Berzerk - Only 7 beeps

kennyboy

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I got a beautiful Berzerk yesterday that was shipped a considerable distance to me.

Upon turning it on for the first time, there was no vertical deflection and all I was getting was a single horizontal line in the center of the screen. The vertical deflection board on the monitor chassis was nearly completely unseated from vibration during the shipping, so reseating that board solved that problem and my Berzerk was working perfectly for a couple of hours.

Then, right in the middle of a game, the screen went dark.

Booting up now only gives 7 flashes/beeps, instead of 8, and the game does not boot.

The monitor is on and functioning, but nothing ever comes up on the screen. Switching DIP switch 9 ON, which is supposed to bring up a diagnostic screen and/or crosshatch pattern, and then reseting does indeed make the LED come on and stay on, and I can hear a change in the buzz of the monitor like the screen is showing a different image, but nothing actually shows on the screen. It's not completely off, there's just nothing but the glowing back background of a blank monitor image.

I just read back throuh every Berzerk related post on here I could find back to 2003.

Right before the game stopped working, I was playing a game and ran directly into a wall, which should have killed me, but the game acted like I had just exited the room and did the "chicken fight like a robot"' and scrolled to the next maze (which I thought was weird) and then died a few seconds later.

Is there anything obvious that pops in anyone's mind when it stops after the 7th beep?

I've read the 7th beep info in the PDF manual, but it hasn't helped.

I'm hoping someone on here knows of something obvious I should try.

Any advice from someone who's been here before would be greatly appreciated.
 
If it makes it past 3 beeps, which it does, then that means that the Z80 CPU (since it's on the ZPU board) is OK doesn't it?

I have reseated all ribbon cables.

Still, just 7 beeps and no Berzerk.
 
If it makes it past 3 beeps, which it does, then that means that the Z80 CPU (since it's on the ZPU board) is OK doesn't it?

Means the Z80's mostly ok, but NMI could still be bad...

Check the cables and such for starters... the NMI gets generated on the VFB and goes through 2 cables and the BSC to get to the ZPU.
 
I removed, inspected and reconnected the pair of ribbon cables that go from the VFB to the BSC, and the pair that go from the BSC to the ZPU. (a total of 4 cables)

I also used my multimeter to check the voltages on each side of the cables, at all of the pins, to see if whatever voltage was being generated on one side was being passed across to the other side. I'm very new at this, but that seemed like a logical thing to do.

Is it common for a Z80 to fail in a game? It IS listed as a possible culprit in the Berzerk manual for failure after the 7th beep.

I notice they are not expensive, so I guess I will order one and replace mine to see if that helps. It just seems odd that the main CPU of a game would fail just a few hours after I received it. Of course, I guess the original Z80 is 31 years old, so perhaps it's NOT unusual for it to fail. I noticed that the chip feels extremely hot to the touch. Not sure if that's normal or not.

After the game failure, I DID check the 5+ on the ZPU board. Again, I'm new and that was the only thing I knew to do (just getting started with Randy Fromm materials). There are stickers around the Berzerk boards that say to adjust it to something between 5.00V and 5.25V. Mine was actually higher at 5.58V, so I used the adjustment and lowered it to 5.17V.

The game still doesn't work, but I wonder if the long trip could have jostled things enough to increase my 5+ which somehow damaged my Z80?

At any rate, since the game started acting weird right before it failed, with me walking into a wall, which should have killed me, and the game acting like I legally exited a room, I am leaning toward the idea that perhaps the Z80 is not functioning.

I will order one, replace, and keep my fingers crossed.

If that doesn't work, I don't know what I will do because all of those other NMI related chip locations appear to be soldered-in chips and I have no idea what they are.

I hate that my new Berzerk isn't working, but I also really want to learn to repair these beasts, so I guess this is really a good game to learn on, since the boards are so accessible. I just hope it's something that won't be too difficult for a first time. I keep telling myself it can't be THAT bad since I've got 7 out of 8 beeps.
 
When these arcade games get this old, it's best to check all the connectors, exercise all the switches and reseat all the chips. According to the manual, the 7th beep indicates one of the problems could be the dip switches. I suggest toggling them a few times and then put them back into the setting they were in when the game worked before.

