Author Topic: 464+ with no video  (Read 4373 times)

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Zup

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464+ with no video
« on: 10:50, 07 May 14 »
Hi

I've received a 464+ and I haven't had any of those before. The previous owner said that keyboard was faulty, but I can't check it yet. After connecting that to a PC PSU and a TV via SCART (without any battery), I had no video. The system cartridge (an ex-burnin rubber cartridge with a 27c1001 inside) was faulty, with a broken trace (it connected CCLR).

After repairing CCLR, the computer generates video (at least my TVs don't complaint about no video) but it only generates a black screen with black border. It has been tested on two TVs, and I can't hear anything from the 464+, it seems like it can't boot.

I've checked the cable, the power supply and there is no overheated chips on the board. Where can I start to find the failure?

On a side note, I built this cable but I have some doubts. Pin 8, 16 and 18 of the SCART are connected to the batteries, being pin 18 GND. Shouldn't it be also connected to other GND (e.g.: pin 4)? Also, I guess there is no point in using two batteries. How about using a +9v battery connected to pin 8 and 18 and a 330 or 330 ohm resistor between pins 8 an 16?

Thanks in advance.

Offline Bryce

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Re: 464+ with no video
« Reply #1 on: 14:02, 08 May 14 »
Hi Zup,
      The 464+ doesn't have an internal speaker, so you won't hear anything without connecting a speaker/headphone to the audio out port (on the left beside the joystick ports).

As for the 464+ generally, there's a good chance that the ASIC is dead, unfortunately not really repairable as you will only be able to get one of these from a working 464+, 6128+ or GX4000.

Regarding your side note: Noooooooooooooo!!!! Pin 16 needs a 1 - 3V signal to set the TV to RGB mode. How can you calculated the voltage drop accross the 330ohm resistor without knowing what's inside the TV behind pin 16?? On some TVs it may produce a 3V signal, but it would be just as possible that it only drops the voltage to 8V and you might instantly fry your TV!

Bryce.

Offline zup

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Re: 464+ with no video
« Reply #2 on: 14:51, 08 May 14 »
Sorry, maybe I didn't explain it well...

When I said that I had no sound, I meant that I couldn't hear nothing on the TV. I've also tried with headphones without success.

About the TV cable:

I supposed that there is a 75 ohm resistance between pin 16 and 18 (as I read somewhere), so I meant to do a voltage divider using the 330 ohm and the 75 ohm resistance to get about 1.6 volts on pin 16. If that's too risky, I'd try to:
- Connect pin 8 to +9v.
- Connect pin 18 to GND.
- Make a voltage divider with two resistors of 680 and 220 ohm (to get about 2.2volts) and connect it with a diode to get about 1.5 volts on pin 16.

It should look like this:

Code: [Select]
+9v ---+--------- Pin 8
       |
      680 ohm
       |
       +---|>|--- Pin 16
       |
      220 ohm
       |
GND ---+--------- Pin 18

That should give the required voltage without risk of damaging the TV, but the battery will slowly discharge even with the cable disconnected.

The cartridge I was given was faulty (no CCLR) and contained a System+ParaDOS EPROM. I've burned a diagnostic EPROM so I'll check it this evening, if it doesn't work my next task will be desoldering everything in the cartridge to check if there is another faulty trace. Also, I'm trying to get a known good cartridge, but it may take some time.

Also, I remember having the schematic for the cartridge, but I've lost and I can't find on the wiki. Does anyone have it?
« Last Edit: 17:35, 08 May 14 by zup »

Offline gerald

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Re: 464+ with no video
« Reply #3 on: 14:56, 08 May 14 »
Hi Zup,

What is your level of confidence on the cartridge itself. Did you had a chance to test it in another plus ? A dead cartridge EPROM can cause the symptoms your are describing.

Also, how was the cut done on CCLR track? Was there a sign of knife/cutter ?

