Battlezone AUX board troubleshooting

douglasgb

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Hi all,

I have eight BZ AUX boards in various states of disfunction. Some show L, some H, and some T. There's even one that shows no error but has the radar blip sounding constantly (even in attract). This thread is to detail the troubleshooting process and techniques used to find and fix whatever problems exist on each board.

First, the sockets on these boards seem to come in two varieties: bad and really bad. It's a lot of work, but replacing at least the BPROM sockets in row one is essential for reliability. I'll be replacing them and the five 40-pin sockets to really make the boards as good as they can be. The good news is you can pry up the plastic housings of the sockets to make it easier to desolder the pins individually.
 
Good thread topic. Subscribed.

I think you'll find that replacing the sockets will fix about 90% of H and L mathbox errors (if the issue isn't a bad 2901).

As for the radar blip, that one I've seen. IIRC, check the 4066 at L4, which is the master sound enable. If it gets stuck on, you'll hear the radar playing all the time.
 
Those 30+ year old sockets have seen better days. I doubt very much if the original builder ever thought they would still be in use 10 years later, let alone 30+ years.

To bad they are kind of a pain to change out.
 
Prying up the plastic housings of the sockets is pretty easy. These are right against the board so I use the two holes to rock it up a bit and then pry with a small flat blade.

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For the BPROMs I'm using regular sockets but for the bit slicers I'm making my own on the theory that every little bit of airflow will help. I have a bunch of 40 pin single row headers that I cut in half, and then use a complete socket to align.

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But the POKEY will get a normal socket.
 

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Before soldering in the new sockets I inspect the holes to make sure all is well. The little bit of splash in hole 13 might flow onto the pin but maybe not. Lightly zigging the clean smooth tip of the soldering iron over the holes normalizes them.

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Here's one board's worth of removed pins. I'm rich!

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Also, since I am doing so many, I built the signature analysis harness:

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OK with all the prep work done, we're on to board #1. All sockets have been replaced and known-good BPROMs and bit slicers installed. Self test reveals a 'T' for math box time out error, so the first thing to do is probe for the 3MHz and 6MHz clocks, and Eɸ2 which should be 1.5MHz.

All three signals are arriving on the board. 6MHz only needs to go as far as pin 4 of B4 and it does. The 3MHz signal is really the heartbeat of the board and goes several places as shown on sheet 3B of the schematics. It feeds into B4p2, J4p2, D3p1 and D4p8. That one's is important as it then exits Dp10 to go on to be the clock for both LS161s at D1 and E1 as well as the flip-flops at C1 and C5.

The signal does make it through D4 but does not make it through the inverter LS04 at E4 (goes in pin 11 but nothing coming out of pin 10). Will replace that chip.
 
Replacing E4 did not help - still no output even with good input. Normally that means the next chips are dragging down the output, and normally I test for that by leaving the output pin out of the socket and testing it. In this case there is no output on the disconnected pin!

Taking another look at the input E4p11, the waveform coming out of D4p10 is a 1.5MHz square wave but it does not go from 0 to 5v... it is weak.
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Full waves go in (to D4) at 3MHz test point and D4p8 input pin.

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Dribbling out of D4p10. Weak!

So now I'll replace the LS02 at D4.
 

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D4 was OK. This time it is something dragging down the output since with the pin hanging in space I get a full wave but it gets truncated as soon as the pin in connected:

http://www.gauck.com/arcade/BZ/clock.mov

The output goes to E4 which was already replaced. Thankfully pulling it isolates the two flip-flops it feeds. The output also goes to D5, D1, E1, C5, and all four bit slicers. Pulled the 2901s and no change. D5 was already socketed when I got the board and pulling it makes no difference. That leaves D1, E1, and C5.

There may be ways to increase the odds of picking the right chip (LeakSeeker, testing resistances, Randy Fromm's 6v lantern battery trick) but with just three I'll take my chances. I did put the comparator on each of them but with the clock pin being the culprit I was not surprised it did not detect any discrepancies.
 
Grrr. Turns out it was none of those remaining three chips. Pulling them all (OK< actually just the relevant pin from each) and the signal is still being clipped. SO it must be a shorted trace.

The signal goes to all four of the bit slicers via pin 15, and because of a tiny solder splash like the one shown in post #5, it was shorted against pin 26. That's A15 between the BPROMs and the 2901s.

Removing the short fixes the time out error, but it is replaced by an L.

Doing quick signature analysis reveals that pin 12 of BPROM J1 is wrong, which is A15. Looks like shorting a 3MHz signal into the output of a BPROM killed it.

After replacing J1, the board is fixed!

The moral? Always check previous work, even when that work is your own!
 
As for the radar blip, that one I've seen. IIRC, check the 4066 at L4, which is the master sound enable. If it gets stuck on, you'll hear the radar playing all the time.

You are correct sir. Someone had shorted pins 10 and 11 with a solder blob. Removed the blob and get no sound at all. I guess that's why the input and output were shorted. Replaced the chip (it crumbled as I clipped it out) and all is well with board #2.
 
Subscribing and thanks. Maybe motivation for me to build my harness and use KK sig2 to finally address my 3 non working aux boards.
 
I love Battlezone. First game I mastered. Keep posting. You board repair guys are amazing !
You know in the early 80s that signature analyzer was a 900 dollar high tech piece !
 
Subscribing and thanks. Maybe motivation for me to build my harness and use KK sig2 to finally address my 3 non working aux boards.
In the spirit of bumping and sharing, I did make a harness but have never used it; sold my KK sig2 but still have HP analyzers. I think I wired it up correctly.
 

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