Problem with Amiga 3000T , Please help !

[Damion]

Hi Anthony,

To look at the maths behind it...
From the RP5C01 datasheet we can see the minimum input voltage is 2.2V at a current of 15µA.  The RTC has a 1.2k Ohm resistor in series with the battery (see schematic).  So it'll develop (1.2k x 15µA) = 18mV, or round to 20mV across it.  So the actual minimum voltage at the RTC becomes (2.2V + 20mV) = 2.22V

Question - is there any harm in removing and bridging that resistor (R179), when replacing the original battery with a diode and 2032 coin? I've done this on my 2000's, by simply installing the diode (1N60 in my case) in place of the resistor (R803). Based on what you've written, it would seem the RTC battery should last quite a bit longer. Any potential issues with this?

Edit: Just pulled my 2000 from the closet, it's been sitting off for well over a year, and the battery is nearing 3 years old. I was surprised to find that it had only lost 20 minutes. Looks like the RTC on the A2000 is good all the way down to 2.0V, which helps.

[nscaleworld]

Well, I checked my stash of zip memory chips and they are indeed mixed.  So, they are most likely mixed in my Amiga 3000T too.  I did not know that there are 2 different types of zip memory and that you are not suppose to mix them.  So, I just spent the last hour sorting thru my pile of zips.  I put all of the SC in one anti-static bag, and all of the FP zips in another.  So, this mixup will never happen again.  Tomorrow, I will remove the Amiga 3000T motherboard from the case.  Then I will remove all of the zip memory and start over.  So, SC zips are best for the 030 processor?
 
I want to thank all of you guys for helping me.  But, I will continue to need your help until I get the old girl back up and running perfectly.  I think correcting the zip memory will fix the disk drive and cpu cashe problem.  I am also going to install the coin battery and hopefully that will fix the problem of Workbench 3.1 not "seeing" the hard drive.
 
Thanks a lot, guys, you are a big help.  :razz:

[Castellen]

Question - is there any harm in removing and bridging that resistor (R179), when replacing the original battery with a diode and 2032 coin? I've done this on my 2000's, by simply installing the diode (1N60 in my case) in place of the resistor (R803). Based on what you've written, it would seem the RTC battery should last quite a bit longer. Any potential issues with this?

The purpose of the resistor in series with the battery is to limit charging current to a safe value when a rechargeable nickel based battery is fitted.  With the lithium cell + diode, the resistor serves no purpose so can be bypassed (short circuit) if you want to, although the gain in battery life in doing so will be miniscule; hardly worth the effort.

As I recall, the 1N60 is a germanium diode so should have forward voltage characteristics comparable to a Schottky diode.  Can't remember the exact specs of them, but put your voltmeter across the diode.  If you see any more than about 0.3V with the computer off, then you can make a worthwhile gain by replacing the 1N60 with a BAT85 or whatever.  

Edit: Just pulled my 2000 from the closet, it's been sitting off for well over a year, and the battery is nearing 3 years old. I was surprised to find that it had only lost 20 minutes. Looks like the RTC on the A2000 is good all the way down to 2.0V, which helps.

The A2000, A500+, A501, etc, use a different RTC device, a Seiko/Epson MSM6242 which does have a lower data retention voltage of 2V as opposed to 2.2V on the Ricoh RP5C01.

Of course it depends on the device and temperature.  While the minimum data retention voltage of 2.0V is the specification, in practice some devices may operate below that.


A little off topic but perhaps worth adding is the fact that the crystal oscillator on the RP5C01 and probably the MSM6242 varies in frequency slightly according to the applied voltage.  I generally calibrate them for f0=32.768kHz at 3.6V (for nickel batteries).  If the voltage drops much below that, the oscillator runs slightly slow.  When the computer is running and the supply voltage is 5V, it runs slightly fast.

And of course as quartz crystals age, they usually drift low in frequency, so that and the lower operating voltage explains your time drift.  Not to mention that those crystals aren't brilliantly accurate over wide temperature ranges.

While you can trim the crystal frequency using the trimming capacitor, you'll need a high impedance input (10M Ohm or better) scope or frequency counter to do it correctly.  Any load on the oscillator circuit from the measuring equipment will change the frequency.

[Matt_H]

Question - is there any harm in removing and bridging that resistor (R179), when replacing the original battery with a diode and 2032 coin? I've done this on my 2000's, by simply installing the diode (1N60 in my case) in place of the resistor (R803). Based on what you've written, it would seem the RTC battery should last quite a bit longer. Any potential issues with this?

