Splitting the picture output..

Started by Novabug, 00:20, 09 November 20

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Novabug

Hey everyone, need a little advice.


I made this DIN Splitter below, with the intention of feeding the CPC output into a capture device, while still able to play on the monitor simultaneously. After careful assembly making sure all the correct pins were connected, I conducted a test with one of my (sort of) expendable cpc 464's. Using an unpowered RBG SCART connection (with capacitor mod), I managed to get a picture on both the monitor and the TV. However, the monitor picture was glitchy and the aspect shifted a few MM to one side, and the TV picture had no blue shade. But had other colours.


Unfortunately, after a few minutes playing with the connections, the CPC lost power and won't turn back on. I checked the monitor power supply and it's fine. I have checked the switch in the CPC, it's ok. The power socket is fine also, as are the tracings on the PCB to vital points such as IC/tape deck/expansion pins. Now, have I fried something due to the additional output? If so, what do I need to replace. and also, is there a way to split the signal for the purposes I need if this has fried an IC or component. I'm aware of the power requirements needed for output, but didn't think this would be an issue.


and advice or help would be really appreciated.






Bryce

If the cable really doesn't have any mistakes, then it's highly unlikely that the splitter broke the computer. I used a similar splitter for many years without an issue. I can only assume that something else just happened to fail while you were using it, or while messing about you managed to short something or the electronics got a static discharge. Unfortunately it could be many things that have failed.


Bryce.

Novabug

Making some tests today. The cable is good, I had a clear stable picture when using the monitor, good on both sockets of the split, but the issues started with connecting the TV, which disrupted the picture on the monitor, and then finally stopped. I feared it may be the crtc, but going to do some voltage checks and find out. One thing i did do was change which scart socket i was using on the TV, but i did power down before this.


I wonder if there is any safe way to split the signal for capture purposes.





Bryce

The proper way would be to make a splitter with a driver for each output, but it should work as you built it. Without a driver both pictures would be slightly darker than normal but would still work.

Bryce.

Novabug

So there shouldn't be any hazard from the scart lead, weather active or not?

Bryce

Not if it's correctly wired.

Bryce.

Novabug

Well, good news it's working again after some testing, possible dry solder on the power input. Will try again with an active scart and see if I get a stable output from both viewing devices


vasilisk

Can you provide additional info about this cable? For educational purposes.

Novabug

Sure, here is the basic plan.


However, think stopping any cross-signal is maybe something to add, like a bank of diodes or something.


The CPC I've got back working, appears to now only operate when the DIN is plugged in. Not power at all from the 5v without the DIN in place. Tested monitor with another cpc, powers without DIN. Tried the problem cpc with another monitor, and yes, it needs the DIN in place to power. Odd, never came across this before.




gerald

Quote from: Novabug on 18:12, 09 November 20
Sure, here is the basic plan.


However, think stopping any cross-signal is maybe something to add, like a bank of diodes or something.


The CPC I've got back working, appears to now only operate when the DIN is plugged in. Not power at all from the 5v without the DIN in place. Tested monitor with another cpc, powers without DIN. Tried the problem cpc with another monitor, and yes, it needs the DIN in place to power. Odd, never came across this before.
I would check the power jack  soldering on the CPC. Looks like you lost the GND connection (which then goes through the DIN)

Bryce

Quote from: Novabug on 18:12, 09 November 20
Sure, here is the basic plan.


However, think stopping any cross-signal is maybe something to add, like a bank of diodes or something.


The CPC I've got back working, appears to now only operate when the DIN is plugged in. Not power at all from the 5v without the DIN in place. Tested monitor with another cpc, powers without DIN. Tried the problem cpc with another monitor, and yes, it needs the DIN in place to power. Odd, never came across this before.

Adding diodes will guarantee that you get no picture. Diodes have a voltage drop of about 600mV. The RGB signals are between 0V and 700mV, so only a tiny fraction of the signal would get through.

Bryce.

Novabug

Yeah, of course. They do resist dont they. Connecting another cpc produces a better picture on both TV and monitor, but still have this picture shift to the left on the monitor, unstable image. I'll check the gnd points again, and test with an active scart.

Bryce

Quote from: Novabug on 20:11, 09 November 20
Yeah, of course. They do resist dont they. Connecting another cpc produces a better picture on both TV and monitor, but still have this picture shift to the left on the monitor, unstable image. I'll check the gnd points again, and test with an active scart.

To be pedantic: No, they don't resist, they drop voltage. Resistance is a function of current, ie: the resistance changes depending on the current, whereas diodes drop the same voltage regardless of the current.

Bryce.

Novabug

So, a new issue has arose, and I can't quite get to the bottom of it. The ground on the power jack appears to not work, so while testing the board, i found a break in a tracing near the jack. I repaired it, testing continuity all over the board at vital points, and all seems well. However, it still will only operate when the DIN is plugged into a monitor. So it's grounding on the din i seems. This means I'm unable to use a scart cable to a TV. Has anybody had this issue before and what would be the possible cause when I have checked all the ground points on the pcb.

Chinnery

Quote from: Novabug on 21:06, 22 November 20
So, a new issue has arose, and I can't quite get to the bottom of it. The ground on the power jack appears to not work, so while testing the board, i found a break in a tracing near the jack. I repaired it, testing continuity all over the board at vital points, and all seems well. However, it still will only operate when the DIN is plugged into a monitor. So it's grounding on the din i seems. This means I'm unable to use a scart cable to a TV. Has anybody had this issue before and what would be the possible cause when I have checked all the ground points on the pcb.
It could simply be a dirty or faulty barrel socket. With no power on, can you test the continuity between the outside of the dc jack and gnd in the cpc?

Novabug

The jack socket was new when i originally restored this machine. The trace lines and pads were damaged originally, but continuity is restored, yes.


Novabug

Quote from: gerald on 18:25, 09 November 20
I would check the power jack  soldering on the CPC. Looks like you lost the GND connection (which then goes through the DIN)


Yes, i found a break in the tracing just beyond the jack. However, although I have continuity all over the board now, it still wants to ground on the DIN

Chinnery

Quote from: Novabug on 23:12, 23 November 20
The jack socket was new when i originally restored this machine. The trace lines and pads were damaged originally, but continuity is restored, yes.
Could it be the actual jack? Do you get 5v if you measure the centre to the edge? Does wiggling the wire have any effect? It could be the -ve on the wire that's iffy?

Bryce

Are you sure that BOTH GND pins on the socket are connected? The pin at the back is positive, the other two pins (GND and switched GND) should be connected together to GND.

Bryce.

Novabug

Quote from: Bryce on 14:19, 24 November 20
Are you sure that BOTH GND pins on the socket are connected? The pin at the back is positive, the other two pins (GND and switched GND) should be connected together to GND.

Bryce.


Yes, both the GND are connected together. Here is a video (Which i do for my Patreons) which demonstrates what is happening  with a close up of the PCB. I must be missing something obvious i'm guessing.


https://youtu.be/TPHskCOO7jU

Bryce

At 3:12 in that video you measured between the 5V pin (at the back of the power connector) and the GND pin of the expansion port and got continuity?? Somethings not right there! Just before that you said "Hang on a minute, somethings not right there." You were right, but then you seemed to have got confused and thought it was ok (Spoiler: It wasn't ok). :)


Bryce.





Novabug

Yes, I think I though I was still measuring the GND. With the power switch connected and in the ON position, I get continuity from all GND points from the 5v.... ahhhh.... the solder points on my audio jack mods maybe causing a short, I'll flip the sister board over and check, but other than that, What could this be? Especially since the system operates fine without problems, albeit only with the DIN connected.

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