SE/30: Capacitor testing but maybe a Memory issue

[Elysiom]

My SE/30 has close to 20MB of memory installed... yes odd number but it's what System 6 is reporting (fresh install, wiped HD) to my knowledge System 6 didn't have any "virtual memory"

The memory isnt labeld in anyway but I'm guessing the configuration is

4 x 1 MB and 4 x 4MB SIMMS

Sometimes on boot it will display a Simasi pattern... but only some times and if I hit reset enough times it will boot like nothing is wrong which leaves me to believe there may be an issue with the memory

Another issue is that the sound is very low / no startup chime which directly points at a capacitor issue, is there a way to test the caps on the board? It's been a while since I have used an ohmmeter but I believe you check that they don't have an infinite amount of resistance

I did pull the board and I didn't see any leaking electrolytes but that certainly doesn't rule out an issue with caps, the board is actually super clean for it's age

Thanks to every one for your time and sorry if this is a repost

 

[macgeek417]

Try holding down the mouse while booting - if it boots normally, then its just the fact that if has a lot of RAM.

 

[JDW]

I didn't see any leaking electrolytes...

Read this:

http://68kmla.org/forums/viewtopic.php?p=57710#57710

And the "sticky" that's unfortunately not so sticky:

http://68kmla.org/forums/viewtopic.php?p=57777

And my closing remarks here:

http://68kmla.org/forums/viewtopic.php?p=73596#73596

 

[Elysiom]

Ok, dumb question time

RadioShack has 47µF 35V (it's Electrolytic) I'm not familiar with SE/30 board enough... could I use it to replace C7 which is a 47µF 16V? The RadioShack one has a tolerance of +_ 20

 

[JDW]

47µF 35V (it's Electrolytic)... could I use it to replace C7 which is a 47µF 16V?

The tolerance spec is largely irrelevant. Yes, you can use the high voltage rated cap. Just don't go lower than the stock part and you will be fine. And keep in mind that you can use longer-life tantalum caps too in that size. You will never have to replace a tant, but you will (maybe in 15 years) with an electrolytic.

 

[Elysiom]

Well good news, I replaced C6 and C7 and I got video working properly again

Sound is still low (so low that I can't hear any bong on startup), hopefully replacing the rest of the capacitors will fix that

 

[Unknown_K]

I have a SE/30 with no sound waiting for some capacitors to arive to redo it. That unit works fine video wise.

Tants will last a long time, but even they have a lifespan and I think they tend to short when they go. I use whatever Apple originally used when I recap motherboards. I read somewhere that Aluminum capacitors like the ones we are replacing have a life or 2000 or 4000 hours of use (forget the exact number), so if they lasted 10+ years of constant use they will last forver of little use in our collections.

Thankfully the 68K macs tended to use a small variety of values for capacitors, 47uf 16v, 100uf 6.3v, 10uf 16v come to mind.