Since you have access to a eprom burner, you should look at the cartridge eprom content as well. If it is OK (you can test it in an emulator or compare its content with a .CPR), ACID chip or ASIC a likely dead.

Offline Bryce

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Re: 464+ with no video
« Reply #4 on: 15:22, 08 May 14 »
I supposed that there is a 75 ohm resistance between pin 16 and 18 (as I read somewhere)

Only picture signals (ie: R, G, B, Composite, etc) are terminated with a 75R resistor. There is no standard or requirement for terminating resistors on any of the other pins, so you can't calculate the resistance as you have.

The cartridge pinout can be found here (from the layout PDF): DIY Cartridge - CPCWiki . You should be able to continuity test all signals to test the tracks without removing anything.

Bryce.


Offline zup

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Re: 464+ with no video
« Reply #5 on: 17:21, 08 May 14 »
I've tried my "new" cartridge and it almost work.

I have almost no conficence on that cartridge. The story behing it is that a coworker (the previous owner) tried to put in working order his 6128+, but got also his cousin 464+ (that has become my new toy). Soon he remembered that he needed a CP/M disk to format other floppies, so I burned a new EPROM (Spanish system + ParaDOS + Burnin' Rubber). He desoldered the old EPROM and put a socket and my new EPROM into the cartridge.

The cartridge returned to me because he thought that the EPROM was faulty, but both the EPROM and the original ROM are fine. I tested the pinouts and discovered that CCLR trace was damaged: it seems that he tried to pull up the original rom using a flat screwdriver and scratched the trace (that's the damage repaired).

I've made a diagnostic EPROM and when I started the computer, it showed black shadows over black screen. It seems that the 464+ is booting but the TV can't pick the signal. After some fiddling, I've heard the sound test so I guess the 464+ is booting.

I'm wondering if that system EPROM I made can boot correctly on a 464+ (because of lack of FDC), but before trying it again I need to do a working TV cable.

BTW, I'm going to convert it to a *128+ (128k, internal FDC, external floppy) but I couldn't get 41464 memories so I bought some TMS4464-10 chips. Can I mix up 41464-12 and TMS4464-10, or is it better to replace old memory and put 4 TMS4464-10 chips?

Offline Bryce

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Re: 464+ with no video
« Reply #6 on: 17:26, 08 May 14 »
I didn't think it was possible to have ParaDOS and Burning Rubber on the cartridge together, because ParaDOS uses some space that Burning Rubber start process also needs? Did you patch this EPROM file together yourself or is it a known working image?

But either way. If you own an EPROM burner, what other test equipment have you got and I (and others) could suggest some tested you could do.

Bryce.

Offline zup

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Re: 464+ with no video
« Reply #7 on: 17:39, 08 May 14 »
I used a downloaded image from CPC wiki, but after the tests with the diagnostic ROM I wonder if it can boot at all with a 464+ (on WinAPE it does, but there is no way to disable FDC emulation).

Now the 464+ seems to work, but the problem is rebuilding that TV cable to see the test results. Once I can peek at the screen, I'd try to get a working system cartridge and upgrade the computer.

BTW, my system is a spanish 464+ but I can't find the original ROM image. Does anybody know where can I get one?

Offline gerald

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Re: 464+ with no video
« Reply #8 on: 17:52, 08 May 14 »
I've made a diagnostic EPROM and when I started the computer, it showed black shadows over black screen. It seems that the 464+ is booting but the TV can't pick the signal. After some fiddling, I've heard the sound test so I guess the 464+ is booting.
That's a good news indeed  :)

I'm wondering if that system EPROM I made can boot correctly on a 464+ (because of lack of FDC), but before trying it again I need to do a working TV cable.
I am pretty sure 464+ and 6128+ use the same system cartridge.
Anyway, the way the FW start, you should at least see the copyright notice even before the AMSDOS/PARADOS get accessed and initialised.

