Sega Naomi 2 - RAM test sometimes bad

[prefabpeti]

Hello all, I have a really baffling Naomi 2 problem.

It plays N1 absolutely fine first of all. N1 RAM test always works.

I had suspected the N2 problems were down to overheating (random lock ups doing RAM test) and I had to replace the fan that wasn't always moving. I even went so far as to remove the N2 BGA heatsink with hot air and string, clean and reseat it with fresh glue/thermal compound.

Sometimes the RAM test completes fine with everything 'good', other times I get an error on IC107 and IC109 or just IC109.

Other times in just going to the BIOS menu I see the text is corrupted, the RAM test either hangs or with doing it enough times it actually fixes the text corruption.

Only today I had trouble getting to to start up, but just kept turning it off and on again until it would complete the RAM test. I'm now running a RAM test and powering off and on between tests - no 'bad' today!

Other times the Naomi logo is very slow to render or I get no display at all - but I have sound.

I've play tested VF4 (on Netdimm) and it'll run for between 5-20 minutes before either locking up or doing a go-slow.

The only pattern I can really see is if I can get a RAM test to work, it'll start a N2 game - but after a while of running that game - it'll go into its phase of not wanting to start again properly.

I can only think it's somehow those 2 RAM ICs - but is there any other tests I can possibly do before swapping them out?

 

[prefabpeti]

I did a lot of load testing yesterday - none marked as bad. But I had 2 lockups on VF4.

Machine came on again both times without too much trouble. Am I possibly fighting a power supply problem? This is an ATX Corsair power supply.

e.g.

View: https://www.youtube.com/watch?v=ush3R3p1xoQ


One of the comments:

I would strongly suggest to use an actual JVS power supply, 99.9% of ATX PSU (all except some very obscure platinum rated ones) share a single line between 5V and 3.3V, with usually sub par performances on those (because the main power draw on ATX runs through the (usually dedicated 12V line), this means when drawing current from 5V the 3.3V drops and vice versa, this also creates very large ripples which aren't suited for long term uses at all. Some systems are more tolerant than others, I would strongly suggest to NEVER use an ATX PSU with a NAOMI2 for instance, as it needs EXACTLY between 5.0 and 5.1V on load (that's 5.2V MAX off load), if you go over 5.2V on load you will eventually kill the NAOMI and NAOMI2 buffer chips, if you go below 4.8V the NAOMI2 will not get enough power on the 5V line and you will experience random crashes and various other issues/glitches. I should add that because you cannot regulate the voltage on an ATX PSU and only the 12V line is required to be on spec, you will see that the 5V and 3.3V outputs aren't exactly 5V and 3.3V but a slight variation of it, whereas JVS PSU are designed with potentiometers to let you exactly set the proper voltage using a multimeter. I strongly suggest to invest in a proper JVS PSU, you can either purchase a used SUN JVS PSU and recap it (as well as service/change the fan), or get the JVS supergun from axiunworks which acts as a universal JVS PSU, or get a Wei YA Viewlix JVS PSU. Heck, using a couple of (high amp) bench PSU is preferable to using an ATX PSU (albeit much more cumbersome and expensive). So, yes using an ATX PSU is cheap, it's just not a good thing for your JVS based hardware, better be safe than sorry. Feel free to verify all I have said by measuring voltages on and off load or even better, using a scope to see the huge ripples that occur while on load.

 

[MickyMac]

It looks like common bad ram chips. If one fails they show up bad in pairs.

Try reflow them (107/109) and if no luck then replace them.

Guide here for N1 but it's similar for N2:
Go 30 mins in:

View: https://youtu.be/yvZibLSguXM


I can't comment on what is the best power supply other then keep checking the 5v and 3.3v with multimeter or solder in a voltmeter. (Nobody sells a jvs plug in voltmeter). Personally I use original sun psu but they are getting old now.

 

[prefabpeti]

Thanks - what throws me is the RAM test doesn't always say its bad. Is this your experience too?

 

[MickyMac]

My experience was a hang at the ram test on a completely different ram too. Failed ram is extremely common in these.

 

[prefabpeti]

Thanks @MickyMac - the new power supply at least gives me the confidence my voltages are good. Error seems to happen much more consistently on those ICs now. I'll try a re-flow first, fingers crossed!