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Faulty galaxian p.c.b.

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positive logic View Drop Down
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    Posted: 30 Jun 2020 at 9:36am
I wonder if any of you guys could help me with a faulty galaxian p.c.b which is showing a flickering "BADRAM 1" and occasionally a screen full of coloured numbers , letters and garbage.
The board in question had been hacked to run another game which had problems so I removed all this and put the board back to original.
I`m using known good glax roms borrowed from a working board.
I have replaced lots of chips so far including the rams at 3F,3H,4F,5F,7N,7P.
I`ve got the galaxian fault finding guide and circuit diagrams.
Some imfo that might help is the VRAM lines 6&7 on the vram data bus are missing on chips 3F,3J & 5F , these lines being low and the chips have been replaced.
All the pins on 5L read low except pin 11.
All the inputs to chips 4M & 5M from the horz position bus are low.
I`m only an ammeter at fixing these boards and this one has got me stumped so any help would be appreciated.

Robin
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Lurch666 Quote  Post ReplyReply Direct Link To This Post Posted: 30 Jun 2020 at 10:06am
When you removed the hack did you fix any cut traces?
As far as I know hacks like this require some traces to be cut and if you missed one this might be causing your problem.
You rang......?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote positive logic Quote  Post ReplyReply Direct Link To This Post Posted: 30 Jun 2020 at 10:17am
Yes I fixed the cut traces , only 3 of them.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote andyman Quote  Post ReplyReply Direct Link To This Post Posted: 30 Jun 2020 at 10:17am
Have you replaced the LS245 buffers for the ram ?

Macro has a good guide here

http://www.macros-arcade.com/galaxianfix.htm


Initial tests indicate
       unit OK
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Post Options Post Options   Thanks (0) Thanks(0)   Quote positive logic Quote  Post ReplyReply Direct Link To This Post Posted: 30 Jun 2020 at 10:31am
Yes andyman both 245,s been replaced.
I`ll check out that link.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Lurch666 Quote  Post ReplyReply Direct Link To This Post Posted: 30 Jun 2020 at 10:59am
Have you checked the 8216 at 8H pins 2 and 11 for activity?
You rang......?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote positive logic Quote  Post ReplyReply Direct Link To This Post Posted: 30 Jun 2020 at 11:46am
My board uses the 74LS245 instead of the 8216`s in position 9B.
I have activity on all pins.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote philmurr Quote  Post ReplyReply Direct Link To This Post Posted: 30 Jun 2020 at 12:13pm
Originally posted by positive logic positive logic wrote:

All the inputs to chips 4M & 5M from the horz position bus are low.


So HPOSI isn't being generated, check the outputs from RAM 4F & 5F and WE (pin 20)

Then check outputs from 8P (pin 12), 8H (pins 12,13) & 8M (pins 12,13)



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Post Options Post Options   Thanks (0) Thanks(0)   Quote positive logic Quote  Post ReplyReply Direct Link To This Post Posted: 30 Jun 2020 at 1:36pm
Hi Phil
The checks are as follows

4F  pins 8,10,12,14,16,18 & 19 are low,  pin 17 is high , activity on pin 20
5F  the same as above.
8P  activity on pin 12.
8M  activity on pins 12 & 13.
8H not fitted to my board as mentioned in an earlier post.

Robin
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Post Options Post Options   Thanks (0) Thanks(0)   Quote philmurr Quote  Post ReplyReply Direct Link To This Post Posted: 30 Jun 2020 at 1:48pm
Originally posted by positive logic positive logic wrote:

Hi Phil
The checks are as follows

4F  pins 8,10,12,14,16,18 & 19 are low,  pin 17 is high , activity on pin 20
5F  the same as above.
8P  activity on pin 12.
8M  activity on pins 12 & 13.
8H not fitted to my board as mentioned in an earlier post.

