8 Apr
2004
8 Apr
'04
12:09 p.m.
In message <m1BBLYF-000JAXC@p850ug1>
ard(a)p850ug1.demon.co.uk (Tony Duell) wrote:
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...
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 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