MP1 wont work with either 2.0 or 2.01 EPROM

[rnolan]

So here's a weird one.  My tech has been working on one of my MP1s trying to get it to work properly. It has the power up problem where you have to switch it on/off a couple of times before it boots. Once its warmed up it seems fine. It's a 1.38 EPROM
So as I have another MP1 (US model with 2.01 EPROM) we swapped the Z80 CPU, RAM chip and EPROMs (one at a time) to see if that helped. It made no difference except that when we put in either the 2.0 EPROM (from Mikes MP1, he now has 2.01) or the 2.01 EPROM from the US model (which works fine) we just get the program number flashing.  When we put back the 1.38 EPROM it works.  The 1.38 EPROM has no sticker on it and the erase window on the top of it is exposed.  So I'm wondering if the unit has been modded and the firmware (EPROM) changed to suit  .  I've never had an issue in the past going to either 2.0 or 2.01 EPROMs.Both units are older top switch models.  The problem unit is a Rev e mother board and the US model Rev f and there are some differences around the power supply diodes.

[MarshallJMP]

Tell your tech to change C136 with a 470nF cap and see if that helps with the startup problem.

I only had this once that when I changed the eprom to a higher version it didn't work. What you could try is to erase the RAM first and then try the 2.01. Not sure if it will do anything?

Can you email me a pic of your board?

[rnolan]

Hey MJMP, I'll get him onto it 

[MarshallJMP]

ok!