Author Topic: Changing CRTC  (Read 6057 times)

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Offline protek

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Changing CRTC
« on: 09:55, 11 December 12 »
Has anyone changed their CRTC to a different type? Mine's a type 2, which seems to be incompatible at least with the Batman demo.

Is there any downsides, if I change from type 2 to another and what type should I change it to? I have a CPC6128.

Online TotO

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Re: Changing CRTC
« Reply #1 on: 10:25, 11 December 12 »
No, you can change it to put a Type 1 or a Type 0 w/o problem.

Previously you can get them for free (no abuse) at : http://cpcparts.net/
But, they look to be no more listed... Better to send an email to ask.
"You make one mistake in your life and the internet will never let you live it down" (Keith Goodyer)

Offline protek

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Re: Changing CRTC
« Reply #2 on: 22:55, 19 December 12 »
I found a Hitachi one from ebay. Type 0 I believe. I'm going to get a socket and desolder the old one an put the new one in the socket.

Offline fgbrain

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Re: Changing CRTC
« Reply #3 on: 23:07, 19 December 12 »
Quote
Has anyone changed their CRTC to a different type? Mine's a type 2, which seems to be incompatible at least with the Batman demo.

I have changed my CRTC from type 2 to type 0 and used an IC socket to install it. Type 2 is the worst crtc to have. Besides most advanced demos, I could not play Zaptballs game with type 2..

Back in the 90s I heard that NWC had installed all three crtc types and used a switch for selecting between them.

Bryce once told me that he will upload a guide for such a mod... Still nothing  :'(
_____

6128 (UK keyboard, Crtc type 0/2), 6128+ (UK keyboard), 3.5" and 5.25" drives, Reset switch and Digiblaster (selfmade), Inicron Romram box, Bryce Megaflash, SVideo & PS/2 mouse, , Magnum Lightgun, X-MEM, X4 Board, C4CPC, Multiface2 X4, RTC X4 and Gotek USB Floppy emulator.

Offline Bryce

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Re: Changing CRTC
« Reply #4 on: 23:10, 19 December 12 »
I can't remember promising that? :D But whatever, I can do it if you like, I'll check it out over the Christmas break.

Bryce.

Offline protek

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Re: Changing CRTC
« Reply #5 on: 11:10, 20 December 12 »
Any point in saving the type 2 CRCT or should I do it the easy way and snip the IC legs and then desolder each leg?

The latter is exactly what I'm planning to do, when I change the bad DMA chip from my STE.

Offline Bryce

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Re: Changing CRTC
« Reply #6 on: 11:56, 20 December 12 »
Ok, just had a quick look. If you intend connecting several CRTCs to a CPC, then you need to connect all pins in parallel except for pin 25 (/CS), then use a switch to connect pin 25 of the CRTC you want to use. Each pin 25 should have it's own weak pull-up resistor to ensure that the IC really is turned off, ie: connect each pin 25 to the 5V rail via a 10K resistor. See badly drawn schematic below...

Bryce.

Offline protek

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Re: Changing CRTC
« Reply #7 on: 14:04, 20 December 12 »
Thanks for the schematic, Bryce!

I see a possibility to a PCB here, a bit like the Amiga's Kick ROM switchers.

Does the 5V for the resistors have to be pulled from the motherboard or can it be pulled from the VCC pin of the CRTC? I'd suspect it to have at least one such pin.

Offline Bryce

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Re: Changing CRTC
« Reply #8 on: 16:16, 20 December 12 »
The 5V on the CPC and the Vcc pin of the CRTC should be the same thing! But obviously the Vcc pin is nearer and easier to use.

Yes, It's almost identical to a Kickstart Switcher, just a different pin is used to select the chosen IC.

Bryce.

Offline ralferoo

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Re: Changing CRTC
« Reply #9 on: 21:43, 31 December 12 »
I'd be wary of doing this mutliple CRTC mod unless someone has actually confirmed it works.

Pins 4-19 and 34-40 are all output, so you should really multiplex them. As far as I know, CS' is only used in combination with R/W' and E to decide whether the CPU is selecting the device and so enables D0-D7. MA/RA/DE/HS/VS/CURSOR would normally be driven all the time regardless of CS'.

Offline Bryce

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Re: Changing CRTC
« Reply #10 on: 03:01, 01 January 13 »
No,CS should disable all inputs and outputs if it's done properly. Most ICs are completely shut down when CS / CE is high. If it wasn't, it would be documented as a known bug.

Brace.

Offline gerald

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Re: Changing CRTC
« Reply #11 on: 15:41, 01 January 13 »
No,CS should disable all inputs and outputs if it's done properly. Most ICs are completely shut down when CS / CE is high.
Usually, CS/CE is an input that that tells a device that it should care about other signals associated to this CE/CS (ie a bus). On a memory device, you may consider that the while device is not accessed, IO are not driving and input are ignored. BUT this is only one class of device.

On CRTC, CS/CE is related to register access only, CRTC generated signals (addr/hsync/vsync) are always active.

If it wasn't, it would be documented as a known bug.
If it was, the CPC would display something only when address bit 14 is low  ;)

Offline Bryce

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Re: Changing CRTC
« Reply #12 on: 17:41, 01 January 13 »
Doh, Yeah, you're right, I hadn't thought of that. The CRTC is practically always on :( Then my circuit above doesn't work, you'll have to put the select switch on the 5V rail and the resistors obviously won't be needed any more.

