Hello

I'm working on this old touch-tone telephone (Statesman 9040R - see picture). I'm essentially building a new circuit from scratch - it won't be connected to the phone lines but will instead be an arduino based interactive playback circuit.
I would still like to understand how the old circuit works and so far I feel comfortable that I have identified a lot of the major components and how they all connect and work together.

However, I haven't been able to find any information about the largest IC on the board. I know it is doing DTMF generation as it connects to the rows and columns of the keypad, as well as the speaker in the phone handset.

The IC has the following text printed on it:
MEDL JMA528PD S8547

I can't find any useful information online about it, and I can't quite work out what the rest of the pins are actually doing.

My main curiosity is how the phone line signal makes its way to the handset from the network, as it looks like the handset speaker only connects to this IC, and so the IC must somehow also pass the phone signal as well as the DTMF tones. I'm sure part of this comes down to my ignorance about telecoms and phone lines etc.

Any help in identifying this IC is greatly appreciated (photos attached)!

 

After a lot of digging through datasheet archives I found it!

In case this ends up being useful to anyone, my process was as follows:
- Found out that 'MEDL' is short for Marconi Electronic Devices, and searching 'Marconi' instead of 'MEDL' gave me far more relevant results
- Looked for Marconi datasheets that mentioned DTMF on datasheetarchive.com
- I noticed there were a lot of dialler or DTMF ICs, but they were all in the 'MA' family (e.g MA531), and so the text on my IC 'JMA528' might actually be listed under 'MA528'
- searched different keywords etc until I eventually found the MA528 datasheet
- compared datasheet pinout with what I managed to work out from the circuitboard and it's a match!

Attaching datasheet - I don't imagine this specific case is useful to that many people but worth sharing results

 

As you discovered: MEDL = Marconi Electronic Devices Ltd
S8547 is manufacturing date - week 47, 1985. The 'S' may indicate the fabrication house where it was made.

"Semiconductor operations were first established at Lincoln in 1956 when British Thomson Houston Ltd (BTH) purchased land and buildings. [...] In 1963 the site was name changed to Associated Electrical Industries (AEI) and probably to GEC around the late 60’s. In 1980 the site became Marconi Electronic Devices Ltd (MEDL) and again in 1990 the site was under the banner of GEC Plessey Semiconductors."

I used to work at Plessey in the 1980s on telecom equipment and visited MEDL at Lincoln on a number of occasions to talk to chip designers on their products, though not that specific device as I recall.

As you surmised, the IC handles voice as well as DTMF signalling, and does the echo-cancelling (side tone suppression) electronically rather than electromagnetically as per early equipment.

 

As you discovered: MEDL = Marconi Electronic Devices Ltd
S8547 is manufacturing date - week 47, 1985. The 'S' may indicate the fabrication house where it was made.

"Semiconductor operations were first established at Lincoln in 1956 when British Thomson Houston Ltd (BTH) purchased land and buildings. [...] In 1963 the site was name changed to Associated Electrical Industries (AEI) and probably to GEC around the late 60’s. In 1980 the site became Marconi Electronic Devices Ltd (MEDL) and again in 1990 the site was under the banner of GEC Plessey Semiconductors."

I used to work at Plessey in the 1980s on telecom equipment and visited MEDL at Lincoln on a number of occasions to talk to chip designers on their products, though not that specific device as I recall.

As you surmised, the IC handles voice as well as DTMF signalling, and does the echo-cancelling (side tone suppression) electronically rather than electromagnetically as per early equipment.

Thanks Irving - that's lots of really interesting insight!

 

I don't see any mention of touch-tone on the datasheet. Perhaps that's a pulse dialer chip (with memory)?

 

I don't see any mention of touch-tone on the datasheet. Perhaps that's a pulse dialer chip (with memory)?

Ah you're totally right - I was completely blind to that! And actually looking a bit deeper it seems like the 9040R was a pulse dialler so that makes sense! For some reason I was assuming it was touch tone... Oh well I'm going to rebuild it as touch-tone regardless as that seems more suitable for my application

Thankyou for pointing that out!