Author Topic: CPC 464 -- all basic commands result in Syntax Error & a pinched y  (Read 1180 times)

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Offline thomas

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Hi There!

I'm trying to revive my "Schneider" CPC from '84. It boots up, but I cannot issue (basic) commands.  Every command gives me a "syntax error".

What's also odd:
- the "y" character has a hole
- pressing ESC reboots the machine (is this normal?)- pressing "key up" (in the area with the "copy"-key) prints "fat up arrows" (is this normal?)

My experience with Amstrad is very little and besides a video cable I do not own any peripherals or software (but a Dandanator is on it's way).

Things I tried so far:
- cleaned everything up, including kbd membrane
- reflowed solder joints around RAM chips
- reinserted the two socketed chips (z80 + 40010)
- searched for broken traces and cold solder joints (magnifying glass, sunlight)
All ICs stay kinda cool.Board has PT No. Z70200.

if I had to guess, I'd say it's a bad ROM; with faulty RAM, it wouldn't even boot, right?
Any help would be greatly apreciated!
- thomas
« Last Edit: 18:02, 15 February 21 by thomas »

Offline GUNHED

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Looks like the lower ROM has problems / is corrupted. Should be easy to change (you can use an EPROM).
http://futureos.de --> Get the revolutionary FutureOS (Recent update: 2021.01.24)
http://futureos.cpc-live.com/files/LambdaSpeak_RSX_by_TFM.zip --> Get the RSX-ROM for LambdaSpeak :-) (Updated: 2021.05.24)

Offline thomas

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Thank you!

Just to make sure: the ROM is the 400007?
- thomas

Offline Audronic

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@thomas


No NOT the 40007


The ROM is 40009 (Left hand side )


Keep Safe


Ray
Procrastinators Unite,
If it Ain't Broke PLEASE Don't Fix it.
I keep telling you I am Not Pedantic.
As I Live " Down Under " I Take my Gravity Tablets and Wear my Magnetic Boots to Keep me from Falling off.

Offline thomas

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 :doh: ah yes -- I meant it! :-) The 40009 below the sond chip. Sorry!
- thomas

Offline thomas

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got a Dandanator and some of the preinstalled games run just fine! :-)
Now, I will have to wait for the equipment to arrive needed to burn and replace the bad ROM.  :-)

- thomas

Offline Gryzor

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Will no one mention the black and white mode? :D

Offline thomas

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hm yes ... I don't know why it is B/W. Using a cheap (Amazon, 20 €) SCART to digital converter which I blamed for the B/W picture. (?)
Hopefully it's not another fault of the machine (Chroma gone?). Any ideas on how to chase that problem are welcome! :-)
- thomas

Offline Bryce

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hm yes ... I don't know why it is B/W. Using a cheap (Amazon, 20 €) SCART to digital converter which I blamed for the B/W picture. (?)
Hopefully it's not another fault of the machine (Chroma gone?). Any ideas on how to chase that problem are welcome! :-)
- thomas

No chasing required, your diagnosis in the first sentence is most likely correct. There's another active thread here discussing / recommending which convertors work best. Yours most likely only converts the composite signal.

Bryce.

Offline thomas

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thank you Bryce! :-)

Offline thomas

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Morning!

Another minor problem: there is no Sound from internal speaker. Measured the resistance of the rotary knob between 8 and 12 Ohm.

I found some yellow stuff underneath a cap on the cassette PCB. First thought this would be leakage, but it is most probably some glue.

I'm kind of lost here, so if anyone can share some ideas how to debug that issue go ahead! :-)


Offline thomas

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what's nagging me more than the int. speaker: I replaced the ultra cheap Scart to HDMI box with one a little less cheap and RGB capability.
Color is good, but the picture is kind of "jumpy" (every other second it "jumps" to the left, next second it centers back; there seems to be some noise too).
Maybe a synchronization problem?

Waiting for a SCART cable for the C64 so I can test the upscaler with a different machine.
- thoma

Offline Animalgril987

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It wouldn't hurt to replace that cap, just in case.

Offline thomas

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YESS!!! :-)
After replacing this suspicious 22 micro cap and the "fat" one (C322, 470 micro) which had some "glue" underneath as well (but I guess it was ok) on the cassette PCB internal sound is working again! Yeah!

One down, (at least) two to go:
- replace the bad (?) ROM (waiting for a TL866II)

- figure out what's wrong with the sync signal; checked the traces for conductivity, lowered resistance of 317 to about 150 Ohm, everything seems OK. I guess my (new) converter box is not good enough for the Schneider (no problems with a C64, though); ordered a different upscaler, let's see if this will sync correctly
thomas

Offline Bryce

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YESS!!! :-)
After replacing this suspicious 22 micro cap and the "fat" one (C322, 470 micro) which had some "glue" underneath as well (but I guess it was ok) on the cassette PCB internal sound is working again! Yeah!

