Issue 3 Spectrum 48k no display no boot nothing
I picked up a untested Spectrum from ebay, hoping to relive some of my youth, I had a ZX81 back in the day and was always envious of my classmates when they got the speccy,
I would appreciate if you guys could help me bring it back to life
Before I turned it on I followed JoulesperCoulomb youtube video 'Initial Tests'
all tests seemed to be ok, transistors and diodes tested ok in circuit and resistances looked ok.
Im using a DC-DC converter set at 9v.
When I powered it up (around 450MA draw) there was no display. I went ahead and done the composite mod with capacitor, to rule out TV, same thing no display , the voltages at the DRAMS 4116 -5V +12V +5V are ok.
I changed all the capacitors and had a good look all over the board for damage or breaks and shorts, the board is actually in really good condition for its age, all good there.
So basically no video, no audio on key presses, I also shorted lines of KB1 and KB2 to test input.
Is there anything else to test before I start looking for ULA, Dram or CPU. I know the ULA is hard to get hold of, is it worth buying another spectrum just for the parts.
I bought a cheap USB 24MHz Logic Analyser, though I only used it once on an arduino so Im not used to it, would this help find my problem?
Is it worth testing all transistors out of circuit?
after 5 mins the VOLT REG, CPU, ULA, ROM and lower RAM gets a little warm around 30 degree, the upper ram stays bascically the same tho
Ive exhausted my ideas - any pointers where I should go next would be great thx