BTW, I'm going to convert it to a *128+ (128k, internal FDC, external floppy) but I couldn't get 41464 memories so I bought some TMS4464-10 chips. Can I mix up 41464-12 and TMS4464-10, or is it better to replace old memory and put 4 TMS4464-10 chips?
These are compatible, you can mix them without problem.

Offline Bryce

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Re: 464+ with no video
« Reply #9 on: 17:55, 08 May 14 »
Gerald is correct, the 464+ and 6128+ cartridges are identical, the lack of FDC hardware wouldn't cause a problem. There are resistor/jumpers on the CPCs PCB to let the Firmware know how much RAM is present and whether an FDC is present.

Bryce. 
« Last Edit: 17:57, 08 May 14 by Bryce »

Offline zup

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Re: 464+ with no video
« Reply #10 on: 20:39, 08 May 14 »
Well, it seems that I've solved most problems.

I've managed to make a mostly working TV cable (some colours appear washed), but I can see what is happening on screen so it's fine for now.

It seems that the Spanish system + ParaDOS image on the cpcwiki don't boot on 464+. It gives a copyright message but then hangs, I guess that it must be related to R129 (that was factory installed on my computer) and the lack of FDC. Using the Arnold test ROM works.

The keyboard was faulty, it had f7 pressed and some other keys didn't work. After some cleaning, it works. The computer has passed the rest of the tests, so I think there is nothing broken inside it.

Now that it works (and I've got a RAM test), I'm going to upgrade it to 128k. When I got a new system cartridge (I'm out of EPROMs) and a SED9420, I'll try to install that floppy controller.

Thanks for your help.

Offline endangermice

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Re: 464+ with no video
« Reply #11 on: 20:40, 08 May 14 »
With regards to the power for pin 16, you could use a micro voltage regulator - you can get them fixed at 1.5v or variable. They're really small - around the size of a transistor and will ensure you don't destroy your TV. I've used these with good success in the past. Most smaller ones will only allow 150mA but I've yet to encounter a TV that has caused one of these to run hot or expire though in fairness, I've been going from a 5v source which is a significantly smaller drop than 9v so as always test this first before turning it into a permanent solution - they are available with higher current though tend to be rather larger. Unfortunately there seems to be no specification on how much current the blanking input (pin 16) will draw so again like the resistance this could vary across televisions. I would imagine the current draw to be minimal since this is just a control voltage but you never know..... I should probably measure it some day though of course it would be specific to my TV.....
« Last Edit: 20:45, 08 May 14 by endangermice »
For all the latest Starquake remake news check out my website - www.endangermice.co.uk

Offline Bryce

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Re: 464+ with no video
« Reply #12 on: 22:49, 08 May 14 »
Congrats on getting it back working. You probably already know exactly what you need to do for your upgrade, but if not, I've done a short guide here: 464Plus Conversion - CPCWiki

Bryce.

Offline redbox

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Re: 464+ with no video
« Reply #13 on: 22:57, 08 May 14 »
It seems that the Spanish system + ParaDOS image on the cpcwiki don't boot on 464+. It gives a copyright message but then hangs, I guess that it must be related to R129 (that was factory installed on my computer) and the lack of FDC. Using the Arnold test ROM works.

That's an interesting point about the 464+ cartridge because the 'Press f1/f2' code is contained in the AMSDOS ROM section of the 6128+ cartridge.  So does anyone know how the 464+ cartridge differs?

It is possible to patch the existing 6128+ cartridge without using ParaDOS to remove the 'f1/f2' message and this has the benefit that Burnin' Rubber is accessible by typing in ¦GAME etc.  You can find my patch here but my most recent one (v1.3 which also has support for 32 ROM board expansions like the MegaFlash) is only available for the English cartridge - if you want a Spanish version, let me know and I'll take a look for you.

Offline zup

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Re: 464+ with no video
« Reply #14 on: 20:28, 09 May 14 »
Ok, I've been spending some time upgrading to 128k, and I didn't get it to work.

