Spectrum Computing

quick update

I printed off the schematics and zoomed in on the CPU, ROM, PCF1306p area. I then worked through all of the connections between these chips (using the leg of the chips), all connections are fine on a cold board.

I'll run it for 20 mins or so and then do the same thing again..

Thanks both

I've ordered new sockets for the CPU and ROM, I'll replace both to firstly make sure there are no dry joints or other damage.

I'll then start working my way round the traces, starting with the CPU and ROM.

My multimeter has a continuity mode which should help

also, if thermal expansion is the culprit, am I correct in saying that I could check all the traces on a cold board and still not find any faults!

Makes sense Mark, I think it's clear at this stage that it's not the chips themselves, whilst it was up and running they all passed the diag rom tests.

It's going to be a slow process but I'll start working through the traces, fingers crossed I find something near the start of the process!

You're right Mark, I've just swapped the CPU into my 48k machine and left it running for an hour, all is well in that machine. I just find it really odd that all was well on the +2 for 10-15 mins after fitting the new CPU, then it started breaking down.. I hadn't moved it or touched anything, just l...

sorry, just another mini update I've just been testing some of the voltages on the chips 11 + 29 on the CPU = 4.9v 8 + 16 on the ram = 4.9v But.. when I initially tested the ram I tested the wrong pins, I used 8+9 and got a consistent 4.9v on the inner bank but only 4.14v on the bank closest to the ...

just another mini update on this.. New CPU arrived, I put it straight in the +2 and fired it up, diagnostic rom loaded fine, I was even able to go through all of tests, ram passed, ULA passed.. And just as I was getting my hopes up it started playing up, ten minutes after fitting the new CPU and it ...

Thanks Mark I'm experiencing similar symptoms to those you've described, one boot it'll beep and get as far as the menu, another boot I'll just get random colours on the border, if I then remove the rom and cpu to reseat them I might get it back to having the 8 beeps and maybe the "ram fail&quo...

Thanks Since posting the video the symptoms worsened, I'm not getting the initial beeps anymore, just a screeching sound and psychedelic bars on the border! I've ordered a brand new CPU just incase the one I'm using has been on its last legs. I've also ordered the ls04 chip you mentioned as these ar...

Thanks Mark I've just baked and ran the rom. Please see - https://we.tl/t-r9eqxeUZPp I did manage to get it to run once and actually say "ram fail" on the screen briefly, it looks like all of the ram is failing? but I can test both sets of ram in the Atari and it's fine on that and will ru...

Thanks both..

I've just had a go at making a 32kb testrom file as detailed by 1024mak

please see - https://we.tl/t-3TU0vB6VK6

Does this look correct?

got it..

one half matches the plus2-0.rom, the other half matches plus2-1.rom

so it looks like my ROM chip is ok..

I'll go ahead and burn the ZX-Diag .bin onto a chip and see if that provides any insights.

A friend of mine had this problem, it was a blown transistor, i'm not 100% sure which one off the top of my head but TR9 rings a bell.

If you've got a multimeter you can check the transistors yourself

quick update on this.. The programmer arrived today and I've saved a copy of the data on my rom chip. My plan was to compare this to a stock rom file to see if the data on mine looks corrupt but i'm confused, the dump of my rom is 32kb but all of the versions i'm finding on the web are only 16kb. As...

Thanks 1024MAK To answer your questions:- Equipment - I've got a multimeter but that's it at the moment The MB8264 chips are 150ns, they were removed from a working system, I could refit them in the Atari and run a memory test just to make sure they're ok. I've got both a temperature controlled sold...

Thanks for the comprehensive reply :D I've just ordered the EPROM programmer and a couple of blank chips, if nothing else I'll learn how to do something new :-) I've visually inspected the board but appreciate that this is far from scientific! It looks clean and tidy but I've read that they're not t...

Sadly I don't have a programmer, although I'd be tempted to pick one up if the process of writing a new rom is straightforward? it's something I've never done before..

Amazon sell a LAQIYA TL866Ⅱ programmer, is this what I'd need?

would you say that the behavior I'm seeing is typical of a bad rom?

Thanks

I've just tried that, no difference.. is it worth replacing the ROM socket?

Also, I don't have a spare rom and couldn't find them for sale?

Hi All Firstly, apologies for my first post involving me asking for help! I'm trying to resurrect my grey issue 3 +2 The first thing I did was order a new psu from the tfw8b, I also ordered an RGB scart lead. However, I'm struggling to get it to fire up :-( - please see attached image. Things I've t...