Spectrum 48k not booting to sinclair logo screen

[jonwarby]

I've been trying to repair a spectrum a friend has given me. I have tried to do as much as I can before asking for help but I dont seem to be making any progress. Does anyone have any suggestion as to what I can try next please.
Things done so far
This is more or less what I get when I turn it on. Sometimes white border or green.


Its an Issue 4B board
Very little difference if I boot with smart card V2 installed in diag mode.
I have another spectrum so I have swaped the ULA, socketed the CPU and swapped that and socketed the lower memory and replaced
voltages on the -5V +12V +5V are ok.

I have replaced all transistors and capacitors.

I have disabled upper memory and tested.... no change

Pin 14 on the ULA (IC1) gives 4.96V
Pins 14, 15 and 16 on IC14 (LM1889) gives 11.62V
Resistor R64 gives 4.96V

IC1 pin 13 for gives 3.6v

I have a voltmeter and a logic probe although still very new to this. If anyone does have a suggestion as to what to try next that would be really appreciated.

[MaxS]

Hello
if ULA & CPU are OK.. take a look at the ROM.

[jonwarby]

Thank you, will try that next.

[jonwarby]

I was hoping that the smart card would override the rom. I had assumed that was the same as taking the rom out and putting in a diagnostic rom.

This board the rom isnt socketed so will grab some time over the next few days and socket it.

[HappyLittleDiodes]

Any photos of the board and its chips?

Do the pixels move while it's on or is it frozen?

[jonwarby]

Most of the coloured pixels with patterns alternate between the two colours of the pixel. They dont move, just the colours invert.

Here is a picture of the board.

[jonwarby]

@MaxS thank you.... socketed the rom and tested from another machine and it booted to the logo. Will put it back together properly and do some more tests later.

As I mentioned earlier I had assumed the diagnostic card would bypass the rom so I had discounted that. Thank you for your help, really appreciated. I'm learning all the time.

[MaxS]

Lovely
Now carefully check the board. If the original ROM fried we must avoid it happens again.
Double check your soldering job.
Cheers
Max

[1024MAK]

The Z80 is not running. What does your logic probe show on the following pins:
Pin 6 (clock)
Pin 19 (MREQ)
Pin 25 (BUSRQ)
Pin 26 (RESET)
Pin 28 (RFSH)
?

Pin out details here

Mark

[1024MAK]

Most of the coloured pixels with patterns alternate between the two colours of the pixel. They dont move, just the colours invert.

That's the ULA flash working where the random data in RAM has the flash attribute bit set.

Here is a picture of the board.

WHAT has been done to that heatsink
It's not supposed to have a bend like that in it
I hope it was not bent while fitted to the board...

Mark

[jonwarby]

Everything seems to be running great now. Not sure what had killed the original Rom. All the transistors and capacitors I took off seemed to test fine. I have fitted the original lower memory back to the board and it's passing all the diag tests and playing games great.

WHAT has been done to that heatsink
It's not supposed to have a bend like that in it
I hope it was not bent while fitted to the board...

Mark

That was my solution to keeping the heatsink in place whilst working on the board. Not sure what other do. It's been bent back to original position now.