I thought that the only components required for the upgrading were C12, C13, IC12, IC13 and R28. After some frustrating time, I've discovered that R55 was also needed (that I didn't bought and I don't have). Are this the only components involved with 128k upgrade or did I miss another one?

Offline Bryce

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Re: 464+ with no video
« Reply #15 on: 23:24, 09 May 14 »
So you didn't click on the link I mentioned: 464Plus Conversion - CPCWiki ?

Bryce.
« Last Edit: 23:26, 09 May 14 by Bryce »

Offline zup

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Re: 464+ with no video
« Reply #16 on: 16:47, 10 May 14 »
@Bryce: Sorry, I did print that article even before getting the 464+. But I read that too fast I failed to notice that sentence that stated what components were required to get the 128k expansion... so I went the hard way and checked the circuit diagrams (and failed to notice R55). I've got now every component except that nasty SED9420 (I bought it on internet, and it may appear in a week or two), so I'll put R55 when I got some time and the rest of components when the SED9420 comes.

(I haven't got a uPD765, but I guess that a 8272 will work)

@redbox: The cartridge is the same for 464+ and 6128+, but I'm not using the original system cartrige. I'm using the spanish + parados cartridge. I guess that cartridge boots directly into parados, and parados keeps waiting for a FDC that does not exist. This behaviour may not be (and I guess it is not) the same as the original system cartridge. The original system cartridge is expected to work in every computer in the plus range (maybe excluding the GX4000), so I guess it will bypass the AMSDOS ROM if no FDC is available.

Unfortunately, I'm out of available EPROMS (I've got no EPROM eraser). So until I manage to erase one of them, I'm stuck with the system + parados and the diagnostic EPROMS (enough to check the repairs done).

I've done some comparing between the french original system and the patched (1.0) one, so I've managed to do a 1.0 patched spanish ROM (I did it previously with the megaflash patch for 6128 OS). Fortunately, the system ROMs for different languages are similar, so it's easy to check those patches. Maybe I'll take a look to the rest of the patch to see if it can be "advanced" to your 1.3 version.

Offline redbox

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Re: 464+ with no video
« Reply #17 on: 19:17, 10 May 14 »
Good news - let me know if you get stuck and I'll dig out my notes.

Offline Bryce

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Re: 464+ with no video
« Reply #18 on: 22:05, 10 May 14 »
In case it doesn't work out, I have both the µPD765 and the SED9420 here (many of them) and I can send you some.

Bryce.

Offline zup

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Re: 464+ with no video
« Reply #19 on: 13:02, 11 May 14 »
I've finished to do some comparing between unpatched and patched versions.

The french version (v 1.0) actually implements the patch (5 bytes between 0x5e6 and 0x5ec). The english version (v 1.3) has the same patch and also changes the copyright version. No other changes are implemented on the cartridge version of the patched version.

In the megaflash version, I can see the "initialize" roms patch (bytes 0x2ed, 0x327, 0x337 and 0x48d).

So, I guess we can talk about three patches:
1.- Remove menu patch.
2.- Initialize 32 ROMs patch.
3.- Copyright message patch.

In the ROM version, only only patches 1 and 3 are implemented; in the megaflash version all three patches are implemented. Why don't delete ROM version and keep only "megaflash" version as standard? There are side effects on a CPC without megaflash when trying to initialize all ROMs?

EDIT: I've attached a file with spanish patched and unpatched system cartridges. The only spanish system cartridge included on CPCwiki is the "system + parados" one, so please anybody test and upload this. Thanks.

EDIT AGAIN: I'm going to do the french patched versions and "expand" more the spanish and english patched ones. Maybe tonight I'll attach another file.

ANOTHER EDIT: I've made patched versions of every system cartridge, they can be found some posts below (so I've deleted this post attached file).
« Last Edit: 23:20, 11 May 14 by zup »

Offline redbox

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Re: 464+ with no video
« Reply #20 on: 18:53, 11 May 14 »
Yes I think you are right about the patches and thanks for doing the Spanish version - good work :)

The reason for not just including the MegaFlash version is that it doesn't work in emulators - so I included the non-MegaFlash version for that reason.