Robin


Sorry not 8H, check 8N 12 & 13
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Post Options Post Options   Thanks (0) Thanks(0)   Quote positive logic Quote  Post ReplyReply Direct Link To This Post Posted: 30 Jun 2020 at 2:25pm
Hi Phil
Just checked 8N pins 12 & 13 and there both high.
I had doubts about this chip a few days ago and replaced it but made no difference.

Robin 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote philmurr Quote  Post ReplyReply Direct Link To This Post Posted: 30 Jun 2020 at 3:07pm
Can you download the test ROM and see what results you get? https://www.jammarcade.net/files/ROMs/Diagnostic/Galaxian_test_ROM.zip

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Post Options Post Options   Thanks (0) Thanks(0)   Quote positive logic Quote  Post ReplyReply Direct Link To This Post Posted: 30 Jun 2020 at 3:19pm
I kind of knew this question was coming.
I don't have a test ROM and have never programmed a rom in my life.
I do have a chip programmer but have never used it , I`ll dig it out and see what I can do.
I`ll be seeing a friend on Thursday who could do this for me.

Robin
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Post Options Post Options   Thanks (0) Thanks(0)   Quote positive logic Quote  Post ReplyReply Direct Link To This Post Posted: 02 Jul 2020 at 4:12pm
Never found my eprom programmer so got my friend to make the test rom for me.
Test is rom now fitted and here`s what happened.
Coloured garbage followed by a screen full of zero`s , then the words " ram stuffed " and the numbers 4000  42  40 at the top of the screen.
Hope this helps.

Robin
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Curseur Quote  Post ReplyReply Direct Link To This Post Posted: 02 Jul 2020 at 4:24pm
I tend to believe that you checked everything that has to be checked in the main CPU area.
Keep inspecting for cut traces.
Galaxian PCBs have sockets that tend to be flacky over the years. If nothing else works, try reseatting the eproms with some contact cleaner.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote philmurr Quote  Post ReplyReply Direct Link To This Post Posted: 02 Jul 2020 at 4:36pm
Originally posted by positive logic positive logic wrote:

Never found my eprom programmer so got my friend to make the test rom for me.
Test is rom now fitted and here`s what happened.
Coloured garbage followed by a screen full of zero`s , then the words " ram stuffed " and the numbers 4000  42  40 at the top of the screen.
Hope this helps.

Robin


Ok that shows it's reading $42 from location $4000 where it should contain $40, which is the very first location read.

If you've replaced the RAM at 7N & 7P my guess is unless your replacement RAM at 7P is also faulty then there's a broken track on bit 1 of the programme RAM.

Check 7P pin 13 and pin 12 of 9B


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Post Options Post Options   Thanks (0) Thanks(0)   Quote positive logic Quote  Post ReplyReply Direct Link To This Post Posted: 02 Jul 2020 at 5:41pm
Wow phil , didn`t expect you to get back to me so quickly.
The logic probe is pulsing away nicely on 7P pin 13 and 9B pin 12.
I`ve put the test rom in the nearest socket to the micro p , is this correct ?

Robin
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Post Options Post Options   Thanks (0) Thanks(0)   Quote philmurr Quote  Post ReplyReply Direct Link To This Post Posted: 02 Jul 2020 at 7:34pm
Originally posted by positive logic positive logic wrote:

Wow phil , didn`t expect you to get back to me so quickly.
The logic probe is pulsing away nicely on 7P pin 13 and 9B pin 12.
I`ve put the test rom in the nearest socket to the micro p , is this correct ?

Robin


Yes the test ROM is in the right place. For completeness please swap 7P and 7N

Also what’s the status of 7P pins 8 & 10?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote positive logic Quote  Post ReplyReply Direct Link To This Post Posted: 02 Jul 2020 at 7:48pm
Swapped chips 7N , 7P no difference.
Pin 8 is high and pin 10 is pulsing.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote philmurr Quote  Post ReplyReply Direct Link To This Post Posted: 02 Jul 2020 at 8:10pm
Ok the RAM isn’t being selected.

Check 2N pins 4, 5 & 6

8M & 8N pin 15
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