Amiga 3000T Low voltage on RTC

[Kawazu]

Hello.
I have just changed the battery on my A3000T to a coincell and im having a bit of a problem.
Pin 18 on 190 is only getting 0.5v

When i messure the voltage on the leggs of the coin cell adapter before i put it into the motherboard i get a nice 2.8v
But when the adapter is placed in its holes on the motherboard and i messure the voltage again i get a 1.73v
And after the R192 resistor it drops to 0.52v

The voltageshould be lower after passing the resistor but why the hell is the voltage dropping from 2.8v to 1.73 on the legs of the adapter when i just place it in its socket?

[Kawazu]

Reminder: Check that you have placed the coincell holder on the adapter pcb the correct way so + goes to + and - to -

[Homer]

It looks like you have already answered your own question :hammer:

[Oldsmobile_Mike]

Any difference with a higher voltage battery?

[Amiwest]

The cell adapter has a reverse voltage protection (diode) that will drop the voltage (.7 volts to .1 volt depending on the diode type. This is required when replacing a chargeable battery with a none chargeable battery.
( battery voltage out of holder should be the 3.6 volts.
To me It looks like c190 could be most likely bad. With the battery out and computer on, pin 18 should be +5, battery in computer and computer off around 2.8 volts

[Castellen]

Hello.
I have just changed the battery on my A3000T to a coincell and im having a bit of a problem.
Pin 18 on 190 is only getting 0.5v

Do you have about 5V on pin 18 of the RTC with the computer powered on?  If so, the RTC and C190/C191 are likely to be OK.

Check that you have about 470 Ohms between the battery + terminal and pin 18 of the RTC, do this without the battery fitted and the computer powered off.

And yes, you'll need a series diode to prevent the lithium cell from charging.  Lift one side of R192 and fit a Schottky diode for lower insertion loss compared to a silicon diode, something like a BAT85 should do the job.

[Homer]

Reminder: Check that you have placed the coincell holder on the adapter pcb the correct way so + goes to + and - to -

I thought that this meant he had realised that the battery holder was the wrong way around on the pcb giving reverse polarity, hence my comment that he had already fixed it.

Kawazu: Did you fix it ? :drink:

[Kawazu]

I thought that this meant he had realised that the battery holder was the wrong way around on the pcb giving reverse polarity, hence my comment that he had already fixed it.

Kawazu: Did you fix it ? :drink:

Yes i did indeed "fix" it
Have 2.8v on pin 18 when the amiga is off and she is keeping the time :roflmao: