IBM Engineers

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Thu Apr 8 19:09:13 2004

>
> In message <m1BBLYF-000JAXC_at_p850ug1>
> ard_at_p850ug1.demon.co.uk (Tony Duell) wrote:
>
> > Reminds me of the time a system manager at a place I was working ordered
> > a failed servoid off the site. He wanted to replace every PCB in some
> > expensive piece of equipment because they all failed diagnositcs. I'd
> > just turned up, slapped a meter on the 5V line and found it was sitting
> > at 4.2V....
> I've seen that happen. I (once) tried to repair a DIY speech synthesiser; it

The PSU problem I mentioned was actually due (as ever) to dried-up
electrolytics on the output side of the PSU. Yes, I ended up having to
fix it...

> was suffering from the standard "it worked one minute and now it's dead"
> problem. Vcc was at 2.1V (it was supposed to be 5V +/- 5%). I pulled the
> SPO256 and powered up without it and the Vcc came up to 5V. Replaced the '256
> and the Vcc plummeted again. Turns out there was a solder whisker on the
> board, between a Vcc track and a GND track. Pushing the chip in flexed a
> track slightly and moved the whisker into place over the tracks - removing

Evil!!!!

> the chip allowed the whisker to move back and short the power bus. That
> whisker took me a good half hour to track down - it was thinner than a strand
> of wire-wrap wire. Of course, after I fixed the synth, I leaned over to plug
> the interface connector in... and shorted out the PSU's output connector.
> That did plenty of damage to the PSU, which still needs rebuilding. *sigh*
> OTOH, I've still got a few SPO256es - all working. I just need some 3.12MHz
> crystals for them. No, the SPO256es are not for sale :)

I used to use 3MHz xtals (available from RS components). Gave a somewhat
low-pitched output, but it was useable. Most SPO256s will work at
3.2768MHz, which is another easy-to-find xtal frequency. Finding 3.12MHz
xtals was almost imposible in my experience...

I have at least one CTS256 chip in stock. This is a programmed
microctroller (TMS7000/PIC7000 series IIRC) that connects to an SPO256
and which does text-to-speech conversions. It takes a serial or parallel
ASCII input IIRC. I used one for the IMS (Interactive message system)
terminal for my CoCo 2 that I had on my door as a student so people could
leave me messages (the speech syntheiser for output and the keyboard from
an Atari 400 -- selected as there were no keycaps to get 'borrowed' for
input).

Of course the CoCo's own speech/sound cartridge contains an SPO256, an
AY-3-891x (I thin 8913, but I would have to find the schematics) and a
microcontroller (8048 I think) which does both text-to-speech and allows
you to control the AY-3-8913 sound chip. Interesting design...

-tony
Received on Thu Apr 08 2004 - 19:09:13 BST