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IBM 5150 - 131 error

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dongfeng

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I have a bunch of dead 5150 motherboards, so I thought that I would try and fix some of them. On one, I noticed that component TD2 (black rectangular thing) had snapped off, so I soldered on a replacement from a known dead board. After a few faulty memory chips (now solved), I have a working 5150 motherboard with a full 256kB memory! :mrgreen:

However, I am getting a 131 error on POST, which I believe means "Cassette wrap test failed". I doesn't stop the machine from working (and I'm unlikely to use the cassette anyway), but it would be nice to fix it if possible. Any suggestions? :)
 
anything I could help you with would come from this book so DL it and take a look!

http://www.vintageibm5150.com/docs/HMS_202.zip


dongfeng said:
I have a bunch of dead 5150 motherboards, so I thought that I would try and fix some of them. On one, I noticed that component TD2 (black rectangular thing) had snapped off, so I soldered on a replacement from a known dead board. After a few faulty memory chips (now solved), I have a working 5150 motherboard with a full 256kB memory! :mrgreen:

However, I am getting a 131 error on POST, which I believe means "Cassette wrap test failed". I doesn't stop the machine from working (and I'm unlikely to use the cassette anyway), but it would be nice to fix it if possible. Any suggestions? :)
Click to expand...
 
Have you a wrap plug connected to the cassette port? (probably just a link from play in to record out) I would suspect not, and that would probably explain the error!
 
frozenfire75i said:
anything I could help you with would come from this book so DL it and take a look!

http://www.vintageibm5150.com/docs/HMS_202.zip
Click to expand...

Nice one, thank you!!!


nige the hippy said:
Have you a wrap plug connected to the cassette port? (probably just a link from play in to record out) I would suspect not, and that would probably explain the error!
Click to expand...

You mean connected to the cassette port? There is nothing connected to it. My other 5150 does not have anything connected there, and that works fine...

I also have a problem that it gives a 'Parity Check 1' error message whenever the final bank (bank 3) is filled with memory. No matter if I swap the memory to a known good set, it keeps appearing. Works fine in 192kB though.
 
The "cassette wrap test" is similar to the internal loopback test in a UART. It's internal - you don't need a loopback (wrap) plug.

When the cassette interface is not in use, the relay on the motherboard is 'unactivated'. With the relay in that state, the relay loops (wraps) the cassette DATA OUT signal (at 'full strength') to the circuitry that processes the cassette DATA IN signal.

During the POST, the "Cassette data wrap test" puts the relay into the 'unactivated' state, then generates some cassette DATA OUT signal, expecting (because of the loopback) to see that same signal coming in on the cassette DATA IN line. Failure to see the same signal results in the POST posting a 131 error.

The relay on your faulty board may have a set of contacts stuck in the 'normally open' state. Try lightly tapping the relay using the end of a screwdriver. The relay is adjacent to the cassette connector and is designated K1.
 
Jumper P4

Jumper P4

At the front of the motherboard is jumper P4 - the only jumper on a 5150 motherboard. As detailed in the 5150 Technical Reference, the jumper is either set M-C or A-C, and it controls the amplitude of the cassette DATA OUT signal that goes to the cassette DIN connector.

When the jumper is correctly set (either M-C or A-C), it does not affect the amplitude of the cassette DATA OUT signal that is looped back to the cassette DATA IN circuitry.

However, if the jumper is incorrectly positioned M-A, that shorts out a resistor resulting in a degraded signal being looped back to the cassette DATA IN circuitry. That COULD be the cause of the 131 error. I'm not willing to experiment of one of my 5150s to see if it's a definite.
 
missing −5V

missing −5V

A missing −5V power supply line is one of the reasons why the 131 POST code (Cassette Wrap Test) may be displayed.
 
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