Juno first green lines

[Lurch666]

Green lines down the screen and text has jailbars across.
Looking at other repairs it looked like the 4116 ram so I ran @NivagSwerdna test rom but that showed all vram to be OK.
Next I thought it might be the 7489 ram but it wasn't that either. I swapped out the 083 and 083 customs from my hyper sports but that made no difference.
I've checked most of the chips around the 4116 ram but can't see anything wrong except for a damaged track coming from pin 11 of the LS367 at F11.


It doesn't appear to affect the bad graphics and even with F12 removed from the the game appears to run fine so that's not the issue.

So any ideas where else I could look.

 

[NivagSwerdna]

Did the roms all pass their checksums?

It's hard to know if the frame buffer is not being populated properly or not rendered properly

 

[Lurch666]

All except for the one at A10.
While the jailbars though the text may have something to do with the 4116 ram I'm thinking the green lines are something else since if a 4116 ram is bad the lines are horizontal (if the monitor is set to it's normal vertical orientation) where the green lines are vertical.

 

[big10p]

Does all video ram look original? Is it in spec (i.e. fast enough)?

 

[Lurch666]

The 4116? All original. None of it socketed.

 

[Lurch666]

Just tried the test rom again and saw something I missed.
The green lines appear to change as the test goes on but not in a consistent manner and disappear during the sound test for a while.
Didn't notice this during the gameplay as there's a lot going on so the test rom has helped me spot this.
I don't now think it's a ram issue as the lines are broken in a very consistent way so it's possibly some timing signal being off.

 

[big10p]

Sure looks like the green lines are associated with the text layer. But then the sprite going along the bottom seems to cause a line to show. Maybe a fault in the section that combines layers? Just a guess as I'm still very much a noob at this stuff.

 

[Retroman839]

All except for the one at A10.
While the jailbars though the text may have something to do with the 4116 ram I'm thinking the green lines are something else since if a 4116 ram is bad the lines are horizontal (if the monitor is set to it's normal vertical orientation) where the green lines are vertical.

are you getting good voltage for the 4116 ?

• Shift Register/Logic Chips: ICs responsible for serializing pixel data (e.g., 74166, 74165) often fail with distinct vertical lines during display or RAM test routines. [1]

• Multiplexers & Buffers: Components like 74LS257 or data buffers (74LS374) that route address lines to the video RAM

 

[Retroman839]

4116 rule out if games running as for cpu ram.

If the vertical lines appear everywhere on the screen and affect the text/writingwhile the game is running, you can rule out the 4116 main CPU RAM.
This behavior means the main CPU is functioning properly—it is computing game logic and actively writing data to the video layout. The issue lies entirely in the final stages of the video generation path, where character text and background elements are serialized into pixels.
On a Konami Juno First board, check these components in order:

1. The Character RAM (Most Likely)
Juno First handles screen text (scores, lives, waves) through a dedicated pair of 2114 Static RAM chips located on the video board.

• The Fault: If one of these RAM chips has a failed internal data pin, it cannot hold stable bits for character generation. This injects constant vertical stripes directly through the text and background grid.

2114 fails
It fails to hold the characters in that
Position .. displaying random vertical lines

 

[Retroman839]

Similair to where I was with my Bombjack after rulling out the rams .

Start digging round the 74ls’s maybe
Piggy back 2114 sram

 

[Lurch666]

CPU ram isn't 4116 it's 2128 and there are no 2114 rams on this PCB.

 

[Lurch666]

With my video probe I've found the green lines are coming from pin 13 of the 373 at E14.
When I video probe it there's solid green lines exactly where the broken green lines appear so the errant data is being mixed into DB6 somewhere.

 

[Retroman839]

CPU ram isn't 4116 it's 2128 and there are no 2114 rams on this PCB.

So much for AI !

 

[Retroman839]

Is The principle sound ?

That the issue is in the final video genaration stage .

A 74ls stuck ?

a shift register has a corrupt bit and repeating it forming the lines ?

Its drawing but drawing garbage

 

[NivagSwerdna]

The video is quite interesting...

Firstly the JUNO FIRST and the space ship along the bottom are painted by the blitter hardware... and that looks fine.

On Page 1...

STATIC OK has some bits missing and they seem to have been painted repetively elsewhere but in the wrong direction...

On Page 2...
As the checksums are rendered the more green lines occur...
When the 2nd column is painted... more green lines...
There are definitely bits missing from the checksums that then manifest themselves as green lines...
Again the blitter ship works fine until right at the end.. an extra green line... weird!

On Page 3...
You get a green line and then it disappears (as a side effect of the SFX numbering)
It comes back at SFX 08.... and interestingly the blitted ship causes a green line to appear and disappear!

Let's not blame the Konami 081 for the moment.. the interleaved DRAM timing is a nightmare...

I would be tempted to socket and swap the 74LS153s around that mux the addresses...


weird that the VRAM test works... I'm not really sure TBH

 

[NivagSwerdna]

correction... so there are artifacts on the blitted Juno First...


From MAME but probably not far off

 

[NivagSwerdna]

Does the game play fine? i.e. it is just the rendering that is the problem?
I guess logically if the VRAM test passes then it must just be the VRAM to video logic?
But it dependent on the value in the VRAM... tough one. This is what we come to school for...! Good Luck!

 

[NivagSwerdna]

We must be able to deduce something from this

 

[Retroman839]

Vertical seems to have some incorrect info in the center lines of the drawn characters also

 

[Retroman839]

Try probing outputs of the inputs
On the 74ls166 ( if it has one of these chips ) or 74LS157/74LS257

as the screen matrix is x axis horizontal as it follows the monitors raster
Faulty selecter pin on the mux
Causing it to lock up over laying in
Straight lines ..

This one maybe be intermittently locking up ( shorting internally )