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Amiga computer related discussion => Amiga Hardware Issues and discussion => Topic started by: Malakie on December 19, 2021, 04:05:32 AM
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This machine is driving me nuts.. one thing after another.. but I AM going to get it fixed and running properly.. someday.
This one is the real time clock running too fast. It is counting seconds way too fast in fact. 2 minutes on my watch or a pc, is coming out to about 3 minutes 15 seconds on this unit. Figured I would ask to see if anyone has come across this one before I go diving into components and schematics.
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Trim pot just in front of the CPU card slot, left of the RTC battery.
OK, it's a varicap really, Labelled VC880 or similar.
EDIT: It's further over to the left on a rev 6 A2000, in front of the first Zorro socket. But I recall you had V4.
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Doesn’t A2000 use PSU "tick"? Is this a PAL A2000 in NTSC land? :)
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Doesn’t A2000 use PSU "tick"? Is this a PAL A2000 in NTSC land? :)
No, Malakie did specify real time clock, fitted in all A2000s.
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I find the term "real time clock" misleading. The CIA TOD clock also measures real time, once it's set. "battery-backed up clock" is more precise. That's also the wording SetClock uses if it does not find one.
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I'd agree with Thomas; the battery backed up clock is read once by the system at startup (if found), and from then the time of day counter is responsible for maintaining the system time after startup.
If the problem is that the time drift happens with the computer is powered off, then it's likely to be a battery backed up clock issue. I've written test/calibration procedures for that here:
http://amiga.serveftp.net/RTCrepair.html#OscillatorCalibration
If the time drift is while the computer is powered on, then it could be a problem with the hardware timers. Use Amiga Test Kit to sanity check the CIA timers:
https://github.com/keirf/Amiga-Stuff
There could be an issue with the 28.3MHz oscillator, as the time of day counter is derived from this on many Amiga models; though if the clock is drifting that much, you'd probably have seen video issues if the 28.3MHz reference was that far out.
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Trim pot just in front of the CPU card slot, left of the RTC battery.
OK, it's a varicap really, Labelled VC880 or similar.
EDIT: It's further over to the left on a rev 6 A2000, in front of the first Zorro socket. But I recall you had V4.
ahh that's right.. I knew that but until you said something, I had completely forgot about that.. This board I will be able to correct I hope but the next one.. I will have to replace that as the battery exploded on that board I got from someone and that pot is corroded badly.
The good news, my V6 boards, I have two, are in the best shape of everything I have thankfully. What I am trying to get going are older 4.x boards with various problems. Two so far running good, one with v1.3 OS/A2090 w/st-506 drives, the second 2.04 OS and A2091 with SCSI drives, this nightmare unit is supposed to be 3.2 os with A2091 SCSI, another identical board has a GVP HD board and GVP 68030 w/daughter ram board (note identical rev 4.x and this one runs perfectly with SCSI drives which makes me think you are right and it is either a scsi.device issue in KS3.2 or the 7.0 roms) and then the two rev 6 units, one using the PI-Raspberry upgrade, the other I had intended on doing another A2091 SCSI setup with 3.5/3.9 updates to it.
So thanks for the help and reminders! Amazing how much one does not really forget but gets pushed to the archives of long term memory until nudged! LOL
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I'd agree with Thomas; the battery backed up clock is read once by the system at startup (if found), and from then the time of day counter is responsible for maintaining the system time after startup.
If the problem is that the time drift happens with the computer is powered off, then it's likely to be a battery backed up clock issue. I've written test/calibration procedures for that here:
http://amiga.serveftp.net/RTCrepair.html#OscillatorCalibration (http://amiga.serveftp.net/RTCrepair.html#OscillatorCalibration)
If the time drift is while the computer is powered on, then it could be a problem with the hardware timers. Use Amiga Test Kit to sanity check the CIA timers:
https://github.com/keirf/Amiga-Stuff (https://github.com/keirf/Amiga-Stuff)
There could be an issue with the 28.3MHz oscillator, as the time of day counter is derived from this on many Amiga models; though if the clock is drifting that much, you'd probably have seen video issues if the 28.3MHz reference was that far out.
Something I should have clarified, the drift does happen at power off. BUT while the unit is running, it is also running fast.
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Just an update. Whatever caused this, fixed itself. Powered up again the next day, problem was gone. So far it has not returned...