[Irinikus]

I received my package from the UK today, containing a dual ROM, new CPU and two new multiplexers!



First up, I slotted the new ROM chip and connected the machine up to my Indy, which gave me the following:



This indicates that all the lower RAM is bad! (And I've just replaced all the chips with brand new ones, so this is highly unlikely to be the true cause. It must be somewhere in the RAM interface or the CPU itself!)

I sent RETROLIUM a message, asking advice as to which component more than likely has failed and will need to be replaced and I'll take it from there. (I really think that it's unlikely that both multiplexers have failed, so in my mind it's more than likely a faulty CPU!)

At least the ULA seems to be ok, as I'm getting an image! (It, along with the "dead cockroach", really give this board character!)

[Irinikus]

Ok, I went ahead and swapped out the CPU and the multiplexers and still the same result!!!! (I really need a Weller Rework station, as this was painful! Desoldering the CPU and fitting the socket was easy, but the multiplexers were an absolute pain in the ass!!!)



I ended putting the original CPU in the socket, as the new CPU was giving me graphical artefacts.

Looking at the traces on the back of the board, the traces for the RAM bus all connect to the ULA!!!! (So this must be the defaulting component, as it must contain the memory controller!!!)

[Irinikus]

I'm still waiting for feedback from RETROLEUM, but it looks like I'll be needing one of these:

[Irinikus]

I did some more testing of this system today and found that the upper RAM is at least functional, this could possibly point to a power supply issue to the lower RAM!!!







So at least the upper RAM module is fine!



I've thought all along that the voltages supplied by the VRM on the board are all within limits, but I may be wrong! The Transistors seem to be fine (No internal shorts), but there may be an issue with some of the diode in the circuit!!!

The graphical output shows double in the vertical and double of every second letter in the horizontal! Non of the systems video RAM is operational at this point, but it is a strange output none the less!

---

I've just received the following response from Phil Ruston, who runs RETROLEUM:

Are the pictures that I’ve sent you consistent with a ULA failure?

Unfortunately, yes.

Regards,

--

Phil Ruston.


So unfortunately it appears to indeed be a ULA failure!!!!