Looks like it's A500 at fault (Help)

[razz177]

Continuing My pink screen fault, Eventually plucked up courage to mess with wires in scart plug, continuity on all wires is there, stripped scart open plugged in sync /Red / Blue / fine plugged in Green makes no difference , If I plug red or blue into green socket I get the green.

I do not know what to check next If you could help me that would be great, make it nice and simple as I am just trying to learn all this (retirement projects).
I do have a Multi-meter.
I bet I am taking the motherboard out again.
Thanks for your help
Raymond

[a1exh]

I would check continuity from outside on the GREEN PIN of the video connector to inside the case where it is soldered to the PCB. Look for a dry solder joint. Lots of plugging and unplugging might have made it loose?

If good, trace the green signal all the way back to the VIDC checking continuity.

The A310 had two FCO's associated with the analog video output. Depending how long it was kept in service perhaps the A500 had similar ones?

Read the FCO's and see if you can find similar modifications between the VIDC and the Video Output connector on your A500?

https://www.4corn.co.uk/archive//acornf ... coe009.txt
https://www.4corn.co.uk/archive//acornf ... coe011.txt

SoG (Sync on Green) was common on many monitors but not so much on TVs. FCO 9 is a modification you could do to an A310 to remove SoG and improve output levels. Perhaps a similar modification has been made to your A500? Maybe it has gone bad? Look around for bodge wires, missing resistors etc. between the VIDC and the video output connector.

[SKS1]

Remember VIDC1 in A500 != VIDC2 in production systems, different analogue video circuit. A500 is likely to be more similar to the A500_2p circuit I linked to.

I see from your earlier thread "I did get a good picture for a while after cleaning keyboard and before I refitted it's case, then back to pink." suggests a dry joint on the board to me.

[paulb]

Remember VIDC1 in A500 != VIDC2 in production systems, different analogue video circuit. A500 is likely to be more similar to the A500_2p circuit I linked to.

According to the VIDC datasheet, VIDC1 and VIDC2 differ in terms of video output level handling and audio output bit ordering. I guess that the different "sense" of the video output is the key differentiator here.

[razz177]

I would check continuity from outside on the GREEN PIN of the video connector to inside the case where it is soldered to the PCB. Look for a dry solder joint. Lots of plugging and unplugging might have made it loose?

If good, trace the green signal all the way back to the VIDC checking continuity.

The A310 had two FCO's associated with the analog video output. Depending how long it was kept in service perhaps the A500 had similar ones?

Read the FCO's and see if you can find similar modifications between the VIDC and the Video Output connector on your A500?

https://www.4corn.co.uk/archive//acornf ... coe009.txt
https://www.4corn.co.uk/archive//acornf ... coe011.txt

SoG (Sync on Green) was common on many monitors but not so much on TVs. FCO 9 is a modification you could do to an A310 to remove SoG and improve output levels. Perhaps a similar modification has been made to your A500? Maybe it has gone bad? Look around for bodge wires, missing resistors etc. between the VIDC and the video output connector.

Hi
Just been having a look at this, I left the lead plugged into the computer continuity still there upto the resisters R32,R35,R38, I do not know where they go from here.
I removed these the 3.jpg one from each of these, there is a right spaghetti junction just behind these but what it all is I do not know.
The document fcoe011.txt does not seem to match my PCB unless I am seeing it wrong (that is possible)
All in All I have had this looking as it should correct picture.jpg, I have looked around and connot see any bad connections but a trained eye might see what I cannot.
I will attach some pictures.
Thanks for you help

[razz177]

Remember VIDC1 in A500 != VIDC2 in production systems, different analogue video circuit. A500 is likely to be more similar to the A500_2p circuit I linked to.

I see from your earlier thread "I did get a good picture for a while after cleaning keyboard and before I refitted it's case, then back to pink." suggests a dry joint on the board to me.

I have downloaded the document but it is not very clear to me I will have a look with fresh eyes in the morning.
Thank You

[steve3000]

The 2nd photo isn’t the clearest but on the underside of the pcb it looks like there’s a black wire tapping into the video signals, can you take a clear close-up of this? Any idea what this is for, and is it cleanly soldered - no breaks in the black insulation up to the joint, and not accidentally bridging anything?

When looking for a dry joint, I’d suggest looking carefully around the pins of the RGB socket, and try waggling the socket while looking at the solder around its pins on the underside of the pcb - if you do have a dry joint there, you may see the pin or solder moves (which it shouldn’t).

[a1exh]

The latest picture of the screen shows there's no missing green. If there was the acorn would be black. I think it's red that's over saturated. Maybe you need an inline resistor on red you could add it in the SCART hood?

[razz177]

The latest picture of the screen shows there's no missing green. If there was the acorn would be black. I think it's red that's over saturated. Maybe you need an inline resistor on red you could add it in the SCART hood?

The picture was pink then while I was cleaning out the keyboard it turned to normal as in the picture before turning back to pink.
As it stands now I have removed all the cables from the scart plug and plugged them in individually If I plug the green cable where it should go I get thin very pale green vertical lines. if I plug the red or blue cable in the green place I get green as it should be there is continuity right back to some resistors inside the computer.

[razz177]

The 2nd photo isn’t the clearest but on the underside of the pcb it looks like there’s a black wire tapping into the video signals, can you take a clear close-up of this? Any idea what this is for, and is it cleanly soldered - no breaks in the black insulation up to the joint, and not accidentally bridging anything?

When looking for a dry joint, I’d suggest looking carefully around the pins of the RGB socket, and try waggling the socket while looking at the solder around its pins on the underside of the pcb - if you do have a dry joint there, you may see the pin or solder moves (which it shouldn’t).

The black wire goes from LK10 pin 3 to TR11 pin1 as I see LK10 it is east pin 2-3 the yellow wire goes to LK10 pin 2, \i think LK10 as been fitted after production as there is no solder pad where the black wire is soldered but it seems a good joint without breaks could this be to do with getting video out of BNC
According to service manual LK10 is not used.

[SKS1]

According to service manual LK10 is not used.

There is no service manual for A500 that I am aware of. You may be referring to the Archimedes A500 series one, which is for the later A540?

Having just said that, of course I then find the A500 Hardwarde Guide on the CCH site: https://www.computinghistory.org.uk/det ... corn-A500/

[razz177]

According to service manual LK10 is not used.

There is no service manual for A500 that I am aware of. You may be referring to the Archimedes A500 series one, which is for the later A540?

Having just said that, of course I then find the A500 Hardwarde Guide on the CCH site: https://www.computinghistory.org.uk/det ... corn-A500/

Yes that is what I was looking at, and then I found this A500R200SM link settings.pdf
I am now working upto just re-flowing everthing around that area

[SKS1]

According to service manual LK10 is not used.

There is no service manual for A500 that I am aware of. You may be referring to the Archimedes A500 series one, which is for the later A540?

Having just said that, of course I then find the A500 Hardwarde Guide on the CCH site: https://www.computinghistory.org.uk/det ... corn-A500/

Yes that is what I was looking at, and then I found this A500R200SM link settings.pdf
I am now working upto just re-flowing everthing around that area

A500R200SM link settings is for the later A540/R260

I am now working upto just re-flowing everthing around that area.

Yeah. given that you have seen it working intermittently, not too bad an idea.

[a1exh]

Just reflowing the video socket might be enough?

[razz177]

When I first got this problem I thought maybe loose wire in scart or din plug, when I opened them there were no resistors or anything else but I could not believe the scart plug wiring.
Scart plug.jpg

The white wire is not connected to anything but it connected to pin 6 (center) pin on the din plug.