A600 no composite

[mjnurney]

over the last few months ive had a lot of machines with bad or no composite signal at all - recapping rarely solves or improves the problem one bit.

has anyone found a common fault or reason for this.

I know the BT101 and video DAC may have issues. how do i test them chaps?.

im currently trying a working 600 and comparing it to the bad 600, voltages and contacts.

The RGB works fine as does an A520 on the RGB to achieve composite.

I know the RGB signal is better but some people want composite and hey , it used to work..

mike

 

[roy_bates]

have you had a look to see if the video encoder is actually putting out a compisite signal?

 

[mjnurney]

digging the schematics out as we speak mr VIP

 

[roy_bates]

thank you kind sir,thank you.

 

[sneeker]

I was watching this last night, shows the ghosting and stuff like mind had on composite and how he fixes it.

https://www.youtube.com/watch?v=D8LGfxu2zpI

 

[mjnurney]

@sneeker cheers bud, yes ive seen that and there is a cap and LED mod to achieve the same...

but this has no composite.

anyway what ive found is ...well nothing.

ive checked and changed the caps in the composite line and checked the tracks and all is well , the resistors and FBs all measure properly and i can even hot wire a B/W composite signal from the CXA but still i have no signal at the Comp socket - so as time is against me that will do for today...

until next time!

 

[roy_bates]

try u32.its 74 logic you cant miss it.

 

[jimbob]

Is the RF working? The video signal is shared between RF and composite. Try removing C236 in case a fault in the RF module is somehow causing the composite output to fail.

Also, I think the composite jack has a switch like the audio jacks to switch in a dummy 75ohm load, maybe the switch is faulty.

Not sure why when you hot wire it you get black and white?

 

[TheCorfiot]

Mike, It's the CXA chap, if all voltages going to it are good then its that damn chip again

It can even cause RGB probs too as it is used to buffer the RGB signals from the DAC.

TC

 

[mjnurney]

those damn CXA chips give me some grief...

 

[TheCorfiot]

those damn CXA chips give me some grief...

Yeah, complete and utter ba$tards

TC