Re: Tape port trouble on a PET 2001N

From: Marko Mäkelä (
Date: 2002-11-10 19:56:56


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In your table, does "TAP" mean the Commodore C2N datasette or an empty port?
Did you measure the voltages for an empty port?  At any rate, I think that
the problem can be corrected by changing the firmware so that the lines are
configured as inputs.


From: "Juergen Sievers" <>
To: Marko Mäkelä <>
Cc: <>
Subject:  Re: Tape port trouble on a PET 2001N
Importance: Normal
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Dears Marko and cbm friends.

At the first I want to  say many thanks to Marko. Marko you are very kind
and much helpfully "hardware dealer++".
Many thanks Marko.

And now the result of the measurement I did in reflection on your hints -
see quotings below.

Tapeconnector	Port I (backplane)   Port II (inside)
Signal/Pin         connected was       connected was
------------------ TAP ---- C2N232-----TAP----C2N232
Sense 6-F          +2V      +3,5V      +4,5V  +5V
Write 5-E          +5V      +5V        +5V    +5V
Read  4-D          0V       +5V        0V     +5V   !!!!!!!
Motor 3-C          0V       +7,5V      0V     +0V
Vcc	2-B          +5V      +5V        +5V    +5V
GND	1-A          GND      GND        GND    GND

That was it I measured and it seems to me the read port are short to the
write port (4-D).
But I don't know why this has the portrayal effect only on the first port.

The second divergence (3-C) may by the motor has being on during the

[ Removed private and unauthorised message part ]

> ----- Forwarded message from William Levak <> -----
> From: William Levak <>
> To:

> It sounds like you have a short on the cassette port.  Probably one
The connector fits fine and I can tell you that for certain, there had been
no hard short if the C2N232 was plugged in.

> of the transistors that drive the port (Q4, Q5, Q6), the voltage
> regulator (VR2), or capacitor (C70).  Since the operating conditions are
> different, a marginal component may behave differently.

The most miracle is:
if the C2N232 had been connected to the backplane first few times then the
machine's  monitor program was coming up.
Now, a few times later, always the normal system prompt appears on the
screen and only the topmost line of keys will cause some action if pressed.
Not the right key letters, only some cryptic stuff but always only at any
keys from the top keyboard line.

> There may also be a marginal short on the connector or circuit traces.
> Another, simpler  possibility is that the connector does not line up
> correctly with the card edge.

I test this and it isn't the reason.

> On Sat, 9 Nov 2002, Marko Mäkelä wrote:
> > I recently sold a C2N232 interface to someone in Germany.  When he plugged
> > it into cassette port #1, the computer crashed and sometimes went to the
> > machine language monitor.  A normal tape drive works in both ports, but
> > the C2N232 only works in port #2.  Does anyone have an explanation?
> >
> > The computer is a North American PET2001N32, and he uses it with a 220->110
> > volt transformer that has enough wattage (400 VA).  The only electrical
> > differences between the C2N232 and the tape drive should be that the C2N232
> > takes some power from the +5V line all the time, while the tape drive might
> > not, and that the cassette motor power line is not connected to the C2N232.
> >
> > 	Marko

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