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VK2MCT
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Joined: 30/03/2012
Location: Australia
Posts: 120

Posted: 11:27pm 22 Mar 2018

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Hi,
I'm 'finishing' an Altronics Colour Maximite.
It doesn't work when power is applied, but starts very reliably when reset pin taken low.
I am running an external power supply and failure also occurs using USB power.
Failure also occurs when power is interrupted using the board power connector.
125ma is drawn when first powered up (and not working) as well as when reset (and working).
VCAP is as supplied, 10uf ceramic SMD.
Any thoughts before I replace VCAP (with higher value). It's in a difficult board location.
Thanks,
John B

TassyJim

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Joined: 07/08/2011
Location: Australia
Posts: 6283

Posted: 01:33am 23 Mar 2018

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Does the power LED come on when the Maximite is in fault mode?
The LED is controlled from one of the IO pins.

I would take the opportunity to update the firmware to the latest version while you have the chance.

Rather than replace the VCAP, can you add another one in parallel?
It might be easier than removing the old one.

Do you have a SD card installed?
If it's drawing too much from the 3.3V, it might cause a slow voltage rise on startup.

Jim

VK7JH
MMedit

VK2MCT
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Joined: 30/03/2012
Location: Australia
Posts: 120

Posted: 03:31am 23 Mar 2018

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Thanks Jim,
I had incorrectly assumed that the LED was conn to the supply. It's on in the fault mode.
Just observed that if I power up with VGA conn it fails BUT if I power up with the VGA 9pin disconnected and then connect the VGA then all is good.
I thinking that the problem is a very quirky display or something weird with the VGA/composite detection. (via the 9Pin).
Hmm?
John.

TassyJim

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Joined: 07/08/2011
Location: Australia
Posts: 6283

Posted: 04:01am 23 Mar 2018

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VK2MCT said
I thinking that the problem is a very quirky display or something weird with the VGA/composite detection. (via the 9Pin).
Hmm?
John.

That could be right.
I have a very dim memory of some monitors doing strange things with pin 9 and getting the Maximite confused.
The memory is VERY dim.

If you are not likely to use composite output, cut the trace to VGA pin 9. I think you can safely leave it floating.

It is good to see some colour and mono Maximites fighting back.

Jim

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VK2MCT
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Joined: 30/03/2012
Location: Australia
Posts: 120

Posted: 04:15am 23 Mar 2018

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Currently running V4.0. Manual says Config can change PAL/NTSC
and VIDEO OFF (whatever that means).
As you suggest an install to V4.5 would be a good thing to do & this ver allows turning off composite and detection as well.
Have looked at the change log and there is so much goodness added between V4.0 & V4.5.
Thanks for your help.
John.

flip
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Joined: 18/07/2016
Location: Australia
Posts: 114

Posted: 04:16am 23 Mar 2018

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Hi John, You may already have it sorted, but in case not some thoughts

1. Could it be the reset pin is floating?
The CMM circuit I have shows 10k resistor to +3.3V and no cap on the reset pin

Maybe try checking solder joints/voltages at the reset(MCLR) pin...even clipping in a 10uF cap between MCLR(+ve) to GND(though it shouldn't be needed)

2.The VCAP has been discussed before on this forum...47uF has been suggested (esp.if higher voltage) ...but this would point to a different cause

3.Other than that your supply voltage may be struggling..check Power supply caps can carry the transient current without sagging (again clip a larger say 100uF cap across supply)?

These are just guesses though and you may have thought of these already...
Regards,
PhilEdited by flip 2018-03-24

palcal

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Joined: 12/10/2011
Location: Australia
Posts: 1993

Posted: 09:22pm 23 Mar 2018

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Is this any help HERE

Paul.

edit.... it's now Pg. 16Edited by palcal 2018-03-25

"It is better to be ignorant and ask a stupid question than to be plain Stupid and not ask at all"

VK2MCT
Senior Member

Joined: 30/03/2012
Location: Australia
Posts: 120

Posted: 03:23am 24 Mar 2018

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Hi Jim,
Upgrade to V4.5c solved the problem, no track cuts needed.
Thanks for you help.

Phil, the clue that the 'power' led was on in both OK and not OK conditions, was a really good clue to me that the CPU was running even though there wasn't a VGA display.
Thus that my initial thought there was an issue with VCAP was incorrect.

Paul, thanks, I hadn't known about the watchdog stuff for brownouts. Or is that browndog stuff for watches.

Thank You All.

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