Amiga 600 one color going funky on composite

Bren McGuire · 27 May 2022, 16:50

I have actually two A600s doing the same thing, one color (I think blue?) is flashing and being weird all over in Composite video, but everything is fine via RGB. One machine does it worse than the other, to the point that it is unwatchable via composite.
Seems like the issue gets more noticeable on PCMCIA read access on the machine doing it less.

Is this a capacitor problem or a video encoder chip problem?

MrClump · 30 May 2022, 17:42

That two Amigas are doing the same makes me sceptical the issue is with the Amiga and is something display related?

If it is fine via RGB that rules out quite a lot, so my hunch would be that whipping out U12, Z221 and Z222 and completing the mod below will likely fix it.

https://www.ikod.se/cxa2075m/

Every A600 with composite issues that I have come across has been fixed by the above mod.

What do you get from the RF modulator, as the same composite signal is feeding into that.

Have both Amigas been recapped? There are a lot of caps in that area of the board to leak and cause damage to the display circuitry.

Amiga1992 · 31 May 2022, 16:25

I've had this issue with A600s before too, especially the "disk access causes flicker" bit.
On recapped Amigas no less. Tested on different displays. Not a display issue.

Bren McGuire · 21 June 2022, 02:27

They're both recapped and they do this in several displays, it isnt the display

Quote:

Originally Posted by MrClump

Have both Amigas been recapped? There are a lot of caps in that area of the board to leak and cause damage to the display circuitry.

MrClump · 21 June 2022, 08:11

How does the RF output look, as the composite video signal is fed into that on it's way to the composite socket.

A10001986 · 21 June 2022, 08:34

Is C459 an electrolytic cap?

MrClump · 21 June 2022, 17:53

Quote:

Originally Posted by A10001986

Is C459 an electrolytic cap?

Yes

alexh · 22 June 2022, 09:56

Quote:

Originally Posted by Bren McGuire

I have actually two A600s doing the same thing, one color (I think blue?) is flashing and being weird all over in Composite video, but everything is fine via RGB. One machine does it worse than the other, to the point that it is unwatchable via composite.
Seems like the issue gets more noticeable on PCMCIA read access on the machine doing it less.

Is this a capacitor problem or a video encoder chip problem?

This happens on my A600 if the PCMCIA port is active. My A600 is not recapped. I was thinking it was probably a design fault on this revision motherboard.

Bren McGuire · 22 June 2022, 18:13

could it just be a faulty video decoder?

MrClump · 22 June 2022, 18:16

Quote:

Originally Posted by alexh

This happens on my A600 if the PCMCIA port is active. My A600 is not recapped. I was thinking it was probably a design fault on this revision motherboard.

If your A600 has not been recapped then I would say all bets are off. The area close to the PCMCIA socket is packed with capacitors that are prone to leaking and also a lot of display circuitry.

MrClump · 22 June 2022, 18:32

Quote:

Originally Posted by Bren McGuire

could it just be a faulty video decoder?

Potentially, which is why I am asking about the RF output.

Cobe · 22 June 2022, 22:59

This happens on my 1200 too.

alexh · 23 June 2022, 14:55

Quote:

Originally Posted by MrClump

If your A600 has not been recapped then I would say all bets are off. The area close to the PCMCIA socket is packed with capacitors that are prone to leaking and also a lot of display circuitry.

They have not leaked. The pads of all caps are nice a shiny. There is no need to replace them "because".

I am aware that capacitors can go bad. However I imagine far more boards have been killed by amateurs with no soldering skills who have attempted to replace SMT caps, having been told to "replace them before they go bad".

Bren McGuire · 20 July 2022, 16:05

if the capacitors are leaky they are too far gone. however i know they act up and go bad way before the leak, so that is not a sign that your board is fine.
if you notice any such issues, is possible your caps are already bad.
basically if your caps are more than 10 years old, they are bad. sure, amateurs wrecking amigas are no good, but you can always take it to a professional

its not scaremongering, these capacitors truly are bad and go bad after about ten years. i would recommend you to recap. it's no "because", it is known problem,. amiga is not the only platform with this issue.

Quote:

Originally Posted by alexh

They have not leaked. The pads of all caps are nice a shiny. There is no need to replace them "because".

27 May 2022, 16:50	#1
Bren McGuire Registered User Join Date: Nov 2019 Location: Croydon Posts: 580	Amiga 600 one color going funky on composite I have actually two A600s doing the same thing, one color (I think blue?) is flashing and being weird all over in Composite video, but everything is fine via RGB. One machine does it worse than the other, to the point that it is unwatchable via composite. Seems like the issue gets more noticeable on PCMCIA read access on the machine doing it less. Is this a capacitor problem or a video encoder chip problem?

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Composite Video in color mode	TymoDEV	support.Hardware	10	26 February 2021 00:54
Amiga 600 vs Amiga 1200 Composite Output Quality	Marle	support.Hardware	2	22 March 2020 23:20
Monochrome video out vs Composite color burst options	mark_k	support.WinUAE	6	25 February 2019 20:04
A600 color bands on composite problem	Amiga1992	support.Hardware	6	24 October 2013 13:58
Amiga 600 B/W on Composite	mstjohn1974	support.Hardware	7	19 June 2008 21:17

30 May 2022, 17:42	#2
MrClump Registered User Join Date: Aug 2020 Location: Torquay Posts: 166	That two Amigas are doing the same makes me sceptical the issue is with the Amiga and is something display related? If it is fine via RGB that rules out quite a lot, so my hunch would be that whipping out U12, Z221 and Z222 and completing the mod below will likely fix it. https://www.ikod.se/cxa2075m/ Every A600 with composite issues that I have come across has been fixed by the above mod. What do you get from the RF modulator, as the same composite signal is feeding into that. Have both Amigas been recapped? There are a lot of caps in that area of the board to leak and cause damage to the display circuitry.

31 May 2022, 16:25	#3
Amiga1992 Registered User Join Date: May 2001 Location: ? Posts: 19,645	I've had this issue with A600s before too, especially the "disk access causes flicker" bit. On recapped Amigas no less. Tested on different displays. Not a display issue.

21 June 2022, 08:11	#5
MrClump Registered User Join Date: Aug 2020 Location: Torquay Posts: 166	How does the RF output look, as the composite video signal is fed into that on it's way to the composite socket.

21 June 2022, 08:34	#6
A10001986 Registered User Join Date: Jun 2017 Location: 1986 Posts: 79	Is C459 an electrolytic cap?

22 June 2022, 18:13	#9
Bren McGuire Registered User Join Date: Nov 2019 Location: Croydon Posts: 580	could it just be a faulty video decoder?

22 June 2022, 22:59	#12
Cobe Registered User Join Date: Jan 2014 Location: Belgrade / Serbia Age: 41 Posts: 1,004	This happens on my 1200 too.

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)