> -----Original Message----- > From: cctalk [mailto:[email protected]] On Behalf Of Robert > Jarratt > Sent: 05 December 2015 19:49 > To: 'General Discussion: On-Topic and Off-Topic Posts'; > [email protected] > Subject: RE: Memory Voltage on MicroVAX II > > > > -----Original Message----- > > From: cctalk [mailto:[email protected]] On Behalf Of Jon > > Elson > > Sent: 05 December 2015 19:19 > > To: [email protected]; [email protected]:On-Topic and > > Off- Topic Posts > > Subject: Re: Memory Voltage on MicroVAX II > > > > On 12/05/2015 12:29 PM, Robert Jarratt wrote: > > >> -----Original Message----- > > >> From: cctalk [mailto:[email protected]] On Behalf Of > > >> Jon Elson > > >> Sent: 05 December 2015 18:03 > > >> To: [email protected]; [email protected]:On-Topic and > > >> Off- Topic Posts > > >> Subject: Re: Memory Voltage on MicroVAX II > > >> > > >> On 12/05/2015 09:51 AM, Robert Jarratt wrote: > > >>> I finally fixed my H7864 PSU so I can now run my rtVAX 1000. > > >>> However, I think the machine is damaging memory boards. I checked > > >>> the ripple and 5V looks OK, but 12V looks suspicious. Is the 12V > > >>> supply used by the > > >> memory? > > >> I don't have my print set anymore, but I highly doubt it. I think > > >> the +/- > > > 12 V is > > >> only used by serial comm boards, and possibly by some graphics > > >> boards. I would not be surprised if the regulation of the 12 V > > >> supplies is not very precise. > > >> > > >> Jon > > > There seems to be a spike on the 12V supply, surely that isn't good, > > > even if it doesn't affect the memory? > > > > > > > > How BIG a spike? In a lot of these power supplies, they don't > > regulate > the > > "auxiliary" voltages. So, whatever power is needed to be sent to the > > main voltage, the aux. windings just tap off some of that energy. If > > the flux produces the right voltage on the +5V (with so many turns on > > that > > winding) then they put a few more turns on the 12 V windings, and > > assume > it > > should track FAIRLY well. But, maybe during the power-up surge, > > charging > all > > the caps on the +5 network, the +12 might surge a bit. > > > > I built my own power system on my uVAX-II system, and had separate > > supplies for +5 and +12 (mostly for the disk drives). One day the 12 > > V > supply > > went haywire, and I had inadvertently disabled the crowbar circuit. > > It > went > > up to > > 22 V and damaged the disk drive and blew caps and the RS-232 driver on > > the CPU board. The disk drive worked for another week, and then > > totally croaked. I ordered the parts for the serial transmitter and > > got it fixed > fairly > > easily. (He he, glad I had that print set!) > > > > So, I can say that if the spike gets close to 22 V, that would be real > bad. > > > > Jon > > I would have to measure again, but I don't think it was anywhere near that > big a spike. I did measure the ESR on the capacitor on that output and it > seems OK, although marginally higher than the same cap on some of the > other outputs, so I am thinking of replacing it anyway. > > As the 5V seems fine, the ripple seemed to be about 20mV (although I am > going to check again), I do wonder what could be causing the memory > modules to appear to be failing. I am hoping that re-seating will cure it. > > Regards > > Rob
Checked ripple again and 5V is fine, and 12V is actually not that big. Putting the memory back in, it started to work. So it just needed re-seating. Phew! It all works now, I have a working rtVAX 1000. Now it is time to find out what it can do. Regards Rob
