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Sometimes the LED display of Woodstock calculators don't show one or two digits, or one segment of all digits is missing complete. In most cases this can be easily repaired, because its only a loose contact of the common cathode of this digit or of the missing segment line. But if only a single segment of one digit doesn't show up, it cannot be repaired, because it is a contact problem of the very tiny microscopic bonded wires within the bubble display.

I made also acquaintance with completely corroded displays where any hope must be given up.

For these unrepairable displays I made a small layout last week, which replaces the complete display.

new display old display

I choose the QDSP6064 bubble display, which is available at SparkFun. It is also used by Chris Chungs wonderful NP-25 board.



The printed circuit board is compatible with the old display and can be replaced just by sticking it at its place.



The digits are slightly smaller than the original. Some of my HP-25s are brighter, others have the same brightness. And that's how it looks like.



Unfortunately the prototype boards I received today are not usable, because I made a mistake and placed the display off center by 2 mm, which doesn't look very good. I made a solder version which could be placed correctly for making the image above. If anybody has interest in this new replacement, and there is some demand, I will try to make a new batch, which I hope will fit perfectly then.

Of course, this was more easy than developing the new ACT

Bernhard

A very nice, useful idea! I wonder how long those bubble displays will continue to be available from Sparkfun. It's pretty clearly just one batch of NOS parts that they found, otherwise we'd see them all over ebay (there's just one seller now).

(06-22-2015 04:11 PM)Katie Wasserman Wrote: [ -> ].... I wonder how long those bubble displays will continue to be available from Sparkfun. It's pretty clearly just one batch of NOS parts that they found, otherwise we'd see them all over ebay (there's just one seller now).

It would be useful to buy a bunch of them before they will suddenly disappear. But how many?

Bernhard

When I wrote:

Quote:Unfortunately the prototype boards I received today are not usable, because I made a mistake and placed the display off center by 2 mm

I didn't recognize, that I can correct the position perfectly just by doing a SMT (Surface Mount Technology) assembly instead of the intended through hole assembly. Even this prohibits possible contact of the through hole pins on the bottom side.



Now the position of the digits are perfectly aligned in the center of the calculator display.

So I'm happy not to have to throw away my first 20 boards.

Bernhard

Wonderful news indeed, and good your PCBs are usable.

Of course, we have a tough crowd here, someone is going to ask if they make other colors besides red . . . .

(06-23-2015 01:00 PM)TASP Wrote: [ -> ]Wonderful news indeed, and good your PCBs are usable.

Of course, we have a tough crowd here, someone is going to ask if they make other colors besides red . . . .

I had already the same idea. I bought these russian green LED digits. As an optimist I still think I can arrange them somehow on the board. But I did not yet test whether they fit electrically and if they are bright enough. And they will be invisible through the red screen of the HP-25. It will be a not so easy task to replace it by a green glass.



Bernhard

Hi Bernhard
Thanks for the tip, I just bought some for spares.
They have over 4000 in stock, but who knows how long they will be available?
Regards
Ray

Bernhard, compliments for your idea!!!

Hi Bernhard,

Some Commodore calculators have the same displays as your picture of "old display". They are not sealed so the electrolyte of leaking batteries corrodes the bonding wires, and as you say there is no hope .

I have some 4-digit displays that I purchased for this reason but have not made any boards myself yet. I like pooling of resources, so I'd like to purchase a few bare boards from you.

-Bart.

(06-25-2015 09:33 AM)BartDB Wrote: [ -> ]Some Commodore calculators have the same displays as your picture of "old display". They are not sealed so the electrolyte of leaking batteries corrodes the bonding wires, and as you say there is no hope .

I have a Commodore SR-4190R with this issue and I'm wondering what it would take to replace the bad display with a new one using the Sparcfun LED modules:

(06-25-2015 11:08 AM)Didier Lachieze Wrote: [ -> ]

(06-25-2015 09:33 AM)BartDB Wrote: [ -> ]Some Commodore calculators have the same displays as your picture of "old display". They are not sealed so the electrolyte of leaking batteries corrodes the bonding wires, and as you say there is no hope .

I have a Commodore SR-4190R with this issue and I'm wondering what it would take to replace the bad display with a new one using the Sparcfun LED modules:

There must be met some requirements for replacing a display.

It must be a common cathode LED display, because the QDSP6064 has connected the cathodes of all segment diodes of each digit to one pin. It must be a multiple of four digits, because the QDSP6064 is a 4-digit module. Your SR-4190R display has 14 digits, which does not meet this requirement. Perhaps you can use 16 digits and don't use one on either side if there is enough space. In any case you must produce a wiring layout identical to your display pins. And the new height of the display must find space in the calculator. Sometimes there is no single mm left. In the HP-25 it fits perfectly, but the new digits are closer to the screen than the original. The voltages should be no problem, because all red LED modules uses the same forward currents at that time.

