Outrun - No video

I think you just lost sync and your monitor will not come on line with out it. No software exists to check this. You need O Scope to look at sync out of video out. Simple repair if this is so.
Thank you. I don't have an o-scope but very fortunately I live pretty close to @parism and he has graciously agreed to take a look at it for me.
 
OK, so @irepairsega's comment about losing sync got me thinking and I decided to dig in a little more. Research here on KLOV led me to looking at IC91 (74LS125 buffer IC) and IC106 (the big custom) on the video board. I saw several other posts about similar problems that pointed to IC91 failing.

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I was able to use my good Outrun Turbo conversion board as a baseline test since that was working. I attached pin grabbers to pins 5 & 6 of IC91 which are the A2/Y2 pair according to the datasheet. Pin 5 is the incoming composite sync signal from IC106, and Pin 6 is the output from IC91 to the video connector. I then put the CPU board back on the stack and powered the game up. Video was fine (this is the board set that works, so no surprise).

IMG_2617.jpeg

First thing I did was try my logic probe on the video connector's pins, with the following results:
Pin 5 (video ground) ==> LOW - duh
Pins 1, 2, 3 (R, G, and B) ==> "data" patterns - high speed irregular tone variations.
Pin 4 (Sync) ==> A very regular pattern. A high pitched squeal with a periodic pause. I would be pretty sure I was hearing a representation of the horizontal sweep and the periodic vertical blanking.

I moved the logic probe to IC91 pin 6 (sync output) and the pattern sounded the same, and also on IC91 pin 5 (sync input from IC106) and it also sounded the same. I then decided to try the $30 pocket oscilloscope I grabbed from Amazon (who knew you could get a basic o-scope for $30? I had no idea!). The video connector (and IC91 pin 6) both showed this:

IMG_2618.jpeg
3.3v RMS and 2.9Vpp (seems consistent with my understanding of typical monitor voltage levels) and a 15.438KHz frequency. You can see the periodic dropout for the vertical blanking.

I moved my probe to IC91 pin 5, and saw this:

IMG_2619.jpeg

Similar frequency and cycle time, higher voltage. I guess the IC106 chip operates at a higher voltage level and IC91 knocks that down to monitor signal voltage levels, and inverts it as well I believe.

OK, so now I moved my probes to the same locations on the problem Outrun video board. My logic probe gave me different results:

Pin 5 (video gnd) ==> LOW (again, duh)
Pins 1-3 (RGB) ==> Data sounds (OK)
Pin 4 (Sync) ==> STUCK HIGH!!!

Sync was not pulsing, it was just stuck on a constant high signal. I moved the probe to IC91 Pin 6 (sync output) and it also read HIGH with no pulsing. Then I moved it to IC91 Pin 5 (the sync input coming from IC106) — and it was the regular pulsing pattern just like I heard on the good board! A ha! This points to IC91 being bad.

I also viewed the signal on the oscilloscope again. Here's the Sync signal from the video connector and also from IC91 Pin 6:

IMG_2624.jpeg
No pattern indicating periodic vertical blanking, and the frequency was reading 270KHz. Voltage was a fixed 3.6v, nothing to indicate pulses or a pattern of any kind.

Moved the o-scope probe to IC91 Pin 5 (the incoming sync from IC106), and it looked identical to the pattern from the good Outrun Turbo board:

IMG_2627.jpeg
Very, very similar values to the known good Outrun Turbo board.

Conclusions:
IC106 (the big custom chip) is good, as it's outputting a good sync signal just like the one on the known good board
IC91 (74LS125) seems to have failed, it has correct signal input on A2/Pin 5, but the output on Y2/Pin 6 is stuck HIGH and is not providing a 15KHz signal.

Plan:
Remove IC91, install a socket and a new equivalent replacement.

I have already ordered some 14 pin sockets and replacement 74LS125s (TI SN74LS125ANs specifically) from Mouser, and they will be here in a few days.

Will update in a few days. If I replace IC91 and still have a problem, then I will take it to see @parism, but I'm feeling pretty confident I found the culprit. And I learned a bunch about tracing the video signal and using an oscilloscope too!
 

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HOLY SHIT, I FIXED IT!

This was my first time actually diagnosing a probable PCB failure cause (with a very good hint from @irepairsega) and replaced an IC. And it worked!

For some reason, getting the old IC91 out was a nightmare. 12 of the pins desoldered cleanly with my Hakko 301 and a little cleanup with some braid. But 2 of them just had solder somehow stuck kind of in the middle of the PCB. I kept adding solder and then trying to suck it back out without luck, the braid didn't work, it was a total nightmare. I spent almost 3 hours getting those two holes cleared and thought I was going to destroy the pads along the way. Finally got whatever was blocking the holes knocked lose using a needlepoint tip on my iron and using a light "drilling" motion.

