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Asteroids repair for Virtvic

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Nes4life View Drop Down
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    Posted: 21 Dec 2017 at 11:20pm

Symptom: Test grid made up out of arrows (up and down).
Fix: replaced LS374 at B10 (if arrows are left and right then replace LS374 at D10).

Symptom: Random ellipses where rocks or other objects should be and test grid is a little fuzzy in parts.  
Fix: replaced TL082 in Y section (but could well be the other TL082!)

Symptom: No explosion sound.
Fix: replaced both (!) LS164 at R9 & P9

Symptom: No saucer sound.
Fix: replaced 566 at P10.

Symptom: Game plays blind in the cab but fine on an oscilloscope. Z-out is dead.
Fix: replaced a 3rd (!) LS164 at K9

---------
Virtvic sent me his Asty PCB as it had an interesting visual issue on the test grid:



Looks like a Y-axis issue, so I made the bad assumption it was probably the DAC or 4016B. After needlessly desoldering & socketing them I realised I should stop being an idiot and actually look at the problem. I got the oscilloscope probe out and checked the outputs of the IC that feeds the Y-DAC (a LS374 at B10):


Lo and behold! Pin 5 had a dodgy output and pin 4 (which is the input for this signal) was fine.
This is a good example of an issue you couldn't uncover with a logic probe.
Pin 5 (the reading on this pin should look near identical to pin 4's reading - it might not look like a bad signal but it's very different to the others and doesn't match the one from a working PCB.):

Pin 4 (this looks the same on another working Asty):

So, not having any LS374 to hand I did the classic test of switching two ICs on the same PCB:


Before (Y-axis issue):


After (X-axis issue):


So, confident this was the issue, I desoldered & socketed a spare from another Asty PCB. The result was OK but a little blurry and there were some dodgy ellipses:


Looked very much like a vector output-area issue so I desoldered & socketed the TL082 in the Y-axis and lucked out! Fixed with the first replaced IC:



In celebration I fixed the LEDs on my pimped-up harness (they show the player button lights - note the switch for selecting between Asteroids and Asteroids Deluxe):



Next issue - there's no explosion sound. Stay tuned.



Edited by Nes4life - 06 Jan 2018 at 10:19pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote virtvic Quote  Post ReplyReply Direct Link To This Post Posted: 22 Dec 2017 at 5:28am
Excellent stuff. I wish I knew how to do all this stuff!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote smarty Quote  Post ReplyReply Direct Link To This Post Posted: 22 Dec 2017 at 7:05am
Good fix :)

Edited by smarty - 22 Dec 2017 at 7:05am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote t-m Quote  Post ReplyReply Direct Link To This Post Posted: 22 Dec 2017 at 8:21am
Nice one :)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Hurray Banana Quote  Post ReplyReply Direct Link To This Post Posted: 22 Dec 2017 at 8:57am
nice bit of fixing phil, you're getting good at this
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Post Options Post Options   Thanks (0) Thanks(0)   Quote dj_yt Quote  Post ReplyReply Direct Link To This Post Posted: 22 Dec 2017 at 9:01am
Always good to see a successful repair. Well done Phil!
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Equites Quote  Post ReplyReply Direct Link To This Post Posted: 22 Dec 2017 at 9:18am
You should add these to ‘Repair Logs’.
Atari PCB's (and most non-Atari), AR2's, Vector Deflection/HV boards repaired & refurbished.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ianski Quote  Post ReplyReply Direct Link To This Post Posted: 22 Dec 2017 at 9:38am
Excellent work Phil!

On a side note I had a cool old Gould bench multimeter that was my Dad's old one, now long gone sadly.
Looking for: Nice working monitors for my US games.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Nes4life Quote  Post ReplyReply Direct Link To This Post Posted: 22 Dec 2017 at 10:24am
I'm happy for an admin to move all my repairs to the 'Fix Logs' section. I'll be sure to put them there in future!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote virtvic Quote  Post ReplyReply Direct Link To This Post Posted: 22 Dec 2017 at 10:27am
I’d like to hang around when you’re doing a repair to get some much needed tips!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DanP Quote  Post ReplyReply Direct Link To This Post Posted: 22 Dec 2017 at 11:04am
Moved to Fix Logs as requested :)   Nice fix btw, and cool to show your method.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Nes4life Quote  Post ReplyReply Direct Link To This Post Posted: 22 Dec 2017 at 1:13pm
So, now onto the explosion sound. I think it's the noise generation used for explosions and for thrust. I have a hard time testing the thrust sound on my rig as it's practically inaudible when working (I usually check it in my cab as a last play test). 

