kim@amdahl.amdahl.com (Kim DeVaughn) (10/19/87)
[ There ain't no such thing as a free line. ]
I've been burning-in my B2000, and have noticed that accuracy of both the
normal internal clock (timer, really) and the battery-backed-up RTC are
unacceptable.
Can someone at CATS (Dave, George, Carolyn) please tell me if/where the
trimmers are so I can get these clocks running right? I'd prefer not to
have to go thru the hassle of returning the machine to the dealer for just
an adjustment.
Though it should not matter, I have a 68010 in the machine (you *don't* have
any s/w timing loops in there, do you?)
In case you're interested, here are the numbers (all +/- 1 sec.):
Internal clock/timer:
204 sec. slow in 69,520 sec.
302 sec. slow in 102,600 sec.
Or approximately 0.29% SLOW.
RTC:
61 sec. fast in 103,060 sec.
Or approximately 0.06% FAST.
Why aren't these locked to the line frequency, which has very good long-term
accuracy, though may suffer from short-term stability?
/kim
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CIS: 76535,25kim@amdahl.amdahl.com (Kim DeVaughn) (10/19/87)
[ Some days you eat the line ... some days the line eat's you ... ]
In an earlier posting, I mentioned that both the timer and RTC in my B2000
were overly inaccurate. After making the posting (naturally), I remembered
that there were schematics in the back of the manual, and although they are
for the A2000 (?), I decided to take a look.
Sure enough, they showed a jumper going to one of the 8520 timer chips, and
a small variable cap in the oscillator feeding the Oki 6242B clock/calendar
chip. Also, the Manual Update sheets said that the J300 jumper was used to
select the time-base for the 8520 between the line-driven TICK signal (50/60
Hz), or the vertical sync pulse for the video section. The default position
of the jumper is *supposed* to be the TICK signal. Since this description
agreed with the schematic, I decided to open the box up for a look.
Naturally, the J300 jumper is underneath the power supply, but the sub-frame
holding it and the drives comes out easily ... just 6 screws, and a couple of
connectors (thanks!)
Yep ... the jumper was between pins 2 and 3 rather than the pictured default
between pins 1 and 2! So the timer chip had been getting popped at the
vertical sync rate, rather than being locked to the line frequency. No big
deal, just swap the jumper. Now the question is ... why would one want to
drive the timer from the vertical sync, rather than from the line? Maybe
for use in areas with ill-controlled power?
And there was indeed a small trimmer cap near the Oki chip (just in front of
the 86-pin coprocessor slot). No markings to tell which way to go, but it's
a 50-50 shot ... I tweaked it a hair CCW (is that the correct way to turn it
to slow it down, Dave?) We'll see ...
BTW, it would be nice if the RTC were locked to the line freq. when the machine
is plugged in (or at least is powered on), and switched to using the xtal
oscillator only for battery backup, but I guess that'd be too expensive.
Anyway, if your clock(s) aren't keeping the right time, and particularly
if the timer driven system clock is running about 0.3% slow, you now have
a couple of things to check out.
/kim
P.S. FYI ... the Fat Agnus chip is called "FAT LADY" on the silk-screening,
and for some reason, Buster isn't named, though Gary, Paula, and Denise
are (this is on a rev 4.2 board).
--
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CIS: 76535,25dillon@CORY.BERKELEY.EDU (Matt Dillon) (10/19/87)
>RTC: > 61 sec. fast in 103,060 sec. >Or approximately 0.06% FAST. > >Why aren't these locked to the line frequency, which has very good long-term >accuracy, though may suffer from short-term stability? Well, you can't have the battery backed clock on the line freqency... the whole point is that it still keeps time even when your Amiga is unplugged. 61 secs / 103060 secs = (86400 secs/day)... about 40 seconds a day. This is incredibly bad! Obviously the crystal used to run the battery backed clock is not being tuned at the factory. (I don't have one yet so this is a guess)... at least, they had *better* be crystals and not ceramic resonators. -Matt
andy@cbmvax.UUCP (Andy Finkel) (10/20/87)
In article <16531@amdahl.amdahl.com> kim@amdahl.amdahl.com (Kim DeVaughn) writes: >Yep ... the jumper was between pins 2 and 3 rather than the pictured default >between pins 1 and 2! So the timer chip had been getting popped at the >vertical sync rate, rather than being locked to the line frequency. No big >deal, just swap the jumper. Now the question is ... why would one want to >drive the timer from the vertical sync, rather than from the line? Maybe >for use in areas with ill-controlled power? > This makes it compatible with the A500 which doesn't have the tick coming from the power supply :-( but must rely on the vertical sync line for its timing, which we know is......... andy -- andy finkel {ihnp4|seismo|allegra}!cbmvax!andy Commodore-Amiga, Inc. "Interfere? Of course we'll interfere. Always do what you're best at, I always say." Any expressed opinions are mine; but feel free to share. I disclaim all responsibilities, all shapes, all sizes, all colors.
