Does anybody know anything about sinclair spectrums?

I bought a sinclair spectrum +2 and an amstrad cpc 464 on saturday for a fiver each, neither of them worked straight away but the amstrad just hasd a cracked DC jack and needed me to make an RGB cable so no problems there.
The spectrum however has been more troublesome. The RF box was knackered, the Dc jack was corroded beyond repair and the entire board was covered with some sort of gritty stuff. I've cleaned it up, got it powering on and attatched an RGB cable, so new problem.
This is the picture I get


Any suggestions? (My rgb wasn't fine, there was a dodgy connection because it's a cheap piece of junk)

 

If it's been abused I would suggest checking the motherboard for broken traces. There's also the possibility that the RAM is bad or the ULA is dead. If it's the latter you might as well find another Speccy, as working spare ULAs are hard to find from what I've heard.

 

Ok the doom and gloom is a position I've been considering but I'd like to try as much as possible before deciding that it is totally screwed
I took another, better video and replaced all of the capacitors
Also after the machine warms up, the picture changes a bit, I took a video but youtube is faffing about, I'll post it when I can.

Edit


After some research it looks like it's probably the ULA as you said apolloboy.
I'm disappointed but I refuse to give up
When I turn it on, the Zilog z80 CPU gets pretty warm which I'm guessing is normal, also the AY-3-8912A chip gets pretty warm
None of the ram chips get particularly hot and the ULA chip gets somewhat warm but nothing excessive, none of the other chips are noticeably warm and none of the traces aside from two I replaced as soon as I finished cleaning the board seem to be broken.
So, any chance at all it could be something a bit less horrible to replace like the transistors?

Also as I've had almost no help here, don't suppose anybody could point me towards a forum where someone might have some idea?

 

Never mind

 

You *could* ask at YakYak, the forum for Llamasoft Games which is full of old Speccy owners who might be able to help.

 

I'd try World of Spectrum as well.

 

I guess the only thing I can add to Apolloboy's advice is that I've come across dead Z80's on two 'as-is' Speccies I bought. I'll give you a rundown of how I initially try to pinpoint the deceased part.

With a DVM (some countries call it Multimeter), check the voltage between pins 11 and 29 of the Z80. If it's not 5V, there's a bad trace somewhere, or a shorted out part.
If the power's OK, check the voltage on pin 26 (reset line), if it's below 3V the Z80 is stuck in reset state.
Now what I do is to measure the voltage on pin 19 (/MREQ.) The 'scope is bulky and clumsy so I perform a quick check with the DVM first, it should be somewhere in the 2V-4V range (if it's 5V _or_ zero the Z80 is not running at all.)
And the last thing I'd do was to take out each DRAM IC and then run the machine to see whether the on-screen noise changed, if it did I'd replace that particular memory chip.

If all that failed, I'd write that ULA off as non-functional. There was this one bizarre ULA though, which if not-so-gently hit with a screwdriver would work for a few minutes... Freaky.

Anyway, hope this helps, and I hope it comes back to life!

*Edit* Oddly enough, one of my +2's began to behave like yours last night while I was following the procedure I described above, and it turned out to be IC17 (bit 0 of the lowest RAM bank) that died -- piggybacking a working DRAM chip on top of it brought the machine back to life. So I'd also try doing that to each individual DRAM IC on your +2, from IC17 to IC24.