One down, (at least) two to go:
- replace the bad (?) ROM (waiting for a TL866II)

- figure out what's wrong with the sync signal; checked the traces for conductivity, lowered resistance of 317 to about 150 Ohm, everything seems OK. I guess my (new) converter box is not good enough for the Schneider (no problems with a C64, though); ordered a different upscaler, let's see if this will sync correctly
thomas

The C64 outputs a composite video or S-Video signal, the CPC outputs an RGB signal. Just because a converter works with a C64 is no guarantee that it will work with a CPC.

Bryce.

Offline thomas

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yes you're right .... (I forgot EVERYTHING about the different options for color output in the old days and just slowly regain some knowledge about RGB vs. Composite etc.  ... guess HDMI spoiled me somehow ...).   :o
Well, let's see if the new upscaler will fix my sync issue, people were prasing it for the Amiga (which has RGB as well, this time I'm certain! :-)
I also have one of the GBS 80-something boards (the newer model with HDMI out), but no means to connect it to the CPC at the moment.

- thomas

Offline thomas

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small improvement: printed some cassette reset button replacements (available on thingiverse). They work quite nice!

Offline thomas

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ok, so I investigated a little further and invested in a CPC 6128! :-)
(yeah I know, my retro computing hobby slowly escalates, but the Missus is still tolerant ...)
I figured that some "flakeiness" with the Scart converters is quite normal with Amstrad machines and the 6128 shows similar behaviour.
Ordered an "active" cable, let's see if this improves picture stability.

But it is not a "fault" of the 464.

I'm not yet 100% convinced that some of my problems with the cpc aren't caused by a bad Gate Array, but I keep praying it is ok. (for example, I cannot start the RAM test on the Dandanator!).

Next step would be to put the 6128's 40010 into the 464 and see if this changes anything. And I'll remove the Centronics connector for the cartridge port of the 6128 to see what the Dandanator would do with a fully working machine.

Gettin' there, I guess. I'll keep you posted!
- thomas

Offline Bryce

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I'd suggest swapping the Z80 from the 6128 first to see if that's the issue.

Bryce.

Offline thomas

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Hope it is ok if I share some more thoughts.

- replaced the z80 with a known working one, makes no difference

- remember, the up arrow behaves sort of wierd, since it does not place the cursor in the line above, but prints a "fat up arrow"


- checked the schematics/service manual, and the following keys are in the same row:  cursor up, cursor right, cursor down, 9, 6, 3 and ENTER


To sort out a defect membrane, I connected the 6128's kb with the 464 -- same behaviour.  But this COULD explain that <Basic Command> + Enter results in a syntax error? Don't know. If yes, the 74SL145 (IC 101 in the schematics) could be bad
What's also wierd:

print 1+2

etc. => syntax error
But

?1+2
prints 1! (not 3, though).

And:

?(1+2) => syntax error.

- checked all other characters, the small "y" is the only one with a hole ("hole in the y").

Did not dare yet to test the 40010 of the working CPC in the non-working CPC, since if I don't really take care and concentrate, I could end up with 2 fried machines ...


thomas



Offline thomas

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ah, and bkspc pressed twice => beep! This is a good sign, I guess!

Offline thomas

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hm, ok "row 9" of the kbd matrix is connected to the AY. Maybe a fault there, but otherwise sound is working.

Offline thomas

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ok, a small update:
I swapped the 40010s from the working 6128 to the non working 464. Same result!

So hooray, the GA seems to be fine!

I swapped the Z80 with two known working Z80s. Same result.

I checked voltage on all (!) ICs, clean 5 Volts everywhere

I checked most of the traces for conductivity (data bus in particular); ok!

Symptoms so far:
- no basic command possible (syntax error)
- pressing "up" results in a "fat arrow"; I checked against the CPC character set, and it is NOT the same arrow as with ctrl+k or Shift+pound sign (see picture). All other keys seem to work ok (and it is not a fault of the kbd or menbrane, since I tried the 6128 kbd in the 464 with the same results)
- Dandanator related: I cannot start the RAM test (results in a "scambled" Dandanator screen) and I cannot start the "Uploader" (via "L") in the Dandanator (uploader shortly flashes, then it goes back to the Dandanator start screen)
Especially the Dandanator stuff is not easily explainable from a bad ROM ... any ideas would be greatly appreciated!

I think this is all I can do at the moment; the TL866II did not arrive yet. When possible, I try to borrow an oscillator from a friend, but he is currently indisposed.

- thomas

Offline Bryce

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My money is still on the Firmware/BASIC ROM having an issue.

Bryce.

Offline thomas

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Thank you Bryce! :-)
So I guess I have to test my patience and wait 'till the damn TL866 arrives ... man this is hard!

- thomas