Edit: Just pulled my 2000 from the closet, it's been sitting off for well over a year, and the battery is nearing 3 years old. I was surprised to find that it had only lost 20 minutes. Looks like the RTC on the A2000 is good all the way down to 2.0V, which helps.

I think it depends on the battery. The NiMH batteries that I've used seem to lose their charge after a few weeks - much quicker than the NiCd originals.

Well, I checked my stash of zip memory chips and they are indeed mixed.  So, they are most likely mixed in my Amiga 3000T too.  I did not know that there are 2 different types of zip memory and that you are not suppose to mix them.  So, I just spent the last hour sorting thru my pile of zips.  I put all of the SC in one anti-static bag, and all of the FP zips in another.  So, this mixup will never happen again.  Tomorrow, I will remove the Amiga 3000T motherboard from the case.  Then I will remove all of the zip memory and start over.  So, SC zips are best for the 030 processor?

It might be easier to pull the chips with the motherboard in the case, thus providing a strong anchor. You'll definitely want to remove the drive bridge, though, if you haven't already. Well, use your best judgement. And caution.

Also, make sure your ZIPs are all the same size. I'd guess that they are, since Workbench probably reported 16 megs, but since you had some SC/FP mixups, it doesn't hurt to check for a capacity mixup as well

Good luck!

[mechy]

Well he doesnt believe me that the A3000T SCSI NVRam settings are stored on the batt. He doesnt have one installed. This could be a solution.

When the 3000(t) does not have a battery,it falls back to the default scsi settings, worst case it is just not set to synchronous usually. It should still work fine.

[mechy]

6 feet long?! That's way too long. That causes errors, and data loss may occur.
Try shorter cables of 10" - 15" inch max.

That is absolutely wrong, where do you get this stuff. a 6ft cable is fine.

SCSI I standard specifies up to 6 METERS(over 18ft~) for cable length.
SCSI II standard specifies 3 meters which is over 9ft.
 I run long cables in my 3000t's with no issues whatsoever for many years.
Besides,you would be lucky to reach anything in a 3000t with 15" cable.

If anything the revision 4 WD scsi chip is a problem child. Many times you cannot use multiple devices on this and i believe its known to have a broken scsi II command set, it can also be a source of scsi going haywire and giving errors when a A3640 is added into the mix.
Updating to the western digital rev 8 or the Amd chip solves most scsi woes on the 3000.

It might be wise to learn a bit more about scsi instead of putting out bad information on the forums that gets repeated year after year.

Mech

[mechy]

Some good suggestions from Zac67 regarding the memory, certainly worth checking all of the ZIPs are the same.  More information here.





As for the RTC backup power supply; you're far better off using a small signal Schottky diode as opposed to a standard silicon diode (e.g. 1N914, 1N4148, 1N400x, etc).

To look at the maths behind it...
From the RP5C01 datasheet we can see the minimum input voltage is 2.2V at a current of 15µA.  The RTC has a 1.2k Ohm resistor in series with the battery (see schematic).  So it'll develop (1.2k x 15µA) = 18mV, or round to 20mV across it.  So the actual minimum voltage at the RTC becomes (2.2V + 20mV) = 2.22V

If a 1N914 diode was used, we can see it has a forward voltage drop of around 0.55V at 15µA.  So it'll only provide a clock backup until the cell reaches a voltage of (2.22V + 0.55) = 2.77V.  The CR2032 cell is 3V nominal, meaning it only has to discharge by 0.23V to a terminal voltage of 2.77V before it'll need to be replaced, so that's using well under half of the cell's capacity.

If a Schottky diode was used instead, say a common BAT85 for example, we can see the forward voltage drop will be less than 0.24V at 15µA.  So the cell can discharge further to (2.22V + 0.24) = 2.46V before it needs to be replaced.  You still won't get to use the full rated capacity of the cell (230mAHr), but at a guess you'd still get about 60% of that (140mAHr).  At a current draw of 15µA, I'd expect a clock backup time of 389 days or 13 months.  Of course that depends on the exact cell being used, age/condition of the cell, exact current draw of the RTC on standby and the temperature.

So in summary, while the silicon diode will work, you'll get far longer out of the coin cell if you use a small signal Schottky diode.

May i also add the LIR2032 3.6v lithium is a direct replacement for the cr2032 coin cell and is rechargeable,but should NOT be recharged by the amiga,Use the diode as you normally would.Because it starts at 3.6v you will also buy some time before its dead. They make external wall chargers to recharge these coin cells.

