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General Category => Amstrad CPC hardware => Topic started by: protek on 09:55, 11 December 12

Title: Changing CRTC
Post by: protek 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.
Title: Re: Changing CRTC
Post by: TotO 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/ (http://cpcparts.net/)
But, they look to be no more listed... Better to send an email to ask.
Title: Re: Changing CRTC
Post by: protek 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.
Title: Re: Changing CRTC
Post by: fgbrain 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  :'(
Title: Re: Changing CRTC
Post by: Bryce 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.
Title: Re: Changing CRTC
Post by: protek 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.
Title: Re: Changing CRTC
Post by: Bryce 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.
Title: Re: Changing CRTC
Post by: protek 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.
Title: Re: Changing CRTC
Post by: Bryce 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.
Title: Re: Changing CRTC
Post by: ralferoo 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'.
Title: Re: Changing CRTC
Post by: Bryce 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.
Title: Re: Changing CRTC
Post by: gerald 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  ;)
Title: Re: Changing CRTC
Post by: Bryce 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.
Title: Re: Changing CRTC
Post by: protek 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.
Title: Re: Changing CRTC
Post by: db6128 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.
Title: Re: Changing CRTC
Post by: protek 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.

(http://dl.dropbox.com/u/25300140/WP_000116.jpg)
Here's our unsuspecting CPC.

(http://dl.dropbox.com/u/25300140/WP_000117.jpg)
And after a few screws the top lid is off.

(http://dl.dropbox.com/u/25300140/WP_000119.jpg)
Here's a close-up of the chip we're going to change.

(http://dl.dropbox.com/u/25300140/WP_000120.jpg)
To get the motherboard off, we need to unplug all the cables and remove the disk drive. The Amstrad is surprisingly easy to dismantle.

(http://dl.dropbox.com/u/25300140/WP_000121.jpg)
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.

(http://dl.dropbox.com/u/25300140/WP_000122.jpg)
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.

(http://dl.dropbox.com/u/25300140/WP_000124.jpg)
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...
Title: Re: Changing CRTC
Post by: Bryce on 11:03, 07 January 13
Looking good so far.

Bryce.
Title: Re: Changing CRTC
Post by: db6128 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!
Title: Re: Changing CRTC
Post by: protek on 16:47, 07 January 13
Today I cleaned rest of the connections and then soldered the socket in place.
(http://dl.dropbox.com/u/25300140/WP_000125.jpg) (http://dl.dropbox.com/u/25300140/WP_000125.jpg)

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.
(http://dl.dropbox.com/u/25300140/WP_000126.jpg) (http://dl.dropbox.com/u/25300140/WP_000126.jpg)

Looking good. :)
(http://dl.dropbox.com/u/25300140/WP_000127.jpg) (http://dl.dropbox.com/u/25300140/WP_000127.jpg)

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.
(http://dl.dropbox.com/u/25300140/WP_000129.jpg) (http://dl.dropbox.com/u/25300140/WP_000129.jpg)
Title: Re: Changing CRTC
Post by: Marq 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.
Title: Re: Changing CRTC
Post by: protek 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 (http://www.ebay.com/itm/120922013185)
Title: Re: Changing CRTC
Post by: steve on 21:40, 07 January 13
I have read on other forums of people receiving fake chips from utsource.
Title: Re: Changing CRTC
Post by: Bryce 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.
Title: Re: Changing CRTC
Post by: protek 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?
Title: Re: Changing CRTC
Post by: steve 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.
Title: Re: Changing CRTC
Post by: protek on 22:04, 07 January 13
Yup, I've ordered some memory before for my RTG card and those worked.
Title: Re: Changing CRTC
Post by: Bryce on 22:08, 07 January 13
I'd certainly order there again and probably will in the near future. I've just checked my orders and I've tonnes of stuff from them:

AD724
µP765
SED9420
FDC9266
27C160
27V160
WDC1770
WDC1772

And a few hundred 74LSxx ICs as well. Not a single fake among them. If you are ordering big numbers of parts I'd recommend doing it from their site and getting a quote, rather than ordering through ebay.

Bryce.
Title: Re: Changing CRTC
Post by: TFM on 22:15, 07 January 13
Just out of curiosity: Would it be possible to solder different CRTCs over each other and only activate the Chip-select signal of one of them. So a switch could select one of them. Or do I miss something?
 
Title: Re: Changing CRTC
Post by: Bryce on 22:28, 07 January 13
No. As mentioned earlier (can't remember who, it wasn't me :( ), the CRTC is always outputting a signal and reading RAM, the CE is actually a CS, so it only enables / disables the address input lines, not the entire IC.

