like resistors and capacitors might show up a problem.

The IC's on the board will be sensitive to static discharge from fingers etc, best to handle the pcb by its edges.

cheers

Tony

[KeithB]

(11-20-2018 09:43 AM)DANTONVB Wrote:  I just bought another TI-58C, in almost new aesthetic condition.

Then I cleaned the battery residues in the calculator PCB, using vinegar and after rinsed with water, and soldered new battery contatcs.

Thanks, Danton

Isn't the corrosion acidic? shouldn't you clean it with something like baking soda to neutralize it?

[DANTONVB]

(11-21-2018 06:52 PM)KeithB Wrote:  

(11-20-2018 09:43 AM)DANTONVB Wrote:  I just bought another TI-58C, in almost new aesthetic condition.

Then I cleaned the battery residues in the calculator PCB, using vinegar and after rinsed with water, and soldered new battery contatcs.

Thanks, Danton

Isn't the corrosion acidic? shouldn't you clean it with something like baking soda to neutralize it?

I just rinsed it with a lot of water after cleaning with vinegar. The first operation after cleaning it was operating ok. The next operation the problem began.

[burkhard]

(11-21-2018 06:52 PM)KeithB Wrote:  

(11-20-2018 09:43 AM)DANTONVB Wrote:  I just bought another TI-58C, in almost new aesthetic condition.

Then I cleaned the battery residues in the calculator PCB, using vinegar and after rinsed with water, and soldered new battery contatcs.

Thanks, Danton

Isn't the corrosion acidic? shouldn't you clean it with something like baking soda to neutralize it?

I believe that dry cell batteries (including old Ni-Cad) use an alkaline electrolyte, hence a weak acid (like white vinegar) is what you want to neutralize with. Baking soda would be the ticket for lead-acid batteries.

[DANTONVB]

Yesterday the display began to only show C on the left side, when turned on. The calculator does not respond to the keyboard.

Today I again cleaned my TI-58C. This time I used a baking soda solution.

Noting changed. The C continues on the display.

[teenix]

(11-23-2018 12:38 AM)DANTONVB Wrote:  Yesterday the display began to only show C on the left side, when turned on. The calculator does not respond to the keyboard.

Today I again cleaned my TI-58C. This time I used a baking soda solution.

Noting changed. The C continues on the display.

There still may be a corrosion problem on the PCB, or now that the pcb has been "disturbed" something on it may have failed or has gone open or short circuit, possibly due to the original corrosion.

It is hard to say without a close inspection.

cheers

Tony