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Schneider cpc 464/ strange issue with basic

Started by jpx13, 19:55, 22 April 17

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jpx13

Hello !

I've been reading all the topics in the hardware section without finding an answer to my problem...
I purchased on the bay a clean schneider cpc 464 that seems to work at first sight...BUT it has a strange issue i can't explain:

It just powers up fine, and i get the ready prompt.

When i try to write a BASIC program to draw lines, or plot something, it just runs fine, and does what it is supposed to.
But it is impossible to use the PRINT function ??!!??  I explain what i get in that case:
If i try to type the simple PRINT "Hello World", the computer displays 3 lines of garbage with strange signs, then the speaker beeps, and another batch of garbage in a vertical line on the right of the monitor... After a few seconds, I can see the prompt with "ready" in a vertical fashion on the right !

If I reboot, it gets normal, but I can't type in print...

i tried PRINT FRE(""), and I get a result, but it's only signs and not numbers...

If I say A=5, and type PRINT A, the result is two signs but not the expected result, nor letters...

If you have an idea of what it could be ?

It is strange that I typed 30 lines of code to draw lines, plot points without problem, but can't print anything !

I already opened the case, everything was clean inside...

Any help would be appreciated.

Thanks !

Bryce

I'd try replacing the BASIC ROM and see if that helps. If you know someone who owns a LowerROM board you could test this before getting the soldering iron out.

Bryce.

jpx13

Thank you for your reply Bryce, I was affraid it could be something like this... Involving de-soldering a chip on the board !

I have read it was possible to replace the ROM with an Eprom flashed with the firmware, but I don't have the necessary tools to do so.

A lower Rom board is an extension you plug in the computer   ? Or under a chip on the MoBo ?

Do yout think it could be memory related (i mean Dram) ? With some parts of the Basic loaded in ram being corrupted because of partially bad ram chip(s).
Is it possible to check all the RAM with a simple method, or by typing in a program in Basic that would fill the memory?

For further investigation, I tried to load a program from a tape, but it seems to begin the loading (block1, Block2) then the computer crashes with one of my tape (an original game).

With the other tape I recorded from a downloaded tape file converted to WAV, It starts loading, I can see a picture slowly being displayed on the screen, but at some moment, the tape recorder stops then restart in the middle of the download (I mean when I can hear the stream of bytes) and it does not load the program to the end.

Finally, I tried saving to a blank tape a short program I wrote earlier, but to no avail, because of bad recording quality (the sound is not steady when you hear the tape) the computer can not load the program just saved...

Again  many thanks for your help, I would really be pleased if I could bring it back to full functionnality...

JP


||C|-|E||

I don´t think you have a RAM problem, but I would suspect the ROM all the way. As Bryce said with a lower ROM board (something like this: http://www.cpcwiki.eu/index.php/LowerROM ) you could test it very easily and yes, it is something you can plug to the computer  :) . Replacing an IC is not the end of the world either, just send the computer to somebody that can do it if you are not sure about your skills  :)

Bryce

It's not a RAM issue. The 464 has 8 RAM ICs, but they are 64Kx 1bit RAMs. This means that each RAM holds one bit of every address, so if a RAM is bad ALL RAM addresses will have a problem and the computer won't boot.
Yes, a LowerROM Board is an extension that plugs onto the back of the CPC. I could lend you one, but if you can't solder then it's not going to be of much use. If you like, you can send me the PCB and I will do the repair for you.

Bryce.

jpx13

Hello,

Bryce,||C|-|E||, I agree with you, if the RAM chips are 64x1, a bad chip would crash all the RAM...

I am able to solder, I am reasonably well equiped (multimeter, power supply, small Scope...), what I can't do is to flash an Eprom, because I don't have the equipement...

Your offer to lend me a Lower ROM board is appreciated. Another possibility would be to try a new ROM (I mean an eprom flashed with the good firmware) without testing with the ROM Board ?  It should not be so expensive for a 32 K Eprom ?

Do you have the possibility to flash an Eprom and to send it to me ? Of course I would pay for the costs involved.

Again thank you for your replies, maybe with your help my CPC could be fixed !

JP

||C|-|E||

I am sure that Bryce can burn an EPROM for you  :)

Bryce

Yup, send me a PM and I can organise an EPROM for you.

Bryce.


jpx13

Hello,

Thanks to Bryce, my new Eprom arrived today, I'll report the result after doing my homework  ;D with the soldering iron...

JP

jpx13


Homework done... Not the prettiest soldering job, but it's done ! ::)

And now, it WORKS !!! ;D ;D ;D

Thank you Bryce, and|C|-|E|| ,  you were right !

Another CPC back to life. I will now have a look at my Datacorder wich needs attention (not able to save properly, bad sound quality when recording)

By now, I have soldered an audio input on the read head wiring of the datacorder, and use TapDancer on an old Android phone, it works wonderfully !


JP

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