Repairing a dead A520 modulator

RiP · 03 July 2018, 10:30

I have just received a dead A520 modulator. There's no sign of fault on its board.
It shows no picture at all. How to fix it?

demolition · 03 July 2018, 10:46

Get a working replacement? There's bound to be plenty out there since hardly anyone is using them nowadays (RGB-SCART looks much better) and most A500 packages included one.

pandy71 · 03 July 2018, 11:17

Use A520 schematics ( http://members.iinet.net.au/~davem2/overclock/A520.html ) and MC1377 datasheet - or replace PCB with something more modern.

Hewitson · 03 July 2018, 12:24

I wouldn't bother fixing it. These things produce the worst picture quality ever.

Daedalus · 03 July 2018, 13:07

Yeah, there has to be a lot of them sitting around unused everywhere since so many people use RGB output these days for its much superior quality. If you really did want to troubleshoot it however, you need to look at the signals with an oscilloscope. Check that the 1377 chip is getting power, then check the clock signals and sync signals are appropriate. No clock signal would suggest looking at the 74 logic ID and/or the crystal on the board. Make sure the RGB signals look ok too, then see if you're getting anything out from the chip's outputs. If you are, you can trace them through the extra analogue stages and see where they stop.

RiP · 06 July 2018, 15:55

1337's power was ok but I don't have oscilloscope =/

03 July 2018, 10:30	#1
RiP Q Join Date: Feb 2017 Location: CD0: Posts: 139	Repairing a dead A520 modulator I have just received a dead A520 modulator. There's no sign of fault on its board. It shows no picture at all. How to fix it?

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03 July 2018, 10:46	#2
demolition Unregistered User Join Date: Sep 2012 Location: Copenhagen / DK Age: 43 Posts: 4,190	Get a working replacement? There's bound to be plenty out there since hardly anyone is using them nowadays (RGB-SCART looks much better) and most A500 packages included one.

03 July 2018, 11:17	#3
pandy71 Registered User Join Date: Jun 2010 Location: PL? Posts: 2,776	Use A520 schematics ( http://members.iinet.net.au/~davem2/overclock/A520.html ) and MC1377 datasheet - or replace PCB with something more modern.

03 July 2018, 12:24	#4
Hewitson Registered User Join Date: Feb 2007 Location: Melbourne, Australia Age: 41 Posts: 3,773	I wouldn't bother fixing it. These things produce the worst picture quality ever.

03 July 2018, 13:07	#5
Daedalus Registered User Join Date: Jun 2009 Location: Dublin, then Glasgow Posts: 6,351	Yeah, there has to be a lot of them sitting around unused everywhere since so many people use RGB output these days for its much superior quality. If you really did want to troubleshoot it however, you need to look at the signals with an oscilloscope. Check that the 1377 chip is getting power, then check the clock signals and sync signals are appropriate. No clock signal would suggest looking at the 74 logic ID and/or the crystal on the board. Make sure the RGB signals look ok too, then see if you're getting anything out from the chip's outputs. If you are, you can trace them through the extra analogue stages and see where they stop.

06 July 2018, 15:55	#6
RiP Q Join Date: Feb 2017 Location: CD0: Posts: 139	1337's power was ok but I don't have oscilloscope =/

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