ZXPand firmware (paging SirMorris!)

[balford]

Hi,

Using my ZXPand yesterday evening, the current consumption shot up to over 2A (I use a voltage/current module in series with my PSU to monitor stuff like this). I immediately powered off, but long story short, the ZXPand now refuses to work (verified on another Zeddy to be sure it's not the system).

I have a Minipro TL866-CS programmer with which I've been able to verify that the two GAL IC's and the PIC seem intact and contain valid code, but the overlay EPROM is toast (returning FF FF for ID, and all FF's for its programmed image). I haven't attempted any SRAM verification as of yet though. I think the EPROM shorted its Vcc and Gnd rails temporarily causing the current spike.

The firmware seems to be working OK as the reset button produces the appropriate LED indications for short and long presses.

I tried reprogramming a 6.6 overlay image copied four times to a 32K image to a 27C256, but this didn't work.

So, my questions are:

1) Not having any 27C64's in stock, but one 28C64 - will this work as a substitute?
2) Where is the latest firmware repository for the ZXPand - I had overlay version 6.7 on the toasty EPROM.

Cheers,
B

[1024MAK]

Hmm, he normally posts updates in this thread, but I don't see 6.7 of the overlay ROM there

If you can't find a 27C64, I may have one.

With the larger EPROMs, I suggest you compare the pin-outs and then compare to the actual board connections.

What do you mean " I think the EPROM shorted its Vcc and Gnd rails temporarily causing the current spike"? Do you mean you think the EPROM failed internally, or the chip's pins were shorted out by some metalwork (Memotech case)?

Mark

[balford]

Thanks, I mention version 6.7 as that's what my EPROM was marked with

I have a 27C64 on order, but thanks for the offer I was just wondering if a 28C64 would work in its place as I see mention of it in early ZXPand development threads, but this may have changed with later board issues and I want to be careful.

I think the original EPROM suffered an internal failure, the board is held quite securely within the Memotech casing and there are no protruding legs that could short off anything.

B

[1024MAK]

Strange, CMOS chips don't normally go short circuit. Unless they experience an over voltage condition (supply or on an input pin). Then they can suffer latch-up. In a latch-up condition they do go short circuit and unless something external limits the current, they will be permanently damaged. See here.

I suggest you check your PSU

And check that no supply or ground tracks were damaged

I don't know off the top of my head if a flash or EEPROM can be used in place of the EPROM as I have not tried it. As far as I can see, only pin 27 is different, so if this is tied high to +5V, it looks like a 28C64 should work.

Mark

[balford]

Naturally the only 28C64 I have spare has a fault with its A0 address line

The PSU is good

Seems the SRAM is also bad, so ordered one of those too. The ZXPand is a purely digital board, so I'm fairly confident a new SRAM and EPROM will have it working again.

B

[PokeMon]

If a minor bit is missing this should result only in a minor failure.

[sirmorris]

Hello chaps. Long time no see!

I'm sorry to hear the board went incandescent. I'm glad there were no flames though

As you have a programmer I can send you an image of a 'memory only' GAL which you can test the RAM with, once you've removed the remaining chips from the board. If the machine boots and PEEK 16389 returns 128 you could save yourself some work and leave the RAM in place.

EEPROMs do indeed work. In fact, with a jumper and a new memory GAL program you can even program them in-place. Not particularly useful but quite novel.


C

[balford]

That would be great, cheers PM incoming...

B

[balford]

With Sirmorris' help, I've diagnosed the following:

- Dead EPROM
- Dead SRAM
- Dead I/O GAL

The PIC and the memory GAL are still good, however.

Replacements incoming, however the GAL's are coming from China which will slow the repair work up somewhat. I'll report back when I return to this, but in the meantime many thanks to all that helped

B

[tokabln]

Dear All,

I'm just having a problem with the ZXPand... the FW Version is 2.2 and the ROM Version is 6.0.
I'm actually not able to flash the latest ROM Version 6.6 and I'm not sure how to get this done...

Is there any specific command to get this done... btw. the board version is issue 1.0

Many thanks for some help

Regards tokabln