is there a way to thoroughly test RAM in Solaris10 (SPARC)?
or is boot test good enough?

Normally booting and running Solaris will tell you soon enough if you have a hardware problem.

If I really suspect that my hardware is sick in some obsure way then I install SunVTS (Google that) to run extensive diagnostics.

The normal diagnostics are pretty good, if you want to you can run an extended diagnostics upon boot which is even more thorough. The normal diags take maybe 10 minutes to run and the extended will be around an hour. Well, at least that's on my servers, yours may have more or less equipment and the times will change accordingly.

You may also wish to review the FreeBSD for Sparc page which may allow you another testing environment.

thanks.
our servers are quite old, and we might have to use used RAM.
is there a risk of physical damage to server if RAM modules are faulty?

Well there are no guarantees but damage to the server is very unlikely especially if the RAM is known to be the right type (eg, voltage, etc).

Do your research; stuff the part numbers, etc into Google and see if that comes up with the specification.

Talking generically, RAM needs a voltage supplied by the motherboard. Typically 5V or 3.3V. If the motherboard supplies 3.3V and you fit a 5V module it won't work (but might just unreliably). If the motherboard supplies 5V and you fit a 3.3V module it will fry the module but shouldn't damage the motherboard.

Fitting a correct but faulty RAM module won't do any damage but will fail diags. Voltage is the important thing. Obviously the RAM architecture needs to be right too for it to work, but generally different architectures have different edge connectors.

TIP: Of course if you're working with suspect RAM modules fit one at a time to see if they work. Test one for a while, then add a second, and so on.

ALSO....consider that the memory socket on the motherboard might be faulty - not the RAM module. Process of elimination I'm afraid.

Another quick way to see if you hardware issues to reboot the server running extend post on reboot. This does a comprehensive review of your hardware. Sorry if jumped into this a bit late.