I still have to try to isolate exactly which component(S) have failed in an older Prostar816 Plus. No matter which phone is on the end of which line... or if there's only one phone, and everything else disconnected except the incoming CO lines... the "HOLD" function fouls up 3 of the 4 incoming CO lines. With (or without) a caller on line... press the "HOLD" button... and lines 1,2,3,4 will be unavailable for several seconds.
Line 5 seems unaffected. Usually. The longer you spend pushing CO line buttons... the longer it takes to recover. Best bet if you forget and hit "HOLD" is to just sit and wait for about 20 seconds. (If you had a caller, the line is dropped. They hear "click"... and then they're gone.)

I've played all the moving phones around stuff, disconnected everything, reset and reinitialized and re-entered all the programming I can several time to no avail. The only manual I have is the blue 82-page Installation Manual. Which seems about useless from this point on.

It sound to me like a problem on board somewhere, but I have no idea at all how to chase it down any farther.

Halp!
(ref the question "Fried Chips" on the other Sundance BB under Samsung for a few more details.)
Jason

Search on E-Bay "Samsung ProStar Plus". There's a 612 KSU there for 45 bucks. Have fun.

On page 35 of that manual it shows the mother board with the case open.

dip 2 ram ram battery and either a switch or a jumper with the ac plug removed either turn off
the switch or remove the jumper.

wait a while and reverse above and see if it is any better

is that cured it good
if not enjoy your ebay experience.

When you swap phones, problem follows phone or problem follows port? Or does problem occur on all ports?

Really stupid question: Are all of your amphenol cables off of the KSU attached tightly?

Ok (sorry about the slow reply)-first-
" remove the dipswitch wait a while and reverse above and see if it is any better is that cured it good if not enjoy your ebay experience"
*** not so good. Ebay time? what are we hoping to do.... ? Doesn't that just make sure we've done a hard reset, a full power down?****

Second question-
"When you swap phones, problem follows phone or problem follows port? Or does problem occur on all ports?"

***problem occurs on all ports that have lines attached EXCEPT CO #5 (usually)... which is a single line port. We use CO's 1-6, seven and eight are unattached. Considered splitting up the dual pairs (1,2 and 3,4) thinking it may be a port problem, but don't have enough single ports to hae them all plugged in at once. (Doesn't seem to change anything when I move single 5/6 to single 7/8 anyway... seems to be a problem in the dual port inputs... because it still happens on 3/4 when 1/2 are unplugged, and on 1/2 when 3/4 are unplugged... and those are all on the main board, right?

To prove that it was not a single phone / line combination that was creating the weirdness, I moved the keyset phones from line to line, and tried it out with all in house lines unplugged except the line to whichever phone I was using. Same results, on each line I tried... no matter which phone was on the end of that line.

"Really stupid question: Are all of your amphenol cables off of the KSU attached tightly?"

Yep. All the RJ connectors look good. Pulled them out and put them back, several times, they're all in properly. Don't see any burned ones / loose ones. Checked out the punches where they split from the CO bundle to the 66blocs, too... just in case.
Jason

One interesting note... after pressing hold, when you try select a CO line, the "beep" noise it makes sounds suspiciously like there's a bit of feedback to it... a quick sharp "ssqueak" followed by a "blip" and ... the line is gone.
The feedback noise occurs whether you are using the the speakerphone, or the handset...
Jason