Anyway, here's the overview of the explosion sound schematics:


I first put a scope on 'EXPLOSND' at the end and see nothing when there should be an explosion. I take a reading at point 2 (pin 9 of R8) and again there is nothing. I took a CLK reading from pin 11 and that was fine. Finally, taking a probe reading from the 'NOISE' input showed there was no noise.

So here's the schematics of the noise generation for the explosions:


I tested N5 (a LS00 NAND gate but configured as a NOT gate by connecting both input pins together) and it was doing its job. I went back to P5 (a LS86 XOR gate) and it too seemed to be doing its job but the inputs were both stuck high. I then checked the CLK reading on both the LS164 at P9 & R9 (pin 8) and it read a healthy 11.8KHZ on my multimeter. So finally I checked the output on pin 13 of R9 and it was stuck high.

So my conclusion is that one of these LS164 are toast (probably R9). I'll order some replacements and update this thread.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote dj_yt Quote  Post ReplyReply Direct Link To This Post Posted: 22 Dec 2017 at 1:39pm
I'm always jealous when I see some of these older schematics, they are so clear compared with the later Sega scans! 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote philmurr Quote  Post ReplyReply Direct Link To This Post Posted: 22 Dec 2017 at 6:06pm
Great graphics fix and nice write-up Phill - good luck with the sound...


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Nes4life Quote  Post ReplyReply Direct Link To This Post Posted: 23 Dec 2017 at 8:42pm
Well, would you believe it, both LS164 had died! Pulled one (R9), checked it was dead, replaced it and got some crazy single tones on each explosion (rather than nothing). Output of R9 looked good but the 'noise' signal was still crazy. Pulled the other (P9), checked that was dead too, replaced it and got the explosions back! Would never have thought both would go; but there it is.



Next up... saucer sound is missing.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Nes4life Quote  Post ReplyReply Direct Link To This Post Posted: 24 Dec 2017 at 8:38pm
Saucer sound is back! 566 had died. 
  1. Check M10 pin 4 is triggering 'SAUCRSNDEN' - 'twas indeed.
  2. Piggyback 4016 at N10 (these do a lot in this circuit and fail often) - no change.
  3. Piggyback 555 at R10 (cheap to replace!) - no change.
  4. Piggyback 566 at P10 (not that cheap to replace) - sound sprang back to life!
I'll soak test for the next few days


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Post Options Post Options   Thanks (0) Thanks(0)   Quote neil1637 Quote  Post ReplyReply Direct Link To This Post Posted: 24 Dec 2017 at 9:45pm
This is truly inspiring. Great fixing skills.

Now, go and wrap those presents!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Nes4life Quote  Post ReplyReply Direct Link To This Post Posted: 06 Jan 2018 at 1:44pm
OK, so I was playing (soak-testing ) the PCB a couple of days after boxing day and suddenly there was no picture in the cab! I feared my monitor had died but swapping in my own PCB fixed the problem in the cab. So I put Vic's PCB back on the bench and the oscilloscope display was fine. I knew the Z-out had to be faulty as the oscilloscope setup doesn't use / test those signals. 

Short story; the 74LS164 at K9 had died and replacing it fixed the issue. That was the 3rd LS164 on this board which is suspicious. I guess something killed off 2 of them in one go and the 3rd was on its way out.

Long story;

Got the schematics out and Atari have this to say (I'm pretty sure Q1, Q2 and Q3 should actually be Q7, Q8 and Q9):



Here's the schematics and I've marked on them the significant components and the order I checked them in:



Testing the Z-out signal with the oscilloscope I could see there was little activity and floating around 1V. There's only 2 ICs in this circuit - H10 is used as a NOT gate and K9 actually does the heavy lifting. Checking the signal out of K9 at pin 3 showed a weird signal that didn't look anything like what was coming out of the healthy IC on a working PCB. I did a quick check of the inputs and all were fine (pin 8 clock was around 3MHZ, pins 1 & 2 looked good and pin 9 was high). So I desoldered K9, checked it was dead in an IC tester for good measure (and it was), fitted a socket, reached for another LS164 (fortunately I'd ordered five when the first two had died), and jobs-a-good'n. Put it back it the cab and the game plays rather well.

Here's the actual PCB so you can see how it relates to the schematic:


Think I'll get this PCB posted back to Vic before anything else decides to die! LOL


Edited by Nes4life - 06 Jan 2018 at 1:46pm
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