MiSTer FPGA Forum

Hello dear people of the MiSTer forum

I've built two 128SDRAM boards but the frequency at which they operate is different.

The 1st module i've built can run memtest for at least two hours at 150Mhz without any failures and i've played a lot of systems on it as well all without any issues.

The 2nd module i just built now runs memtest at 140Mhz, but 150 produces failures within seconds, at the moment of writing it has run memtest for 20 minutes without any failure.
I'd probably test some systems and games with them as well to see if it runs ok, most likely the bad apple demo as there's no other system that fills the RAM that far yet if i remember correctly?

But is this a normal phenomenon and is there a minimum frequency the modules should pass to be quality modules?

If anyone could chip in i would greatly appreciate your feedback!

Thanks in advance!

As far as I know, 130 MHz is considered the baseline for an acceptable board (due to the Archie core running SDRAM at 126 MHz), and the more reputable sellers test at 140 just for some extra margin.

I've ran the memtest for 125min. without any issues, so i guess it can differ from chip to chip then?
The bad apple demo from Neo Geo ran perfect as well and i'm playing a few games on different cores all without any further issues.

The 150Mhz chip board can be considered higher quality chips then or is there any other specific reason why it could run at lower speeds?

Odd thing i noticed now when retesting my boards i made, they dropped 10Mhz in frequency in which they can operate so the 150 dropped to 140 and the 140 dropped to 130?

Nothing has changed in my MiSTer setup though and i've cleaned the contacts on both sides with isopropanol but the 10Mhz drop is still there.

MostroW wrote: ↑Fri Aug 28, 2020 2:54 pm Odd thing i noticed now when retesting my boards i made, they dropped 10Mhz in frequency in which they can operate so the 150 dropped to 140 and the 140 dropped to 130?

Nothing has changed in my MiSTer setup though and i've cleaned the contacts on both sides with isopropanol but the 10Mhz drop is still there.

Do pins have good contact? This video seems to imply the pins have an impact:
Mem Test 150 Mhz passed thanks to shorter pins!

Well these modules have worked on 150Mhz and 140Mhz before i retested them, and in the span of two weeks or so they degraded without anything changed to either module or the DE10.
That's what surprised me, so i thought maybe it could be dirty contacts but i've cleaned them, i could try contact spray maybe but i don't know if that is a really good thing to try.

MostroW wrote: ↑Fri Aug 28, 2020 6:46 pm [...] i could try contact spray maybe but i don't know if that is a really good thing to try.

Not my area of expertise. I only use contact cleaner for things like pots or battery contacts.