The HP-2x etc. LED displays are not sealed either. I have a totally corroded HP-19C module looking like yours. But I think I can replace that. Unfortunately all the other components are corroded the same and I still haven't started any repair.

Bernhard

I ordered some display modules in germany for this project. They have the same price than in US but in Euro.

I don't want to sell the bare boards. First I made a mistake as described above and the assembly is somewhat special. Second I will at least get some benefit for going on with these works.

Therefore I offer the assembled boards for 30 Euro + shipping. The components are 10 Euro, the board is another 10, and the rest is intended to keep me happy You could spare 10 Euro with the bare boards, but ...

If you want to order please PM or mail, I can deliver from tomorrow.

Bernhard

(06-25-2015 10:01 PM)PANAMATIK Wrote: [ -> ]I ordered some display modules in germany for this project. They have the same price than in US but in Euro.

I don't want to sell the bare boards. First I made a mistake as described above and the assembly is somewhat special. Second I will at least get some benefit for going on with these works.

Therefore I offer the assembled boards for 30 Euro + shipping. The components are 10 Euro, the board is another 10, and the rest is intended to keep me happy You could spare 10 Euro with the bare boards, but ...

If you want to order please PM or mail, I can deliver from tomorrow.

Bernhard

OK, sorry, I am not interested in complete boards. As I stated I have already some displays (HP 5082-7414, same pin-out as QDSP6064).

On the Commodore's:
The P-50 and PR-100 also have 14 digit units but only use 12.
Others like the 4190 use all 14 digits. For these I have purchased 3-digit displays to build up 14 digits using 2x 3-digit + 2x 4-digit modules.

I will probably design my own PCB and see if I can make one board to accommodate both 12 and 14 digits by mounting different number of LED modules (possibly with some "jumper" pads for the different configurations) - it would be a waste to use the rather more scarce 3-digit modules in units that don't need them.

It is just that this has been a "to-do" for quite some time now .

Best regards.

LED module is available again!

The new LED displays for Woodstock calculators were out of stock now for more than 2 years. I could find a quantity of the bubble display modules again and can offer a limited stock for the HP LED display modules.

Unfortunately the price of the modules has increased significantly. A single module is offered from 20$ to 45$ and the display needs three of them.

Nevertheless I hope it will repair some defectives Woodstocks for you.

Woodstock LED repair kit

Bernhard

Hackaday posted this article recently.
I wonder if it holds the future for replacement LEDs in Woodstock calculators.


https://hackaday.com/2021/02/08/a-modern...1-display/

(02-10-2021 12:50 AM)Ren Wrote: [ -> ]Hackaday posted this article recently.
I wonder if it holds the future for replacement LEDs in Woodstock calculators.


https://hackaday.com/2021/02/08/a-modern...1-display/

They would be too large to fit in the space plus the drivers would need extensive work, and I also believe they are a bit current hungry.

I'm sure if a company made a million or so 5 digit bubble led modules, they wouldn't last that long once word got around of them being available at a good price.

cheers

Tony

I asked myself similar questions regarding HP97 display issues.

And i found those 14 segments old HP displays still in stock :

https://fr.aliexpress.com/item/326040040...npKt8&mp=1

Could the be adapted to a 97 with its new Teenix MB ?
=> it would then be possible to display alphanumerical text aka the HP41C

(02-10-2021 07:37 AM)Chr Yoko Wrote: [ -> ]I asked myself similar questions regarding HP97 display issues.

And i found those 14 segments old HP displays still in stock :

https://fr.aliexpress.com/item/326040040...npKt8&mp=1

Could the be adapted to a 97 with its new Teenix MB ?
=> it would then be possible to display alphanumerical text aka the HP41C

I don't think so, the CPU replacement still relies on the original display drivers.
I think these also need software driver to interact with, and they can draw up to 90mA each, x 4 = 360mA :-(.

cheers

Tony

(02-10-2021 08:23 AM)teenix Wrote: [ -> ]I don't think so, the CPU replacement still relies on the original display drivers.
I think these also need software driver to interact with, and they can draw up to 90mA each, x 4 = 360mA :-(.

cheers

Tony

Correct about the actual display that is hooked to the keyboard/display separate board and its LED driver ships (maybe some kind of "shift registers" ?)....

But it maybe possible to bypass that original HP driver board and connect the new display & its modern driver directly to the HP97 CPU MB ?

As for the 360mA, the HP97 is a table/transportable calculator more or less hooked to a power supply and running on a quite large battery pack.
Also maybe it just needs to shut the LEDs off longer while printing so save on mAs ?

(02-10-2021 09:47 AM)Chr Yoko Wrote: [ -> ]But it maybe possible to bypass that original HP driver board and connect the new display & its modern driver directly to the HP97 CPU MB ?

It gets a bit more complicated though because the key scanning is also done from the display driver.

But all things are possible, well .....nearly :-)

PS, the printer and card reader models turn the display off when those items are working.

cheers

Tony