A2e cassette interface not working, missing -5V

2 replies [Last post]
Offline
Joined: Mar 1 2014
Posts: 2

Dear Apple Users,

I am experiencing a strange problem with my new Apple IIe (PAL) 64k.

Currently, there are no expansion cards installed.

When I try to load a program from tape (BASIC "LOAD" command or from
Machine language monitor), nothing happens, there is no beep which
should come after receiving the program header.

I tried cassette recorder or PC soundcard.

The output level is +/-1V peak to peak (checked with an oscilloscope, see annex).

Writing programs to cassette interface works fine.

First thing I tried was checking the power supply voltages (they are
fine without load).

But connected to the system board, the -5V (VEE) voltage rises to
+3.01V.

I assumed a failure of the cassette interface op amp (I have a MC 4558
installed, not an 741, see schematic in annex).

Removal/Exchange of the op amp has no influence on the failure.

The rest of the apple works fine, as far as I can test at the moment
without software, except for the video output, which is very crippled.

A 80C card gives fine video output.

I would be very happy if someone could give me an advice,

thanks a lot and best regards
Stephan

AttachmentSize
oszi.jpg12.45 KB
cass.jpg73.57 KB

Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.
spicybeef's picture
Offline
Joined: Mar 13 2014
Posts: 4
Re: A2e cassette interface not working, missing -5V

Why is an MC4558 installed? It is not pin compatible with the LM741 op-amp. MC4558 is a dual op-amp in an 8-pin DIP package and the LM741 is a single op-amp in an 8-pin DIP package. Same package but different insides. Put an LM741 back in place and I am betting it will work again.

See the following:

MC4558 pinout: http://circuits.datasheetdir.com/37/UTC-MC4558-pinout.jpg
LM741 pinout: http://www.learningaboutelectronics.com/images/LM741_pinout_diagram.jpg

Offline
Joined: Mar 1 2014
Posts: 2
Re: A2e cassette interface not working, missing -5V

Hi spicybeef!

Thanks a lot for the reply! I am aware of the different pinouts of the Op Amps.
I am relatively sure that the MC4588 is the original assembly (because the board does
not look like being repaired) and I am convinved that the cassette interface worked a few
years ago with the 4588 in place.

And, for me the most important point: the -5 Volt is missing even if no Op Amp is in the board, which
is for me an indication that there is something different wrong.

Are you really sure that there is no chance that there are original IIe boards with MC4588 installed
in original configuration outside?

Otherwise, do you think I could make things worse by trying an 741?

Thanks and best regards
Stephan