Offline redbox

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Re: 464+ with no video
« Reply #21 on: 20:23, 11 May 14 »
Found my notes on the patches for the ROMs and thought it would be good to share here as I learnt a lot of this the hard way (as detailed below)...!

1. Remove Menu Choice Patch

The menu choice ('Press f1/f2') is actually in the AMSDOS 0.7 ROM (bank 3) of the Plus cartridge. However, we patch the routine in the OS ROM (bank 0) instead so that the AMSDOS ROM is unaltered and we can still start the Burnin' Rubber game using |GAME, |JEUX, |SPIEL or |JUEGO .

Code: [Select]
Original:

&05e5

       ld      de,&0679
       ld      hl,&c072
       ld      c,&07
       jr      &0621

Patch:

       ld      de,&0677         ; this is executed by execution address
       ld      hl,&0000         ; this will force MC START PROGRAM to start BASIC
       nop
       nop
       jr      &0621            ; MC START PROGRAM

2. Initialise 32 ROMs patch

At first I assumed just KL FIND COMMAND and KL ROM WALK needed to be patched but this resulted in an infinite boot loop in emulators and I gave up for a while. Then TotO and SyX produced Firmware 3.1 and used the same approach and I realised that this actually works on real hardware and the problem was with the emulators.

However, during thoroughly testing this patch on real hardware I found that during every 3-4 boots the system would hang.  I looked into this further and realised that the KL INIT BACK and RST 3 routines also needed to be patched and this resulted in v1.3 of my system cartridge and Firmware 3.12 .

Code: [Select]
&02ed - KL FIND COMMAND
&0327 - KL ROM WALK
&0337 - KL INIT BACK
&048d - RST 3

3. Copyright message patch

During boot, the OS ROM displays the text "Copyright" followed by control characters which move the cursor back by 9 spaces and overwrites this text with the Copyright symbol and 1985 Amstrad etc.  You can remove this bug by simply overwriting the Copyright text and control characters with the correct text.

Code: [Select]
&068b - Copyright message


Offline zup

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Re: 464+ with no video
« Reply #22 on: 23:29, 11 May 14 »
Ok, I've been busy patching every system cartridge.

I've made a 7z file containing every combination of patches for every language in .bin and .cpr formats. The variants are:

- Original non patched.
- Without menu (rb copyright).
- Megaflash ROM init, with menu (mf copyright)
- Megaflash ROM init without menu (rb+mf copyright).
- ParaDOS (parados copyright).
- ParaDOS with Megaflash ROM init (parados+mf copyright)

I can't check the megaflash variants, because WinAPE don't support 32 ROMs (but they DO boot). I guess they should work, but I can't be totally sure.
« Last Edit: 19:45, 13 May 14 by zup »

Offline CraigsBar

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Re: 464+ with no video
« Reply #23 on: 01:19, 12 May 14 »

I can't check the megaflash variants, because WinAPE don't support 32 ROMs (but they DO boot). I guess they should work, but I can't be totally sure.

Just as soon as I get the kit I have ordered (the stuff to complete my Bryce multi cart and a new EPROM programmer) I'll test this. I plan to make a 4 OS version is cart as follows.

Slot 00 - standard cart with parados
Slot 01 - the rb/mf patched
Slot 02 - firmware 3.12 and parados
Slot 03 - v3 classic ROMs

So will test it once I have it finished. Don't expect it soon however. The programmer is coming from China on free shipping

Offline Executioner

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Re: 464+ with no video
« Reply #24 on: 08:57, 12 May 14 »
I didn't think it was possible to have ParaDOS and Burning Rubber on the cartridge together, because ParaDOS uses some space that Burning Rubber start process also needs?

Actually, the Plus version of ParaDOS is supposed to be different and still include the |GAME, |JEUX commands so you can still play Burnin' Rubber.