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General Category => Technical Support => Hardware related => Topic started by: thomas on 16:32, 15 February 21

Title: CPC 464 -- all basic commands result in Syntax Error & a pinched y
Post by: thomas on 16:32, 15 February 21
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
Title: Re: CPC 464 -- all basic commands result in Syntax Error & a pinched y
Post by: GUNHED on 21:06, 15 February 21
Looks like the lower ROM has problems / is corrupted. Should be easy to change (you can use an EPROM).
Title: Re: CPC 464 -- all basic commands result in Syntax Error & a pinched y
Post by: thomas on 21:41, 15 February 21
Thank you!

Just to make sure: the ROM is the 400007?
- thomas
Title: Re: CPC 464 -- all basic commands result in Syntax Error & a pinched y
Post by: Audronic on 00:09, 16 February 21
@thomas (https://www.cpcwiki.eu/forum/index.php?action=profile;u=4124)


No NOT the 40007


The ROM is 40009 (Left hand side )


Keep Safe


Ray
Title: Re: CPC 464 -- all basic commands result in Syntax Error & a pinched y
Post by: thomas on 09:12, 16 February 21
 :doh: ah yes -- I meant it! :-) The 40009 below the sond chip. Sorry!
- thomas
Title: Re: CPC 464 -- all basic commands result in Syntax Error & a pinched y
Post by: thomas on 21:11, 16 February 21
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
Title: Re: CPC 464 -- all basic commands result in Syntax Error & a pinched y
Post by: Gryzor on 10:23, 17 February 21
Will no one mention the black and white mode? :D
Title: Re: CPC 464 -- all basic commands result in Syntax Error & a pinched y
Post by: thomas on 13:59, 17 February 21
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
Title: Re: CPC 464 -- all basic commands result in Syntax Error & a pinched y
Post by: Bryce on 14:10, 17 February 21
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.
Title: Re: CPC 464 -- all basic commands result in Syntax Error & a pinched y
Post by: thomas on 14:24, 17 February 21
thank you Bryce! :-)
Title: Re: CPC 464 -- all basic commands result in Syntax Error & a pinched y
Post by: thomas on 10:12, 21 February 21
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! :-)

Title: Re: CPC 464 -- all basic commands result in Syntax Error & a pinched y
Post by: thomas on 10:16, 21 February 21
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
Title: Re: CPC 464 -- all basic commands result in Syntax Error & a pinched y
Post by: Animalgril987 on 14:40, 21 February 21
It wouldn't hurt to replace that cap, just in case.
Title: Re: CPC 464 -- all basic commands result in Syntax Error & a pinched y
Post by: thomas on 15:46, 27 February 21
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
Title: Re: CPC 464 -- all basic commands result in Syntax Error & a pinched y
Post by: Bryce on 16:36, 27 February 21
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.
Title: Re: CPC 464 -- all basic commands result in Syntax Error & a pinched y
Post by: thomas on 16:58, 27 February 21
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
Title: Re: CPC 464 -- all basic commands result in Syntax Error & a pinched y
Post by: thomas on 19:05, 28 February 21
small improvement: printed some cassette reset button replacements (available on thingiverse). They work quite nice!
Title: Re: CPC 464 -- all basic commands result in Syntax Error & a pinched y
Post by: thomas on 14:22, 04 March 21
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
Title: Re: CPC 464 -- all basic commands result in Syntax Error & a pinched y
Post by: Bryce on 15:29, 04 March 21
I'd suggest swapping the Z80 from the 6128 first to see if that's the issue.

Bryce.
Title: Re: CPC 464 -- all basic commands result in Syntax Error & a pinched y
Post by: thomas on 19:17, 05 March 21
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


Title: Re: CPC 464 -- all basic commands result in Syntax Error & a pinched y
Post by: thomas on 19:20, 05 March 21
ah, and bkspc pressed twice => beep! This is a good sign, I guess!
Title: Re: CPC 464 -- all basic commands result in Syntax Error & a pinched y
Post by: thomas on 19:30, 05 March 21
hm, ok "row 9" of the kbd matrix is connected to the AY. Maybe a fault there, but otherwise sound is working.
Title: Re: CPC 464 -- all basic commands result in Syntax Error & a pinched y
Post by: thomas on 15:54, 11 March 21
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
Title: Re: CPC 464 -- all basic commands result in Syntax Error & a pinched y
Post by: Bryce on 16:15, 11 March 21
My money is still on the Firmware/BASIC ROM having an issue.

Bryce.
Title: Re: CPC 464 -- all basic commands result in Syntax Error & a pinched y
Post by: thomas on 16:22, 11 March 21
Thank you Bryce! :-)
So I guess I have to test my patience and wait 'till the damn TL866 arrives ... man this is hard!

- thomas

Title: Re: CPC 464 -- all basic commands result in Syntax Error & a pinched y
Post by: Bryce on 16:27, 11 March 21
Thank you Bryce! :-)
So I guess I have to test my patience and wait 'till the damn TL866 arrives ... man this is hard!

- thomas

I could have sent you a programmed ROM. Where is the TL866 coming from?

Bryce.
Title: Re: CPC 464 -- all basic commands result in Syntax Error & a pinched y
Post by: thomas on 16:34, 11 March 21
China! :-(

Yes, that would be cool -- can I pm you?
- thomas
Title: Re: CPC 464 -- all basic commands result in Syntax Error & a pinched y
Post by: Bryce on 17:14, 11 March 21
China! :-(

Yes, that would be cool -- can I pm you?
- thomas

Sicher!

Bryce.
Title: Re: CPC 464 -- all basic commands result in Syntax Error & a pinched y
Post by: thomas on 17:19, 11 March 21
Großartig, Danke!
Title: Re: CPC 464 -- all basic commands result in Syntax Error & a pinched y
Post by: thomas on 13:39, 16 March 21
Hey! I got a new ROM today and it works! Most or all problems seem to be fixed (non working basic, pinched character, strange up arrow). On the way I fixed the int. speaker and printed me a new reset button. Yeah.

So thanks to all you guys for the help & patience, esp. Bryce.

- thomas


Title: Re: CPC 464 -- all basic commands result in Syntax Error & a pinched y
Post by: Bryce on 15:01, 16 March 21
Wow, that was fast, I only brought it to the post yesterday just after lunch! Glad it sorted the problem too.

Bryce.

Title: Re: CPC 464 -- all basic commands result in Syntax Error & a pinched y
Post by: thomas on 16:44, 16 March 21
yes, thank you again! I'm glad you sent me the ROM, because the ROM burner was anounced for Friday, then Saturday, then Monday and today "Hermes" told me, they f***ed it up and the package is lost. :-(
However, a CPC is resurrected. :-)
- thomas
Title: Re: CPC 464 -- all basic commands result in Syntax Error & a pinched y
Post by: thomas on 16:51, 16 March 21
before & after (the other way around of course) :-)