Anyway, once that crap was resolved, the new socket went right in, I replaced the old 74LS125 with one of the replacements I got from Mouser, and the video came right up after reconnecting it. I played several games and went through the test menus and all was working!

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For some reason one of the coinage DIP switches seems to be stuck "on" despite being physically in the off position resulting in coin slot 2 giving 5 credits instead of 1, but I'll look into that some other time.

Next up (after actually mounting the monitor bezel and tinted plexi properly…) will be installing the little toy I received today from @RiddledTV! Outrun/Turbo Outrun multi coming up!

IMG_2798.jpeg

Thanks very much to everyone on this thread that offered advice and offered to help. I'm pretty stoked I actually fixed this thing on my own though!
 
HOLY SHIT, I FIXED IT!

This was my first time actually diagnosing a probable PCB failure cause (with a very good hint from @irepairsega) and replaced an IC. And it worked!

For some reason, getting the old IC91 out was a nightmare. 12 of the pins desoldered cleanly with my Hakko 301 and a little cleanup with some braid. But 2 of them just had solder somehow stuck kind of in the middle of the PCB. I kept adding solder and then trying to suck it back out without luck, the braid didn't work, it was a total nightmare. I spent almost 3 hours getting those two holes cleared and thought I was going to destroy the pads along the way. Finally got whatever was blocking the holes knocked lose using a needlepoint tip on my iron and using a light "drilling" motion.

Anyway, once that crap was resolved, the new socket went right in, I replaced the old 74LS125 with one of the replacements I got from Mouser, and the video came right up after reconnecting it. I played several games and went through the test menus and all was working!

View attachment 842222View attachment 842223View attachment 842224

For some reason one of the coinage DIP switches seems to be stuck "on" despite being physically in the off position resulting in coin slot 2 giving 5 credits instead of 1, but I'll look into that some other time.

Next up (after actually mounting the monitor bezel and tinted plexi properly…) will be installing the little toy I received today from @RiddledTV! Outrun/Turbo Outrun multi coming up!

View attachment 842225

Thanks very much to everyone on this thread that offered advice and offered to help. I'm pretty stoked I actually fixed this thing on my own though!
they're multi layer boards. the +5V and ground traces will be in the middle. I run soldering iron at 750 F and Hakko FR-301 at the 2.5 temperature setting. I arrived at these temperature settings replacing caps on computer motherboards and it worked perfectly. you may just need to leave the Hakko on to heat up longer too.
 
they're multi layer boards. the +5V and ground traces will be in the middle. I run soldering iron at 750 F and Hakko FR-301 at the 2.5 temperature setting. I arrived at these temperature settings replacing caps on computer motherboards and it worked perfectly. you may just need to leave the Hakko on to heat up longer too.
Thanks! I suspected there was a reason the board was so thick. I eventually did turn my iron up from 650 to 750 and also bumped the FR301 up to about 2.5 like you said but then I started to scorch one of the pads (I'd already been molesting it for over an hour) so I backed the iron back down to 700 and switched to the long needle tip.

Lesson learned for future game board repairs!
 
Thanks! I suspected there was a reason the board was so thick. I eventually did turn my iron up from 650 to 750 and also bumped the FR301 up to about 2.5 like you said but then I started to scorch one of the pads (I'd already been molesting it for over an hour) so I backed the iron back down to 700 and switched to the long needle tip.

Lesson learned for future game board repairs!
yeah always make sure to add new solder first. otherwise it's kind of like running a car with no oil.
 
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yeah always make sure to add new solder first. otherwise it's kind of like running a car with no oil.
I've noticed that sometimes on certain boards I have a really hard time getting new solder to actually stick to the old stuff. Is that a temperature thing? Or a solder composition thing (like lead vs lead free)? Or just poor technique?
 
I

I've noticed that sometimes on certain boards I have a really hard time getting new solder to actually stick to the old stuff. Is that a temperature thing? Or a solder composition thing (like lead vs lead free)? Or just poor technique?
I prefer Glowcore, but the place I work buys whatever Kester they find on Amazon. which is reckless. the 63/37 stuff with the flux in it is what you want.

if the solder is scummy and like concrete then I escalate to the dremel wire brush to clean it up. you learn technique when you fix people's battery leak boards for many years. lol
 
I am glad this was fixed, it is a great feeling!

I guess you are ready for this "beast" next, details in my post here

p
 

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I am glad this was fixed, it is a great feeling!

I guess you are ready for this "beast" next, details in my post here

p
Already there!

IMG_2810.jpeg

Just trying to figure out the best place to mount the switcher. Being that it doesn't have the locking latches for all the cables in thinking maybe on the inside wall of the cabinet and then just run the switchers ribbon cables to the boards on the door. Like this:


IMG_2814.jpeg
 
That's where mine is. I think the switcher has some holes around the connectors, and I used those in combination with zip ties to keep the cables firmly seated.

p

PS It looks great…
 
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