ah, welcome to the club! hehehe
 a large number of KA650's dont play nice with TK50s. I pulled my hair out
for days trying to figure this one out, going through 3 or 4 TK50 
controllers, 4 or 5 drives, and two processors trying to find a 
combination that worked. It turns out that most early-rev KA650's have a 
problem talking to TK50 controllers. One solution is o use a TK70 
controller, though that didn't work for me, the thing that did was to 
just use a KA630, as you also discovered.  there was some discussion 
about this maybe 6 or 7 months ago on the list... check the archives. 
happy hacking,
isildur

On Tue, 29 May 2001, NetBSD Bob wrote:

> I was playing around with my BA123 box last night trying to write some
> TK50 tapes, and ran into an interesting problem.  The machine had a
> KA650 boardset with 32mb ram.  The TK50 would not write reliably at all.
> It would barely read reliably from my master tapes.  I pulled the KA650
> boardset and dropped in the original KA630 boardset.  The TK50 ran fine.
> Is there something borderline about the quality of a BA123 backplane
> running at 3 vups vs 1 vup?  I was wondering why I was having so much
> problem with TK50 tapes lately, and it appears to be bus speed related.
> In the early S100 days, we used passive bus terminator networks to
> calm the bus a 4mhz.  I noticed that my 4000/200 has a bus terminator
> card in it.  Should the BA123 have such a terminator board in it?
> If so, which board, and where do I find one?  Any other suggestions
> about TK50 bus speed related problems?
> 
> Thanks
> 
> Bob
> 
>