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Dead Asteroids fix log

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Nes4life View Drop Down
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    Posted: 04 Feb 2018 at 8:40pm
Got another Asteroids PCB that is nearly fully resurrected.


Issues:
- logically dead but getting correct power. Someone had stolen the 12MHz crystal! £1.70 and 2 days later I have a handful of crystals and the game gives me beep codes
- Beep codes point to the 2114 at R4 being dead. Ripped it out, socketed, and replaced. 
- DIPS are smashed - replaced DIPS (can be confident they work now)
- Game plays garbled and test grid only shows crossing points. Working backwards from the DACs I see that the signals coming out of the LS374 at B10 (Y-signals) do not match the signals going in. Ripped it out, socketed, and replaced. 
- Got a very familiar arrow head pattern < > (see pics below) showing an X-axis issue. Experience tells me its the LS374 at D10. Ripped it out, socketed, and replaced. 
- Game plays but text becomes tiny and left-aligned on the screen. Turns out the LS14 at B6 has pin 4 stuck low. Ripped it out, socketed, and replaced. 

Here's a picture of everything I had to replace to get it to its current state:

Here's the R4 2114 RAM replaced and the DIPS still needing to be swapped out:

Here's the random crossing points only on the test grid. For future reference; this means that both LS374 at B10 and D10 are dead!

Here's the familiar issue when there's a bad X-pos LS374 at D10:

And here's the missing crystal (yet another reminder why you should throughly look a PCB over on both sides before hooking it up - your eyes are a great diagnostic tool):

So, that leaves me with the current state. Game plays and sounds great but when you get to the 'enter top score' screen all the text is left-aligned. I also now notice that all in-game text is tiny:

In the cab (before fixing text issue):

And finished:


Edited by Nes4life - 07 Feb 2018 at 8:41pm
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Mitchell Gant View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mitchell Gant Quote  Post ReplyReply Direct Link To This Post Posted: 04 Feb 2018 at 10:06pm
You're getting good at Asteroids fixing there Phill! Great stuff.

Missing 12MHz crystal is a classic easy-to-miss fault, as it gives a very dead board for the unwary.

Broken DIPs seen very common too. Not sure why? Maybe from people stacking PCBs, it rips tops off?

Text all aligned to the left is a new fault I've never seen, and I can't think of a simple reason what could cause a fault like that either. Pretty sure text drawing position is coded into the software, so wonder how a hardware fault could affect that?
Boy, is this a machine!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Nes4life Quote  Post ReplyReply Direct Link To This Post Posted: 04 Feb 2018 at 10:34pm
I’ve a feeling the text is not really left aligned but just small. The starting x position remains unchanged so it appears all text has gone left. It must be a bad scale signal.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Nes4life Quote  Post ReplyReply Direct Link To This Post Posted: 07 Feb 2018 at 8:34pm
Fixed it! The LS14 at B6 had pin 4 stuck low. Replaced it and all is well.
Saw from a few repair logs online that as well as the 4 scale signals there was also DVX11 that affect sizes. Followed the signal about and it led me to B6 and I saw it misbehaving on the scope.




Edited by Nes4life - 07 Feb 2018 at 8:37pm
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smarty View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote smarty Quote  Post ReplyReply Direct Link To This Post Posted: 07 Feb 2018 at 8:50pm
Thanks for continuing to post these fix logs Phill. Nicely detailed with all the marked up photos and stuff!

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mark H Quote  Post ReplyReply Direct Link To This Post Posted: 07 Feb 2018 at 9:18pm
Great stuff - really interesting - great game too ! 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Hurray Banana Quote  Post ReplyReply Direct Link To This Post Posted: 07 Feb 2018 at 10:27pm
Great stuff
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Post Options Post Options   Thanks (0) Thanks(0)   Quote rushfan86pw Quote  Post ReplyReply Direct Link To This Post Posted: 18 Feb 2018 at 9:37pm
Sure wish you were my next Door neighbor . I have an asteroids cocktail that is dead. Replaced big blue,and have done some other minor power supply testing with a multimeter, but it is very overwhelming to a newbie repair guy with 10 arcade games.
I will inspect the pcb and see if anything looks funky. Thanks for all the info and pictures.
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