Repurposing a spare Thurlby LA-160B Logic analyser.

[djsb]

I have a 2 off 1980's vintage Thurlby LA-160B logic analysers. These use the Rockwell R6502P CPU. I have one that works at 240v and 10 MHz, which I'm going to use for its original purpose. The spare one is a 120v model, which only has a different mains transformer and a 20 MHz crystal. I'm going to swap the 2 off M2764A ROM chips and crystals, as the 120v is a type B (20MHz) and the 240v is a type A (10MHz). They both have extended capabilities option ROM's (same M2764A type ROM's). Alternatively, depending on finding out that more components need swapping I MIGHT just swap the mains transformers over. I'm also fitting a couple of new 2.4v batteries.
First, is it easy to back up the ROM chip's contents (I have an XGecu T48 programmer)? I'm assuming that they are in intel HEX format?
I'm wondering if the spare one can be repurposed and made into a simple SBC (it has an 8 x 4 keypad matrix and an 8 digit LED display). I have attached the service manual, which contains the schematics. I have asked Aim/TTI if I have their permission to recreate the schematic using KiCad (may not need it, but I've asked them anyway). What are your thoughts? Thanks.

David.

[Dr Jefyll]

Wow! What a charming example of 20th Century, retro technology! Can we see some photos, please?

Also, my advice is to hold off on swapping any parts or repurposing one of the units, at least until we can ensure a good understanding of the obstacles and potential rewards involved.

-- Jeff

[djsb]

I've not got any of my own photo's at the moment, but here is a page giving an overview of the UK model (and a further link to more detail)

https://sonicsheep.com/Electronics/2-Th ... LA160.html

The one from the USA is the Interplex IE1620 which was made in the UK but exported. This one has a 120V transformer and is an LA-160B 20MHz model. Other than that, it's essentially the same (apart from faster chips and a 20MHz crystal and a later revision board). As it's 120V, I've not been able to turn it on yet.

https://www.ebay.co.uk/itm/225092768810

It looks like I'll be swapping the 240V transformer into the IE1620. There are too many parts that would need swapping over. I want to keep the UK model as close to original as possible, apart from the transformer.

[GARTHWILSON]

That sounds like a really fun project!

djsb wrote:

The spare one is a 120v model, which only has a different mains transformer

Things like this, offered in different voltages, usually have the same transformer, but with two primary windings, and the input voltage is selected by how they're wired, the 110V one having them in parallel, and the 220V one having them in series.  You might not need to change the transformer, only how it's wired.

Quote:

First, is it easy to back up the ROM chip's contents (I have an XGecu T48 programmer)?

It's always a good idea to read these old EPROMs right away and make backup files before the EPROMs gradually erase themselves over the decades.  I have never seen one lose its data; but the fact is they were only guaranteed to hold it for ten years.  The many years beyond that are just bonus.

Quote:

I'm assuming that they are in intel HEX format?

Intel Hex is a format handled by device programmers.  The two most commonly used ones are probably Intel Hex and Motorola S-Record.  The EPROM itself doesn't know or care what format was used to store the data on disc or transfer it between the PC and the programmer.  When you read the EPROM to make a backup file, you'll probably choose, at that time, what file format to use, or the programmer may default to one if you don't choose.

[Dr Jefyll]

On the schematic, this dot seems to imply that the transformer primary is, as Garth suggested, divided into two segments as a means of accepting either 120V or 240V.

Even if this proves not to be the case, there are other ways of managing the voltage issue. If I were in your place I'd be reluctant to resort to a transformer swap between the two units.

-- Jeff

[djsb]

Thanks for your replies. I'll do a visual inspection first to see if there are any wiring differences between the two transformers. I'll then try to examine the windings with my multimeter (resistance measurements first for safety reasons) via a few clip on/soldered on wires. I may be lucky and ALL the transformer pins may be attached to the PCB, but may be routed differently between the interplex and the Thandar models. If I can't manage this I'll VERY carefully remove the transformers as there is very limited space to examine the transformer wiring in situ. As these are older PCB's I may be fortunate in NOT having to deal with plated through holes for the terminals (as used in modern PCB's).The user manual and service manual is very specific that the transformer primary winding voltage is NOT selectable.
Worth a look though, just in case the schematic is incorrect. I'm curious, what else can I try? Thanks.

[djsb]

I can confirm that the transformers on the 2 devices are different. The additional tap on the primary is for 110v/120v on the interplex and 230v/240v on the Thurlby models.
The resistance values are as follows:
PRIMARY WINDING
LA-160 357.4R and 325.6R 240V/230V
IE1620 40.6R and 37R 120V/110V

SECONDARY WINDINGS
LA-160 WINDING 1: 0.7R WINDING 2: 3.9R WINDING 3: 7.6R
IE1620 WINDING 1: 0.5R WINDING 2: 2.6R WINDING 3: 3.4R

I'm going to measure the voltages on the secondaries with the 240v and 120v present (I have an external 240v to 120v transformer for this) and confirm that they are the same.