Harlequin rev g Spectrum clone black screen on boot

[Conrad Larsen]

Hi
I have built a Harlequin rev g Spectrum clone and get a black screen on boot. I have tried a few different roms also a diagnostic rom from from facebook Superfo Harlequin 128 page. I have checked the 5 volts and i am getting 5.77 volts on each chip. Not to sure where from here.

http://trastero.speccy.org/cosas/JL/Harlequin/Documentacion/harlequin_rev_g.pdf


Thanks
Conrad

[Ian.M]

A black screen + white border is normal for a speccy running its bootup memory test.  Its therefore starting to run but is crashing before it does anything useful.

5.77V is too high for the output of a LM2596-5.0, which shoud be in the range 4.8V to 5.2V.  It might be a good place to start. 

Otherwise its time for a wide logic analyser to trace execution and try to figure out if its crashing predictably.  Alternatively as this clone uses SRAM, you might be able to get somewhere with only a logic probe if you build a circuit to assert Z80 /WAIT after N M1 cycles, then allow you to single step the Z80, one M1 cycle at a time.