Ok, I'll try connecting VCC to A15 on the 2.4 ROM and see what happens. It's difficult to tell with modern TV's what is going on, as you may have some messed up video output, but unless the TV recognises it as a valid format, it just says no signal. Not useful for debugging!!
Keep a old good CRT monitor for a service work
Philips CM8833 or a similar.
Yes, I have an oscilloscope and logic sniffer. I was wondering where to start... see if the Z80 bus is active?
- check the System Clock at U18 pin 12 (8MHz)
- check Z80 Clock at Z80 pin 6 (4MHz)
- check Video Clock at U37 pin 10 (14.237536 MHz)
- check Reset signal on Z80 pin 26 while pressing reset button. One impulse needed for each pressing.
- check 1MHz Clock at expansion bus pin A21
If no reset and no 1MHz then the Dave not running probably it is dead
For the video part check VCAS and VRAS on video RAM ICs (pin 15 and pin 4) and VMUX on U8,9 pin1. These are cyclic signals because the Nick always reading video memory. If no activity then Nick not running...
If these good then check RD, MREQ and M1 signal at Z80 (pin 21,19,27), if all do activity then CPU looks running. Then check ROM CE signal at EPROM pin 20. (I found few partialy dead Dave chips which are not generate ROM or CART signal, this is can be substitued by adding one address decoder IC)
