First post, by rickdeckard
Hi, guys!
So, I've recently come across this motherboard - the A-Trend ATC-1020. The motherboard is said to support regular Pentiums as well as MMXs, but as I understand from TheRetroWeb's pictures and description, there are at least 2 revisions of this board, as it's obvious looking at its bottom-right corner:
- one with the CPU's core and I/O voltage planes jumpered together from factory (picture posted by "old_pc_parts" on TRW), namely JP11, JP12 and JP13; this supplies 3.3V on both the core and I/O side of the CPU;
- another with the core and I/O planes separated by a physical jumper JP11, with a separate voltage regulator for the core voltage (picture posted by "computerguy096" on TRW).
As mentioned, the area in question is the bottom-right corner. On both revisions, the layout of the PCB is very similar, in the sense that the planes are separated, but out of the box, only the second revision supports MMX CPUs since the other one has the planes solder-jumpered together supplying 3.3V to both the core and I/O pins and is missing the voltage regulator for the CPU core voltage. The board manual also unfortunately only shows the layout of the second revision, listing all the options for setting up dual-voltage CPUs and such.
Now, the reason for this post is that the motherboard I have is the first revision, the one that has the planes soldered together and is missing the voltage regulator. As you can see in this picture here -
I've removed the JP11, JP12 and JP13 soldered jumpers and added headers for regular jumpers (yellow in my picture) and with these jumpers removed, the core and I/O voltage planes are indeed separated as expected. I can manually feed 2.8V on the pins connected to the other plane (didn't do that yet - I'm not sure what how many amps these CPUs pull on the core side and I don't want to risk it; might try it tho). However, obviously there's no voltage regulator to drive the core side of the circuit, which is what I'm here for.
Is there anyone here that has the other, "complete" revision of this board, which has the elusive core voltage regulator and the rest of the circuit for the dual-voltage core side of the circuit, and can help me with the part numbers for these parts? A close-up picture of this area of the board should be enough for me to figure it out from there. I think there's also an IC (U28) involved, which I think I'll need to source as well, and maybe a resistor or two. Also, no clue what JP15 and JP16 are for, there's no mention about those in the manual (they also seem to be missing from the "good" revision of the board).
P.S.: do I have other boards that I can use with MMX CPUs? Yes. Do I need to make this one work? No, not really. Do I want to? Hell yeah. It's just that dude, it's so close to being a damn nice board, it's like a marathon runner missing a toe and I can't sleep well at night until I can have it running with an MMX CPU.
