Good haul of old pc stuph

Tony Duell ard at
Sun Dec 18 16:59:21 CST 2005

> Tony Duell wrote:
> > The really bad one in my experience is the CTR-80. This was supplied 
> > with some Model 1's and had a really nasty design bug. When turned off by 
> > the remote socket _in play mode_, the erase head would put a glitch on 
> > the tape.
> How do design glitches like that get past QA?  (Or was there no QA?)

Rememeber the CTR-80 wasn't designed for computer use. Maybe it was less 
serious on an audio recording (although the 'thump' was certainly audible!).

> One thing I love about my old IBM PC 5150 with ST-225 is that *it is still 
> running 22 years later*.  I fire it up at least once a week to do some hobby 

Newcommer :-). My 32-year-old HP9830 still fires up. I've had to solder 
one kludgewire on a RAM board to repair a damaged track, and had to 
replace a couple of TTL chips in the processor. 

And of course my HP9100B calculators still work, although I've had to 
replace the odd transistor in those.

> programing or game playing and the damn thing just runs.  I can't say that for 
> my modern machines -- I had an ATX power supply die on my twice in 5 years 
> (had a 5 year warranty), and I've had modern drives fail quite spectacularly, 
> etc., etc. but I've been spoiled by most of my old machines.  They just work.

Yes, these machines were designed to last, were designed to be repaired 
(I was pointing out to a friend earlier today that the older machines had 
labelled testpoints and adjustments, etc). And they were much less 'built 
to a price' than the machines today.

> I mention all the above because it was a surprise to hear that a piece of old 
> consumer-level hardware had such a nasty flaw.
> > The work-around was to pull the remote-control plug and use it in manual 
> > control mode only. The fix, IIRC, was to solder a 10uF capacitor in 
> > parallel with the erase head.
> Confused -- why would that fix it?

I beleive this thing used DC erase -- that is that the erase head was 
simply connected to a DC supply and became a permanent magnet in record 
mode. I can't rememebr how the glitch got to the head (maybe via 
decoupling capacitors, or something) in play mode, but connecting this 
capacitor in parallel with the head significantly reduced it.

Incidentally, the Radio Shack cassette recorder I had the most success 
with for computer applications was a little white one, ran off 4 AA cells 
or a mains adapter (no built-in mains PSU), had a click-stop on the 
volume control that gave a good output level for most computers, and had 
a 3 position slide switch to over-ride the remote control input. I forget 
the model number.


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