daveh@cbmvax.UUCP (Dave Haynie) (10/22/87)
in article <16516@amdahl.amdahl.com>, kim@amdahl.amdahl.com (Kim DeVaughn) says: > Keywords: I hope there are knobs in there > > [ There ain't no such thing as a free line. ] > > I've been burning-in my B2000, and have noticed that accuracy of both the > normal internal clock (timer, really) and the battery-backed-up RTC are > unacceptable. > > Can someone at CATS (Dave, George, Carolyn) please tell me if/where the > trimmers are so I can get these clocks running right? I'd prefer not to > have to go thru the hassle of returning the machine to the dealer for just > an adjustment. OK, here goes. The trimmer for the RTC is relatively easy to get at with just the box top off. You'll need a "tweaking tool", which usually looks like a long piece of plastic with a thin metal tip (for those out there not familiar with this sort of high-tech equipment....). The trimmer is located just a hair to the south of the Coprocessor slot. It should be possible to adjust this to be about as accurate as a digital watch, as the clock chip uses a common watch battery. They're supposed to be adjusted on the production line, though it's certainly possible that some fall out in shipping and all. There will probably be a slight varience in the clock frequency depending on whether or not the unit's powered on, I don't know how much this varience can amount to. As for the internal system clock, that is based on the 60Hz tick from your line voltage. Or SHOULD be. Because in fact, the B2000 can be internally jumpered to count time off the vertical sync line, just as the A500 does. This is all controlled by J300, which is (you guessed it) hidden under the power supply. It's the jumper just a bit to the North of the Paula chip, if you do happen to open your machine up and look inside. These are supposed to be shipped in the line Tick position, which means the shunt plug is to the left. If this is installed properly, the only other thing that could affect your timing here is lousy line frequency regulation in your area. > Though it should not matter, I have a 68010 in the machine (you *don't* have > any s/w timing loops in there, do you?) I've got one too, and as far as I know, my clocks stay pretty accurate. > Why aren't these locked to the line frequency, which has very good long-term > accuracy, though may suffer from short-term stability? The OS clock is, or should be, but that only works when the machine is on. The RTC can't be, or it would lose its time base if the power went out or you moved the machine. > /kim -- Dave Haynie Commodore-Amiga Usenet: {ihnp4|caip|rutgers}!cbmvax!daveh "The B2000 Guy" PLINK : D-DAVE H BIX : hazy "Computers are what happen when you give up sleeping" - Iggy the Cat
jdow@gryphon.CTS.COM (Joanne Dow) (10/23/87)
In article <2572@cbmvax.UUCP> daveh@cbmvax.UUCP (Dave Haynie) writes: >in article <16516@amdahl.amdahl.com>, kim@amdahl.amdahl.com (Kim DeVaughn) says: > >> Why aren't these locked to the line frequency, which has very good long-term >> accuracy, though may suffer from short-term stability? > >The OS clock is, or should be, but that only works when the machine is on. The >RTC can't be, or it would lose its time base if the power went out or you >moved the machine. > Ah well padnah it can be done. Some years ago I had a clock chip for my amateur radio station (lost in subsequent moves...) that accepted line frequency clocks until they died. Then, with a loss of perhaps two or three clocks, it picked up from an internal clock. Thus I was able to leave it on continuously and as long as line frequency remained it remained line synched. Once it was unplugged or the lines went down the local "clock" kept it to reasonably close time. Howsosomeever that'd add perhaps a dozen bucks worth of parts and assembly time to the A2000/A500 and if we do that enough we could price the fool things up into the Mac levels of the stratosphere. > /kim >-- >Dave Haynie Commodore-Amiga Usenet: {ihnp4|caip|rutgers}!cbmvax!daveh > "The B2000 Guy" PLINK : D-DAVE H BIX : hazy > "Computers are what happen when you give up sleeping" - Iggy the Cat -- <@_@> BIX:jdow INTERNET:jdow@gryphon.CTS.COM UUCP:{akgua, hplabs!hp-sdd, sdcsvax, ihnp4, nosc}!crash!gryphon!jdow Remember - A bird in the hand often leaves a sticky deposit. Perhaps it was better you left it in the bush with the other one.
