On Tue, Feb 2, 2021 at 12:30 AM Josh Dersch <dersc...@gmail.com> wrote:
> > > On Sun, Jan 31, 2021 at 10:03 PM Fritz Mueller <fri...@fritzm.org> wrote: > >> >> >> > On Jan 31, 2021, at 8:19 PM, Josh Dersch <dersc...@gmail.com> wrote: >> > Well, what's interesting here is that on my system, switch S4 (MAINT >> STPR) steps the processor with switches S1 and S2 set to *any* >> configuration. >> >> Hmm, would expect to see S2:1 S1:0 step by microinstruction, and S2:1 >> S1:1 step by clock phase. The other two settings should free run the >> microcode. So yeah, sounds like something fishy there... The TIG card has >> more than a few analog components, and its not too unusual for these to get >> hung up on the adjacent card and have a leg pulled or sheared from the >> board. >> >> > Ah, and page II-6-20 (p. 178) indicates that when DCLO is asserted, it >> asserts: "UBCE ROM INIT H - forces the ROM to ZAP.00 (200), and stops and >> clears the Timing Generator and the Cache timing." >> >> Yup, that's one of the signals coming in to RAC E106. Probing there >> should indicate which of possible sources for ZAP is actually occurring >> (UBCE ROM INIT H on pins 2 and 3 there). >> >> DCLO is a classic... Make sure to 'scope it, because it sometimes has >> troublesome spikes that don't show on a multimeter. If you have H742s, >> there are some wet tantalums on the control board that sometimes leak and >> cause trouble with this. >> >> I'm sure you are raring to go -- hope those fans show up for you >> tomorrow, and will be interested to hear what you find! >> > > > Small update; fans arrived today and they are now installed. Voltages > tested on the backplane at the points called out in the service docs, and > all voltages dialed in to 5.05V. Ripple is within tolerances -- about > 200mV with some very short spikes that barely show up on my 'scope that go > to 300mV or so. Not sure if this is abnormal, I also saw these while > burning the supplies in on the bench. > > Checked the AC LO and DC LO signals at all the points called out in figure > 6-12 (p. II-6-22 of > http://bitsavers.org/pdf/dec/pdp11/1170/EK-KB11C-TM-001_1170procMan.pdf) > and appear to be correct. Looked at most of them under the scope and no > spikes (other than those in the ripple from the power supply.) > > Tomorrow I'll get some boards out on extenders and take a look at what's > going on at the logic level. > Another quick update: Had some time last night to poke at things. I started with the TIG, since I wanted to see if the crystal clock was running at all and if the right clock source was being selected. Sure enough, TIGB XTAL H was a flat line. Nothing happening at the crystal itself either. The crystal's casing was fairly corroded (which is interesting, since nothing else on the board is) and after a tiny bit of prodding one of the legs fell off, so I'm hoping that's the culprit. New crystal ordered and when it arrives we'll see... - Josh
