Starship 1, Video working but noise covering screen [RESOLVED]

HYPERSPACE signal is always low and output pin L10p3 is also always low, whether the garbage on the screen or not. Grounding either didn't change anything.

However, R11p1, if this is grounded the garbage goes away, inputs to this are PHASOR' through a 470 ohm resistor and R10p10. Putting the probe on the right side of the resistor I can hear activity when I fire the phasors during a game that is associated with when I can see the faint lines of them firing on the screen otherwise that signal is always low. Which leaves the output coming from the 7518 as the only other source of the garbage I can find.

Yeah, it's probably something upstream of the PROM in that case.

Depending on the state of ALPHA, PHASOR', CIRCLE, BLANK, and MUX the PROM is disabled, and those signals get coupled to the outputs through those resistors instead.
 
Something else weird about J10 (7406 inverting buffer), output on pin 10 will have a low tone on the logic probe for less than a second and then goes floating/silent. This is /Noise_Freq. Didn't mean to look into this specifically but was curious about trying to hear any audio sounds with the logic probe before they are amplified and output and I was surprised to see J10 involved in that, which had what I thought to be shorted outputs, so started probing and found the above additional issue. Methinks this 7406 is bad. Time to go see if I can find one on-hand.

7406 is open collector...
It pulls to ground when the input is high, and floats with the input is low.

The 3 J10 gates in that circuit pull the caps to ground when the inputs are high, and the current sources (made out of resistively degenerated transistors) ramp the caps back up.
 
Always start with power. Glad I didn't go making any changes yet. Garbage on the screen was not present when using original power brick. 5V only is not sufficient for this board to operate.


Had to also make an interlock-bypass to get it working on bench.
View attachment 680748View attachment 680749

Still need to wire up the pots and put the game through a few other quick tests, but happy to see the board is running!

While pulling the brick from the cab I also checked out the control panel, found one of the pots had a disconnected wire. Perhaps that was the original fault that caused it to be put away?
Congrats on solving it. ALWAYS START WITH POWER.
Power weak - game won't run.
Power dirty (AC ripple) - game won't run.
Power gone - game won't run.
 
Yep, the garbage on screen problem is resolved at this point. New problem is now I'm getting the Unregulated 10V fuse to blow after ~20s.

A Fast Blow fuse only lasts a second or two (first spare I could find), but SBs give me about 20s before the fuse opens. Game appears to work normally during this time but not a lot of time for testing & I don't want to keep popping fuses without a plan.

Screenshot_20230807-172322.png
(Fuse is located just after the MR750's on the power brick, I currently only have a single 18ga wire instead of 4 going to the edge connector)


Manual calls for a 2A SB in this spot, but when I was supplying 5V directly to the board, my bench supply was up to 3.7A. Haven't yet tried to measure actual current through that line yet, I'm thinking I should be able to measure the voltage across the 2 Ohm power resistor then use V=IR to calculate actual current. And failing that approach will put my meter in-line in current mode to check it out. A new stash of fuses and some LM323's arrived over the weekend, so I've got a few things to check. My mind keeps going back to that Stunt Cycle repair I saw with the leakage current issues but don't want to get ahead of myself.

If I haven't gotten it figured out after some basic troubleshooting, I'll post a new thread about it. Edge connector already been cleaned. None of the diodes appear to be shorted on either power brick or game board. Nothing too hot to the touch I could find after the last attempt. Haven't done the fingernail trick on all ICs yet.
 
I'd never actually played Starship1 before pulling it up in MAME yesterday.

As a side note, the circle generator is pretty neat and worth walking your way through to figure out how it works. Took me a sec to notice the inputs of the MC1495s were tied together.

This one might be worth a redesign but MC1495s are pretty expensive at this point.

1691520248393.png
 
As noted in the MAME driver, this schematic is obviously wrong, as it would generate a 11.7kHz HSYNC.

I'm guessing J8, pin 5 is actually on a pullup rather than ground, but it'd be good to confirm.

1691520986667.png
 
Yep, the garbage on screen problem is resolved at this point. New problem is now I'm getting the Unregulated 10V fuse to blow after ~20s.

A Fast Blow fuse only lasts a second or two (first spare I could find), but SBs give me about 20s before the fuse opens. Game appears to work normally during this time but not a lot of time for testing & I don't want to keep popping fuses without a plan.

View attachment 682964
(Fuse is located just after the MR750's on the power brick, I currently only have a single 18ga wire instead of 4 going to the edge connector)


Manual calls for a 2A SB in this spot, but when I was supplying 5V directly to the board, my bench supply was up to 3.7A. Haven't yet tried to measure actual current through that line yet, I'm thinking I should be able to measure the voltage across the 2 Ohm power resistor then use V=IR to calculate actual current. And failing that approach will put my meter in-line in current mode to check it out. A new stash of fuses and some LM323's arrived over the weekend, so I've got a few things to check. My mind keeps going back to that Stunt Cycle repair I saw with the leakage current issues but don't want to get ahead of myself.

If I haven't gotten it figured out after some basic troubleshooting, I'll post a new thread about it. Edge connector already been cleaned. None of the diodes appear to be shorted on either power brick or game board. Nothing too hot to the touch I could find after the last attempt. Haven't done the fingernail trick on all ICs yet.
Did you check the fuse connectors for voltage drop?
Put a probe on the lead in, and one on the fuse barrel in the clip. If you see any voltage, you are dropping voltage and heat across the connector / fuse clip. Just keep moving the probe back.

Connector - Clip - Fuse Barrel closest to clip - Fuse Barrel furthest from clip - Clip - Connector.
 
Will add that to the list of things to check. Thanks!

I'm just surprised that this problem developed after I hooked the pots up. In my video when I had had clear video for the first time, it ran for many minutes at a time without issue, no pots wired up at the time.

Only after I acquired/found some pots and hooked them up did the fuse start popping. Maybe I hooked these up wrong? Maybe the ICs that use them went bad since they were made in 1977? Now the fuse still pops after disconnecting the pots from my test harness. Wires still in harness but pot ends have quick disconnects for easy swapping out.

Bare bones harness was powered on for hours at a time as I poked around, this was when bench supply said it was supplying 3.7A @ 5.7 to get 5.01 at the edge (probably because of poor connections as @ArcadeTechGW mentioned above),
PXL_20230711_010933065~2.jpg

Harness after adding AC lines and 10V from power brick, includes wires for pots:
PXL_20230808_022641377~2.jpg
It was this configuration that worked long enough for multiple videos I took showing it working prior to me getting the pots. After pots connected, 2A SB fuse starts popping after 20s.

Earlier this evening I found some discrepancies in readings for the diodes that rectify the incoming AC, only measured in circuit this far, but I was getting diode readings in both directions on two of them, and the new replacements I got don't do that.
Screenshot_20230808-194202.png
Didn't have time to pull them and check out of circuit, but that's the next plan of attack at this point.

I'm leaving out a few detours I've created/caused in this process, we'll see if they cause more problems later. RIP LM323 from 1977.
PXL_20230808_013351600~2.jpg
 
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