kim@amdahl.amdahl.com (Kim DeVaughn) (10/30/87)
In article <2541@cbmvax.UUCP>, andy@cbmvax.UUCP (Andy Finkel) writes: > In article <16531@amdahl.amdahl.com> kim@amdahl.amdahl.com (I) wrote: > > >Yep ... the jumper was between pins 2 and 3 rather than the pictured default > >between pins 1 and 2! So the timer chip had been getting popped at the > >vertical sync rate, rather than being locked to the line frequency. No big > >deal, just swap the jumper. Now the question is ... why would one want to > >drive the timer from the vertical sync, rather than from the line? Maybe > >for use in areas with ill-controlled power? > > This makes it compatible with the A500 which doesn't have the tick > coming from the power supply :-( but must rely on the vertical > sync line for its timing, which we know is......... Strange that it (the 500) doesn't pick off the line frequency ... doesn't seem like much of a cost savings not to. An "interesting" side effect of changing the jumper from the video sync to the line tick, is that my floppy now *grinds* noticibly LOUDER (gak!) Everything is nice and tight, mounting wise, so it must be due to the slight difference in timer interrupt rates (resonance ?) Sounds pretty fishy, but I don't have a better explanation ... Last night, I installed a 2nd 3.5" floppy, and *it* is REALLY quiet ... literally, quiet as a whisper. It's the exact same Matsushita drive (model, assembly level, etc.) as df0: but *much* quieter than df0: was even before I changed the timer jumper! Oh well ... /kim -- UUCP: kim@amdahl.amdahl.com or: {sun,decwrl,hplabs,pyramid,ihnp4,uunet,oliveb,cbosgd,ames}!amdahl!kim DDD: 408-746-8462 USPS: Amdahl Corp. M/S 249, 1250 E. Arques Av, Sunnyvale, CA 94086 CIS: 76535,25
grr@cbmvax.UUCP (George Robbins) (11/15/87)
In article <17264@amdahl.amdahl.com> kim@amdahl.amdahl.com (Kim DeVaughn) writes: > > > > This makes it compatible with the A500 which doesn't have the tick > > coming from the power supply :-( but must rely on the vertical > > sync line for its timing, which we know is......... > > Strange that it (the 500) doesn't pick off the line frequency ... doesn't > seem like much of a cost savings not to. Well, all A500 power supplies are switching supplies, and one class of switcher, the kind that rectifies the line current directly and puts the isolation transformer after the switching circuitry, doesn't have any convienient 60 Hz transformer where you can pick up the line frequency tick. There were some alternatives but they all seemed to do disproportionate things to the cost of the supply, cable and connectors. > An "interesting" side effect of changing the jumper from the video sync to > the line tick, is that my floppy now *grinds* noticibly LOUDER (gak!) > Everything is nice and tight, mounting wise, so it must be due to the > slight difference in timer interrupt rates (resonance ?) Sounds pretty > fishy, but I don't have a better explanation ... This is flatly and completely impossible!!! Meaning I guess we should try it here and see if we see the same kind of effect. One possibility would be that using the vertical sync signal the clock related software activity is always synchronized to the video related activity, whereas in the line frequency it would tend to gradually drift in and out of sync. > Last night, I installed a 2nd 3.5" floppy, and *it* is REALLY quiet ... > literally, quiet as a whisper. It's the exact same Matsushita drive > (model, assembly level, etc.) as df0: but *much* quieter than df0: was > even before I changed the timer jumper! Oh well ... Life is strange... -- George Robbins - now working for, uucp: {ihnp4|rutgers|allegra}!cbmvax!grr but no way officially representing arpa: out to lunch... Commodore, Engineering Department fone: 215-431-9255 (only by moonlite)