JustCPC Mainboard: part list, shopping, solder technics, etc... Lets talk!

[Joseman]

Hi

Just received The Justcpc board and I think it's time for all to create a topic where we talk how to build our new CPC!!

I haven't too much time... but i really want to start this!! 

First a pic of mine:

[fatbob]

I have mine and most of the parts but am waiting to find out what u28 is and where to find the firmware for it. The firmware for u55 also needs to be made available.

[fatbob]

I have a suspicion that U28 is a ATtiny2313 and the firmware is from here and the GAL at U55 wight have the code from here but I would like to at least be sure about  U28 before I start assembling.

[Joseman]

I have a suspicion that U28 is a ATtiny2313 and the firmware is from here and the GAL at U55 wight have the code from here but I would like to at least be sure about  U28 before I start assembling.

You're right This is from a message of Piotr:

"ATTINY2313 (U28) for keyboard controller"

[Joseman]

Here are the sockets that i will use for the mainboard, they are recommended by @Bryce, and they are high quality!!



GS 14P: IC-Sockel, 14-polig, superflach, gedreht, vergold. bei reichelt

GS 14P | GES-ELECTRONICS

[Joseman]

Hi again

I'm doing a parts list and i see that the U44 flash memory at27c256, if i understand correctly, is the sustitute of the AMSDOS ROM, but the pinout is not exactly the same...

my doubt: is the socket U44 compatible with the original AMSDOS 40015 ROM, or do we have to use only the atmel AT27C256?

[skywalky]

I think not because the 40015 can be substituted by an EPROM and the AT27C256 is an EEPROM.

[gerald]

I think not because the 40015 can be substituted by an EPROM and the AT27C256 is an EEPROM.

AT27C256 is a 32kx8 EPROM, where did you read it is an EEPROM/flash ?

[skywalky]

AT27C256 is a 32kx8 EPROM, where did you read it is an EEPROM/flash ?

Sorry, I thought that the Atmel was a Flash. 

[Joseman]

But the pinout is relatively similar...

is possible to use the 40015 instead?

[gerald]

Sorry, I thought that the Atmel was a Flash. 

ATMEL is the manufacturer 
27Cxxx is an industry srandard and are all EPROM

[gerald]

But the pinout is relatively similar...

is possible to use the 40015 instead?

I do not see why you couldn't 
Pinout is identical, except VPP wich is not present on the 40015.
VPP provides the high voltage needed to program the eprom. During normal operation and should be tied to VCC.

[amstar]

Very nice board! But this board needs an enclosure. Something like the Just Speccy inside real Spectrum ZX case would have been great. But I guess that is probably unlikely.
Looks like Zaxon in one of his videos has put it inside a standard desktop PC case (
JUST CPC, my clone of Amstrad CPC, final - YouTube ).
Would the board fit inside a standard ATX or mini-itx case ? 

[Bryce]

Hi,
    just started my Christmas break and decided to start building the JustCPC, mainly using parts from an original 6128 with a destroyed PCB. I'll make comments as I go along, so here's the first:

There are two rows of resistors, one below the reset switch (R37, R31.... R40) and another in the centre of the PCB (R30, R29.... R23). These have been so tighly packed together that standard 1/4W resistors don't stand a chance of fitting, in fact even 1/8W resistors have a hard time fitting here. This also means that the solder pads are extremely close together so there's a high risk of causing a short between pads for those who haven't a lot of soldering experience. 1/8W resistors are hard to find these days, you should consider spacing these a bit more generously on the next layout revision. Also, the component names on the PCB silkscreen are offset, so many of the names are covered by a previously installed component, so the user needs to refer to the online silkscreen picture which strangely has been done properly.

The distance (length) between resistor pins is 7.5mm, which is the absolute minimum for 1/4W resistors, so the pins need to be bent sharply directly at the component. This isn't great, the distance should really be at least 10mm for a proper fit.

Some resistors have been placed under ICs such as R18/R19 under U9, which isn't a problem as such, however, expensive round pin IC sockets have a support bar at these exact positions, so if you use good sockets, you'll need to remove the supports first.

Bryce.

[Bryce]

So the last bits I was missing arrived this morning and I had a chance to finish the board. Many of the parts, from the crystal, ICs, transistors and even a few resistors and capacitors were donated from an original 6128 that was sadly unrepairable. I have only tested the power circuitry (which I have beefed up slightly above the original design) so far, but I'll give it a full test next year (tomorrow ). It's completely socketed with the more expensive turned-pin sockets, so debugging will be pretty easy. Here's the finished board.

Bryce.

P.s. Any one got an idea what J6 and J7 do?

[Bryce]

@Piotr: Can you tell me what pin 1 of IC U10 is connected to? I've powered up the board and it boots to a white screen with black border (not a RAM problem, I have known good RAM ICs). I've probed a bit with the scope and I'm getting some extremely suspect signals.

Also:
- I'd still like to know what J6 and J7 do?
- Have you repurposed the spare gates on the 74LS08 in the FDC, because removing this IC stops the CPC from booting at all, but it wouldn't do that on a real CPC6128?
- What are unused inputs tied to? 5V or GND?
- The Mini-DIN Sockets have footprints for shielding, but the shields are floating, not grounded!!

Bryce.

[Bryce]

@Piotr:

First off, can you please start supporting your product by at least answering buyers questions (see above, plus the PMs I've sent you).
Secondly, has this PCB actually been tested as working? because I'm starting to believe that the PCB has errors. I am using all known good ICs and it still only boots to a white screen with black border. Please tell me you are not selling untested/confirmed PCBs.
Thirdly, can you please release the schematics you've used, because debugging is extremely difficult as you re-assigned all the component names making the original Amstrad schematic pretty useless.

Thanks,
Bryce.

[arnoldemu]

@Piotr:

First off, can you please start supporting your product by at least answering buyers questions (see above, plus the PMs I've sent you).
Secondly, has this PCB actually been tested as working? because I'm starting to believe that the PCB has errors. I am using all known good ICs and it still only boots to a white screen with black border. Pleas tell me you are not selling untested/confirmed PCBs.
Thirdly, can you please release the schematics you've used, because debugging is extremely difficult as you re-assigned all the component names making the original Amstrad schematic pretty useless.

Thanks,
Bryce.

He may still be on holiday and took a break from wiki and forum?

[Bryce]

Possibly, but that still doesn't excuse the lack of documentation. I recently built Pokemons "ZX80Core" and it comes with extensive documentation of the hardware.

Bryce.

[Bryce]

Nope, he has been online several times since I sent the PMs and hasn't answered them or the queries in this thread.

Bryce.

[Gryzor]

Don't forget email notifications are not working yet on the new server...

[TotO]

When you are online, the new message notification work (icon and popup).

[Bryce]

When you are online, the new message notification work (icon and popup).

Exactly, and he has been online.

Bryce.

[TFM]

When you are online, the new message notification work (icon and popup).

Confirmed!

[Bryce]

Looks like @Piotr is sneaking on here, but ignoring all questions about his hardware. Great support Piotr, way to go!

Bryce.