STE video synchronisation problem

[exxos]

I see it, but it's very unstable and jerky. Is it fairly stable on your machine?

It's not great no. Though the scope will be loading the signal and causing some issues anyway.

So I think your input to pin 17 is just fine by the looks for it. ..


As for pin 9, I see this... again with 100mV/DIV X10 probe.

c4.png

[Number_Nine]

I see it, but it's very unstable and jerky. Is it fairly stable on your machine?

It's not great no. Though the scope will be loading the signal and causing some issues anyway.

So I think your input to pin 17 is just fine by the looks for it. ..


As for pin 9, I see this... again with 100mV/DIV X10 probe.


c4.png

Yeah, so you see composite PAL signal (with colours from pins 3,4,5 added onto composite sync after colour burst), and on pin 2 you'll see only composite sync of the same form, but without colours.
On my machine I see this on pin 2 (correct form):

SDS00007.jpg

But only this on pin 9:

SDS00008.jpg

[exxos]

But only this on pin 9:
SDS00008.jpg

are you using x10 probe and 100mV/DIV on your scope ? If so , try 10mV and see if you can see anything..

I also assume you have pin 9 still bent upwards out of the socket ?

[Number_Nine]

It's not great no. Though the scope will be loading the signal and causing some issues anyway.

So I think your input to pin 17 is just fine by the looks for it. ..


As for pin 9, I see this... again with 100mV/DIV X10 probe.


c4.png

Yeah, so you see composite PAL signal (with colours from pins 3,4,5 added onto composite sync after colour burst), and on pin 2 you'll see only composite sync of the same form, but without colours.
On my machine I see this on pin 2 (correct form):
SDS00007.jpg

But only this on pin 9:
SDS00008.jpg

It looks a bit like an audio signal, maybe it's trying to say something:

SDS00009.jpg

[Number_Nine]

Yeah, so you see composite PAL signal (with colours from pins 3,4,5 added onto composite sync after colour burst), and on pin 2 you'll see only composite sync of the same form, but without colours.
On my machine I see this on pin 2 (correct form):
SDS00007.jpg

But only this on pin 9:
SDS00008.jpg

It looks a bit like an audio signal, maybe it's trying to say something:
SDS00009.jpg

Jokes aside, with the same time frame as your picture:

SDS00011.jpg

[exxos]

Hold up..

SDS00008.jpg

If that is 6.7V there, then the IC is getting a external DC bias somewhere. Like Q404 C-B short.. feeding 12V into 1377 pin 9...

I think you need to try one of the IC's like you are using now in your working ST and see if you have composite there..

I have a feeling now that every IC you put in your faulty machine is getting blown up by something around Q404... you need to see if such 1377 works in your known working ST...

If the IC does not work, then you know what the problem is... then you will need to try a known good 1377 in your faulty machine, but lift pin 9 before powering up.. and re-check the output..

[Number_Nine]

It looks a bit like an audio signal, maybe it's trying to say something:
SDS00009.jpg

Jokes aside, with the same time frame as your picture:
SDS00011.jpg

Same with pin 9 upwards:

SDS00001.jpg

[Number_Nine]

Hold up..


SDS00008.jpg


If that is 6.7V there, then the IC is getting a external DC bias somewhere. Like Q404 C-B short.. feeding 12V into 1377 pin 9...

I think you need to try one of the IC's like you are using now in your working ST and see if you have composite there..

I have a feeling now that every IC you put in your faulty machine is getting blown up by something around Q404... you need to see if such 1377 works in your known working ST...

If the IC does not work, then you know what the problem is... then you will need to try a known good 1377 in your faulty machine, but lift pin 9 before powering up.. and re-check the output..

I thought that too and have even bought more MC1377s, but then if I'd just measure pin 9 on socket without the IC, then I should have seen something like >5-6VDC, but I see only this:

SDS00002.jpg

[exxos]

I thought that too and have even bought more MC1377s, but if I just measure pin 9 on socket without the IC, then I should see something like >5-6VDC, but I see only this:

I would confirm your IC's are "blown" on your other machine before anything else..

or try a brand new IC (never before being used) and lift pin 9 and re-check..

I suspect every IC you are putting in that faulty STE is blowing your 1377's up.

You clearly have all the inputs as I do, but no outputs, so , IC faulty or something is blowing the IC up, IE, CB short on Q404.

So if you make sure you lift pin 9, or remove R442... and try a new never before used IC... and see what happens...

[Number_Nine]

I thought that too and have even bought more MC1377s, but if I just measure pin 9 on socket without the IC, then I should see something like >5-6VDC, but I see only this:

I would confirm your IC's are "blown" on your other machine before anything else..

or try a brand new IC (never before being used) and lift pin 9 and re-check..

I suspect every IC you are putting in that faulty STE is blowing your 1377's up.

You clearly have all the inputs as I do, but no outputs, so , IC faulty or something is blowing the IC up, IE, CB short on Q404.

So if you make sure you lift pin 9, or remove R442... and try a new never before used IC... and see what happens...

I've ordered some more Chinese 1377, let's wait for them to have delivered, honestly I don't want to experiment much with my good Atari as I want at least one good Atari STE at home ;)

My current theory is that just these 1377 off ebay were all dodgy, although it's unlikely as their pins looked never soldered, so your theory definitely fits better.