Electrohome G02 Garbled Picture

[lostboy4480]

I just acquired an old cab with an Electrohome G02 in it.

I have just hooked it up to see what state it's in and to my surprise it powers on.  So I quickly hooked up a board to it to see how it looks and this is what I get,  I have tried another know working board and get the exact same garbled picture. It's not rolling or jumping around.

Could someone point me in the right direction as to what to look at next.

Thank you

[Paradroid]

Does that thing have H-Sync and V-Sync adjustment pots? I'd be fiddling with them first up... looks like a sync issue to me.

[qrz]

slanted to the left , Hosc too low of reference signal

i assume it to be be rolling vertically ...?
(can't see that in a still pic)

if such, check sync connection - as no sync lock

[lostboy4480]

Thanks for the ideas,

The monitor does have a V Sync pot and by adjusting that I can stop the rolling but the picture stays the same..

The monitor has separate V Sync and H Sync inputs but the jamma only has a single sync.. Should I split this to both sync inputs.

Once again thank you.

[qrz]

will assume it uses composite sync. so, yes connect to both.


while the Hosc is currently free running, it is a good opportunity to adjust the frequency (Hhold)
turn the ctl slightly until the lines become vert or slant just to the right .

[lostboy4480]

Thank you qrz,

From reading the manual, I believe this is what your talking about.

4. Horizontal Oscillator Adjustment
If there is difficulty in maintaining horizontal sync short out the sync pulse at C901 to ground.  Adjust horizontal oscillator coil L901 until raster is a close to sync as possible.

My question is, does it mater what side of C901 I pull to ground ?

Sorry for all the questions, I am trying to learn

[qrz]

don't really need to so do .
not connecting the sync has the same effect AND easier   

[mgb]

not sure if i missed it but did you try jumping both the v and h syncs together so that your jamma composite sync terminates to both at the monitor?

[lostboy4480]

I guess I should have paid a little more attention to the manual..

So it looks like my G02 needs positive sync,  I had been trying to test with a few different Jamma boards that are all Negative sync..

What is the easiest way to convert the negative sync output to positive sync...

I believe I would need the opposite of something like this
http://www.twobits.com/RGB/cga.gif

[lostboy4480]

So the sync can be inverted with a 74ls04



I might try building a self powered one like this, as this one device should support everything I might need, positive > Negative and vice versa, and separate to composite sync..



Is there anything I might be missing, (I realize the diodes on the power lines are back to front in this diagram)