Memory problem with Centris 610

[wilykat]

I have a bunch of memory sticks and I wanted to kick up my Centris to max 68MB but something isn't working right.  A 16MB SIMM shows up as 8. A 32MB SIMM shows up as 8.  I put in 2x32MB, it shows a grand total of 20MB (4MB onboard plus 2x8MB)  I tried mixing and matching and I tried one at a time in either slot.  It seems to be always 8MB if I used anything larger than 8MB.

CPU problem? or where to start looking for trouble?  Right now it's like a Porsche that is limited to top speed of 20 MPH because it won't go past second gear.  

 

[Byrd]

Is the RAM matched, EDO/FPM, double sided?  Point the finger at the modules, not the Mac I reckon.

 

[wilykat]

2 16MB are both double sided FPM same brand, 2 8MB are matching double sided I suspect EDO.  2 32MB are both single sided PNY brand EDO.

I've tried one at a time and still got max 8MB in any slot.  A single memory stick shouldn't be having problem showing full amount.

 

[trag]

You should be able to install two 32 MB SIMMs without any hacking. The 32MB SIMMs need to be two-bank SIMMs. That means that they have two sets of 16MB memory on-board, which share data and address lines and use different pairs of RAS lines. If they are single-bank 32MB SIMMs they won't work. I've never seen a single bank 32 MB SIMM, but they could exist.

Your two-bank 32MB SIMM should, typically, consist of 16 memory chips, each 4M X 4. Eight of them form one bank as 4M X 32 bits. The other eight form the other 4M X 32 bits. 32 bits = 4 bytes, so each bank is 4M X 4bytes = 16MB and with two banks on a SIMM, you get 32 MB.

If your 32 MB SIMMs are made out of eight 8M X 4 memory chips, then you might have a single bank 8M X 32 SIMM.

You can discover what kind of memroy chips your SIMMs have by reading the part number off of the memory chips and looking for a datasheet for them on-line -- usually at datasheetarchive.com. Manufacturers usually don't have datasheets that old available any more.

If you want, I can send you a pair of 32MB SIMMs that should work. If they work, you can send me $10. If they don't work, send them back. PM me if you would like to to do that, but it sounds like you have a lot of 72 pin memory on hand already.

 

[wilykat]

Thanks for the offer. I am waiting on the offer for free Quadra 700. If I get it, I'll leave my C610 stock and play with Q700 instead.  Q700 uses older 30 pins SIMM and AFAIK there is no 72 pins to 4x 30 pins adapter to let me use cheaper 72 pins SIMM in older Macintosh.

 

[wilykat]

One SIMM I checked has mcm514256 x8 on one side which seems to be 4 bit x 256Kb? Or 1MB total. Might explain why my C610 never worked with it, it's either meant for really early 32 bit computers or printer?  Another SIMM has 4x hyb5117800asj which is 8 bit x 2Mbit or 8MB total which my C610 detected correctly.

Reading chip number is hard even with magnifying glass. Finding answer with Google is much harder because the first 50 or so hits are often by Chinese chip sellers who are offering chips by the part number but not identify what it is, or have the datasheet. It's like these Chinese sellers are farming chips number and are hoping someone would stumble on them looking to buy chips.  Some of the hits also leads to datasheet sites who claims to have it and won't let me read it unless I buy them. No guarantee it'd be the right one or even one that's not a fake.