[Zac67]

I think it depends on the battery. The NiMH batteries that I've used seem to lose their charge after a few weeks - much quicker than the NiCd originals.

That may be the case with cells optimized for high capacity - self-discharge is ridiculously high. Use long retention cells instead and you're set.

I've got a barrel type NiMH (cheap GP 80 mAh) in my 3k and it lasts ~6 months.

[Damion]

The purpose of the resistor in series with the battery is to limit charging current to a safe value when a rechargeable nickel based battery is fitted.  With the lithium cell + diode, the resistor serves no purpose so can be bypassed (short circuit) if you want to, although the gain in battery life in doing so will be miniscule; hardly worth the effort.

As I recall, the 1N60 is a germanium diode so should have forward voltage characteristics comparable to a Schottky diode.  Can't remember the exact specs of them, but put your voltmeter across the diode.  If you see any more than about 0.3V with the computer off, then you can make a worthwhile gain by replacing the 1N60 with a BAT85 or whatever.  




The A2000, A500+, A501, etc, use a different RTC device, a Seiko/Epson MSM6242 which does have a lower data retention voltage of 2V as opposed to 2.2V on the Ricoh RP5C01.

Of course it depends on the device and temperature.  While the minimum data retention voltage of 2.0V is the specification, in practice some devices may operate below that.


A little off topic but perhaps worth adding is the fact that the crystal oscillator on the RP5C01 and probably the MSM6242 varies in frequency slightly according to the applied voltage.  I generally calibrate them for f0=32.768kHz at 3.6V (for nickel batteries).  If the voltage drops much below that, the oscillator runs slightly slow.  When the computer is running and the supply voltage is 5V, it runs slightly fast.

And of course as quartz crystals age, they usually drift low in frequency, so that and the lower operating voltage explains your time drift.  Not to mention that those crystals aren't brilliantly accurate over wide temperature ranges.

While you can trim the crystal frequency using the trimming capacitor, you'll need a high impedance input (10M Ohm or better) scope or frequency counter to do it correctly.  Any load on the oscillator circuit from the measuring equipment will change the frequency.

Many thanks for the thoughtful reply. Measuring a 0.3V drop here, and 3.05V total on the anode side - looks like it'll go a few more years yet, with the potential to do a bit better with a Schottky.

This is probably obvious, but it's worth mentioning I've had great luck with the Renata (or anything made in Japan) 2032's. The Chinese ones die quickly.

[danbeaver]

I'm confused, is this an A3640 problem (i.e., data cache) or a SCSI controller issue?  I think the battery is well covered. I'm guessing that trying another SCSI controller would help sort out the boot problem

[AmiDude]

That is absolutely wrong, where do you get this stuff. a 6ft cable is fine.

He he... I was mistaken with IDE. Guess I had drunk too much that night. LOL!  :razz: :pint: :crazy:

[magnetic]

Mechy you are right about the rev 4 scsi chip and multiple devices but in this case, I doubt this is the cause of the problems.

And yes 6ft cables are fine for scsi usages as you said

[AmiDude]

Oh and mechy, your post counter is the number of the beast 666. Post a reply or something quickly, before bad things might happen with you... :nervous:  

:razz:

[mousehouse]

Oh and mechy, your post counter is the number of the beast 666. Post a reply or something quickly, before bad things might happen with you... :nervous:  

:razz:

Something bad happened, he's still at that number as we speak!

I found the A3000T to be really nit-picky on jumpers, memory and hard drives. Other than that, when you have it up and running it is the most awesome of all ;-)

It took me some time to get the jumpers right, and not all given settings on the net are right. Also, check if your ZIPs are seated correctly, I've seen them wriggling out over the years. Could also be some ZIP chips are dying, maybe you can take them out easily and run with memory on a different card?

[mechy]

Oh and mechy, your post counter is the number of the beast 666. Post a reply or something quickly, before bad things might happen with you... :nervous:  

:razz:

BOO! hehehe :angryfire:

[mechy]

Many thanks for the thoughtful reply. Measuring a 0.3V drop here, and 3.05V total on the anode side - looks like it'll go a few more years yet, with the potential to do a bit better with a Schottky.

This is probably obvious, but it's worth mentioning I've had great luck with the Renata (or anything made in Japan) 2032's. The Chinese ones die quickly.

No problem with original sony coin cells here, i guess the people having capacity problems are buying those cheap china cells.

Also if there is a bad diode in the circuit or left over leakage from a bad battery that was not cleaned well and can be conductive in some cases.
 it can drain the batteries prematurely.


Mech