Tandata TD1404 Screen Corruption

[marrold]

Hi all,

I've got a Tandata TD1404 viewdata terminal and its suffering from the classic Tandata screen corruption on the Directory page.

I've had a play with it today and made a few observations:

* The Top "Tandata" and "Directory" text is always displayed without corruption.
* Saving new directory entries works and if corrupted characters on screen are overwritten with a telephone number or ID, they display the correct digits.
* Saved directory entries can be dialled as you would expect
* Perhaps more interestingly, pressing Func + Zero to Erase the memory beeps to acknowledge it, but doesn't actually erase the memory, either the newly entered entries or the corrupt sections.
* With a quick power cycle with the internal battery removed the directory entries are still there and corrupt sections are identical. But with a longer period powered off, the directory entries are gone, and the corrupt sections are different.

Otherwise, the unit works normally. Does anyone have any thoughts?

Screen on initial power up:



Screen after directory entries have been added:



Cheers

[marrold]

I made another observation, this model allows you to store and retrieve pages, however in my case I'm unable to store them as it believes all the slots are full. If I try to retrieve the stored pages they show the same corruption as the Directory. Like the directory, if I attempt to erase them the same corruption exists as if the erase is ignored.

Due to their size they must be being stored on the TC5517APL SRAM chips. Does anyone know anything about these, if they commonly fail, and why they not be erasing the data when instructed to?

Thanks

[1024MAK]

The TC5517APL are just normal 2k byte SRAM chips.

The fault you are experiencing is either one or more of these SRAM chips being faulty, a problem with the address, control or data bus lines to them (but maybe not affecting all of them if there are more than one), or a problem with the address decoding for them.

I can’t really go in to any detail without knowing more about the system, or better yet, having a schematic circuit diagram to study.

How many TC5517APL SRAM chips are there? Are any chips on the board in sockets? Is there any evidence that any components have been changed or worked on (such as flux left behind, or solder joints that were done manually rather than in a solder wave bath)?

Mark

[marrold]

Hi Mark,

There's 2x SRAM chips and they are socketed with no signs of re-work anywhere.

Unfortunately I've not seen or heard of a schematic. I've attached some more photos below which might be of use.









Thanks again

[marrold]

Hi Mark,

There's 2x SRAM chips and they are socketed with no signs of re-work anywhere.

Unfortunately I've not seen or heard of a schematic. I've attached some more photos below which might be of use.









Thanks again

[1024MAK]

You could try carefully removing the two SRAM chips and swapping them around, to see if this changes the symptoms.

If you’ve not removed a chip before, please ask for advice or search the forum for advice.

Mark

[marrold]

Good shout. I'm demoing it an event tomorrow so I won't tempt fate, but I'll try it when I'm back.

Cheers

[marrold]

Pernod requested images of the keyboard in another thread and I've sent them via the *. discord, but for posterity here they are:

[Pernod]

Here's the ROM dump, thanks to marrold who I met at CfCH yesterday, and to ChrisO for having an Acorn System setup able to dump the ROM.

[marrold]

Yes, great to meet you and many thanks to ChrisO for dumping the ROM