Bryce.
Title: Re: Changing CRTC
Post by: protek on 22:32, 07 January 13
Bryce, do you remember what kind of delivery times Utsource has had? Mine was shipped yesterday from Hong Kong. I did the transaction already before Christmas, though.
Title: Re: Changing CRTC
Post by: Bryce on 22:40, 07 January 13
Around Christmas is never going to be a good time. I think most of my stuff arrived between 15 to 30 days from the order date.

Bryce.
Title: Re: Changing CRTC
Post by: TFM on 22:46, 07 January 13
No. As mentioned earlier (can't remember who, it wasn't me :( ), the CRTC is always outputting a signal and reading RAM, the CE is actually a CS, so it only enables / disables the address input lines, not the entire IC.

Bryce.
May be there any other pin usable? Vpp?
Title: Re: Changing CRTC
Post by: Bryce on 22:55, 07 January 13
Maybe, you'd need to test it. You also couldn't put many in parallel, the analogue outputs will all have resistors to ground, so each extra CRTC effects the image a little, even if it's not powered.

Bryce.
Title: Re: Changing CRTC
Post by: TFM on 22:58, 07 January 13
Ok, so back to the text tool socket.
Title: Re: Changing CRTC
Post by: Bryce on 23:02, 07 January 13
Would a ZIF Socket fit in there? They are pretty high, would it not hit the keyboard?

Bryce.
Title: Re: Changing CRTC
Post by: TFM on 23:05, 07 January 13
Good question, rather not. But I haven't been completely serious.  ;)  The best way is probably to just switch the keyboard instead of the CRTC. Ok, so you need at least three CPC6128 keyboards.  :laugh:
Title: Re: Changing CRTC
Post by: db6128 on 00:47, 08 January 13
I’ll stick with a normal socket and just use a screwdriver if I need to. :P
Title: Re: Changing CRTC
Post by: TFM on 04:03, 08 January 13
That could be more often the case when watching demos...
Title: Re: Changing CRTC
Post by: protek on 08:55, 15 January 13
Just received notification that the new CRTC had arrived in Oulu. Stay tuned....  ;)
Title: Re: Changing CRTC
Post by: protek on 23:07, 15 January 13
Received the new CRTC chip today from UtSoucre. It is a HD6845SP, which is type 0, if I remember correctly.
(http://dl.dropbox.com/u/25300140/WP_000135.jpg)

Since I had the socket already in place, it was a simply a matter of plugging the new chip in and we were set.
(http://dl.dropbox.com/u/25300140/WP_000136.jpg)

(http://dl.dropbox.com/u/25300140/WP_000137.jpg)
Phew! Safely in Locomotive Basic! :D

Now the moment of truth. Are we able to run the Batman Forever demo, which wouldn't run on the original type 2 CRTC?

(http://dl.dropbox.com/u/25300140/WP_000138.jpg)
So far so good...

And here we go! :D
(http://dl.dropbox.com/u/25300140/WP_000139.jpg)

(http://dl.dropbox.com/u/25300140/WP_000140.jpg)

Was it worth the trouble? Definitely. I've been hoping to see Batman Forever demo on real hw for some time.

If someone has the type 2 by Motorola in their Amstrad and wishes to upgrade, UtSource has the type 0 by Hitachi for sale at eBay.
Title: Re: Changing CRTC
Post by: db6128 on 23:41, 15 January 13
Good to know that the SP works just as well as the S, which is the one quoted in all the tables online.
 
I bought a type 1 (UM6845R) and have a type 0 (UM6845) in my ailing 464, so I will replace the type 2 in my 6128 eventually. But the socket I ordered hasn’t arrived. :|
Title: Re: Changing CRTC
Post by: TFM on 22:57, 16 January 13
Patience is a virtue  ;)   Code a 16 KB ROM game meanwhile  ;)
Title: Re: Changing CRTC
Post by: Syncmaster319 on 01:03, 09 March 19
Hi all,

Sorry to resurrect this old thread but search brought me here and wondered if the advice was any different.

I have a newly acquired near mint 6128 which was an eBay impulse purchase.  No regrets!

Unfortunately it has a CRTC 2 so a lot of the good demos don't run.  Is it still the case I can swap the CRTC out? 

If so which CRTC would you recommend and where can I purchase both a socket and a compatible chip?

Thanks in advance!
Mark
Title: Re: Changing CRTC
Post by: TotO on 01:30, 09 March 19
May be someone programming demo will enjoy to exchange a mainboard for your CRTC2 version instead?
Else, I should provide you a socket and a CRTC 1 if you want the good one to run most demos.



Hi all,

Sorry to resurrect this old thread but search brought me here and wondered if the advice was any different.

I have a newly acquired near mint 6128 which was an eBay impulse purchase.  No regrets!

Unfortunately it has a CRTC 2 so a lot of the good demos don't run.  Is it still the case I can swap the CRTC out? 

If so which CRTC would you recommend and where can I purchase both a socket and a compatible chip?

Thanks in advance!
Mark