Bryce.
« Last Edit: 17:43, 01 January 13 by Bryce »

Offline protek

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Re: Changing CRTC
« Reply #13 on: 18:15, 02 January 13 »
I suppose I'm going to take the easy approach and simply snip the old CRTC off, de-solder the legs and put the new one in a socket in its place.
Luckily I've had practice as I just changed the DMA chip in my Atari STE. It is also a 40-pin DIL chip.

Offline db6128

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Re: Changing CRTC
« Reply #14 on: 22:45, 03 January 13 »
I suppose I'm going to take the easy approach and simply snip the old CRTC off, de-solder the legs and put the new one in a socket in its place.
I received a type 1 CRTC (UM6845R) today that I might eventually use to replace the type 2 in my 6128 (or alternatively use the type 0 out of my ailing 464), if I end up deciding that using real hardware is worth the effort…and if so, I think I will use a socket, too, because (A) it’s hypothetically possible that I would want/need to swap between the 0 and 1 at some point, and (B) there’s no good reason not to install a socket if the hardware allows it, IMO.
[The owner of one of the few existing cartridges of Chase HQ 2] mentioned to me that unless someone could find a way to guarantee the code wouldn't be duplicated to anyone else, he wouldn't be interested.
Did he also say things like "My treasureeeeee" and is he a little grey guy?

Offline protek

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Re: Changing CRTC
« Reply #15 on: 07:35, 07 January 13 »
So, I decided to change a new CRTC. I found a type 0 from the ebay and I'm expecting it to arrive in a couple of weeks so in the meantime I'll snip the old chip off and put in a socket for the new one.


Here's our unsuspecting CPC.


And after a few screws the top lid is off.


Here's a close-up of the chip we're going to change.


To get the motherboard off, we need to unplug all the cables and remove the disk drive. The Amstrad is surprisingly easy to dismantle.


If there's no need to save the old IC, it is easiest just to cut the legs so that you can desolder each leg separately.


Here we have the old legs removed. I applied some fresh solder to each pin to make the joint easier to melt. I had the motherboard upside down over the edge of the table and very gently pulled the pins down while applying heat with the iron from the top.


Then it was a matter of cleaning the holes of the remaining solder. Again I applied heat from the one side and used a desolder pump on the other. Here we have one row cleaned up.

It was getting late (or early) so I decided to leave the cleaning of the other row and soldering of the socket to another day. :tired:

To be continued...

Offline Bryce

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Re: Changing CRTC
« Reply #16 on: 11:03, 07 January 13 »
Looking good so far.

Bryce.

Offline db6128

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Re: Changing CRTC
« Reply #17 on: 15:20, 07 January 13 »
If there's no need to save the old IC, it is easiest just to cut the legs so that you can desolder each leg separately.
‘OMG! How can you even speak about throwing away a classic vintage ch… Oh, wait, it’s a type 2 — where’s my hammer?’ :D

Nice guide so far. I’m thinking about doing something very similar – installing a socket in my 6128 to replace its current type 2 and making it ‘switchable’ (i.e. open and replace) between a type 1 from eBay and the type 0 from my 464 (which will receive the type 2 if I ever decide to use/sell it) – so I’ve been watching this thread with interest and will be paying special attention from now on!
[The owner of one of the few existing cartridges of Chase HQ 2] mentioned to me that unless someone could find a way to guarantee the code wouldn't be duplicated to anyone else, he wouldn't be interested.
Did he also say things like "My treasureeeeee" and is he a little grey guy?

Offline protek

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Re: Changing CRTC
« Reply #18 on: 16:47, 07 January 13 »
Today I cleaned rest of the connections and then soldered the socket in place.


Having learned from my experiences with the Atari STE DMA chip change, I double checked the joints with a magnifying glass and re-applied solder, where needed.


Looking good. :)


Then it was a matter of putting the motherboard back. I left the top lid unscrewed as I don't yet have the replacement CRTC. It should be on its way from Utsource. Hopefully I'll receive it within a next few weeks.
« Last Edit: 16:51, 07 January 13 by protek »

Offline Marq

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Re: Changing CRTC
« Reply #19 on: 18:34, 07 January 13 »
Just out of curiosity: Where did you source that CRTC? Haven't seen them for sale anywhere, except the trashy Motorola one.

Offline protek

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Re: Changing CRTC
« Reply #20 on: 21:25, 07 January 13 »
Just out of curiosity: Where did you source that CRTC? Haven't seen them for sale anywhere, except the trashy Motorola one.
It was from Utsource via ebay. Here's a direct link: HD6845SP Manu Hitachi Encapsulation DIP 40 as Series Tandem Switch Single | eBay

Offline steve

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Re: Changing CRTC
« Reply #21 on: 21:40, 07 January 13 »
I have read on other forums of people receiving fake chips from utsource.

Offline Bryce

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Re: Changing CRTC
« Reply #22 on: 21:50, 07 January 13 »
I've bought quite a bit of stuff from UTSource. The AD724s for my S-Video adapters came from them, so did quite a few EPROMs and other stuff. I've never had a single problem. All their stuff was top quality and well packed.

Bryce.

Offline protek

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Re: Changing CRTC
« Reply #23 on: 21:52, 07 January 13 »
I have read on other forums of people receiving fake chips from utsource.

Fake as in counterfeit or fake as in being something totally different than it claims to be?

Offline steve

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Re: Changing CRTC
« Reply #24 on: 21:59, 07 January 13 »
Fake as in not being what they claim to be.

However Bryce has had good results from them so maybe it is nothing to worry about.