You also mentioned the +5 volt was a bit high before. This sometimes happens when one of the power supply electrolytic capacitors fails. Turning it down won't help much. I suggest you find someone who can loan you an oscilloscope and look at the +5 voltage. If it has a high ripple of about 50 millivolts or more, one of the caps may have failed and will need to be replaced.
 
OK folks, how about this?

I tried out a new test procedure I just learned about and used the diode test setting on my multimeter to check each pin of the Z80.

I'm sure some of you are familiar with this test.

I put the red probe in ground and probed with the black probe per the test procedure.

As I understand it, if the IC is good, then there should be a reading (usually 0.5) on each pin of the IC, even with no power to the board, which is how I checked this.

Absence of a reading, or a really low reading indicates damage to the IC.

Well, sure enough, every pin gave a reading of 0.5 except one.

There was one pin that read 0.001.

I checked another chip or two for good measure, and all of their pins read 0.5.

I then powered up the board, listened to the 7 depressing beeps, and then started measuring my +5V directly on the chips themselves using the most upperleft pin, which is usually supposed to be +5V.

I checked all kinds of chips and kept getting +5.17V, which is what I adjusted the +5V to the other day.

BUT, when I check it on the Z80 chip itself, it only reads +3.84V!

Hmmmmmmm...

Do you think this low voltage on the +5V pin of the Z80, along with the fact that one of the pins gave the super low reading when using the diode test on the multimeter could really mean that there is something wrong with the Z80 itself?

It's listed as a possible culprit for my problem in the Berzerk manual, and even though I'm new and just learning this stuff, these results seem to be saying that there is something abnormal with the Z80 chip.

Am I on the right track with my detective work?

I've seated and reseated and swapped ribbon cables and checked continuity across them.

There don't seem to be any problems there.

These abnormal readings on the Z80 make me think it's time to pop it out and replace.

Anyone who is familiar with these tests who agrees?
 
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Ack!

It's fine on voltage then.

Pin 29 is the one that "failed" the diode test, but if that's the ground then I guess there's nothing wrong.

Curses.

OK I just checked all the possible culprit chips listed in the manual using the diode test function on my multimeter.

They all gave readings (usually around 0.5) on all pins except the ground.

As I understand it, that means the ICs are good.

I guess I'm going to have to pay someone to figure this out.

P.S. Thanks MrGorf for the info. I guess I should've looked up the pinout on a Z80. I guarantee I will remember that from now on. I'm learning, slowly but surely.
 
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I think I may have found the culprit now.

I went back and CAREFULLY checked all of the ICs identified in the Berzerk manual as possible causes of failure after the 7th beep.

I used the diode test setting on my MM with the red lead on GND and the probed each pin of each IC with the black lead, looking for the junction drop of 0.5-0.9 on each pin excluding the the Vcc and GND.

The IC located at 1E on the VFB board appears to have a problem. It's a Motorola sn74ls02n.

All of the pins on that IC show the junction drop (I hope that's the right term, correct me if it's not) of 0.5 or so except pin 3 which failed and showed 0.001. (of course the ground pin 7 also showed that but that's normal)

Pin 3 is not the ground, so I believe there is a problem with that chip.

Is that correct?

If that DOES point to a problem with this chip then I assume I need to replace it.

Unfortunately it's soldered in and I have yet to attempt my first soldering job. I guess it's a good time to learn huh?

Does it matter if the new sn74ls02n is made by TI? The old one is Motorola.

Does this sound like I might be on the right track?
 
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I've never seen or heard of 'testing' ICs in this manner before.

Most digital logic chips have a couple of pins for power (+5V and ground) and the other pins are either inputs or outputs (or both). Inputs can be tied high or low or be fed by the outputs of other logic ICs.

I'm not sure what the diode check on individual pins would reveal.

K
 
I learned it from some arcade repair training materials. It seems to be a novel method.

Has something to do with the fact that the ICs are TTL.

Hooking the red to the ground, while the machine is off, and then probing each pin of the IC is supposed to return a junction drop of 0.5-0.9 if the IC is functioning properly, even though the test is done with the machine power off.

A very low reading (0.001) is supposedly indicative of a failure of some type in the IC.

Apparently this is a way to check for the proper function of an IC without even needing to know exactly what it is or what it does.

Excluding the +5V pin and the ground, all other pins should return 0.5 or so if the IC is functioning correctly and 0.001 if there is a problem.

Every pin of every IC listed as a possible cause of the problem I've got that I have checked has returned 0.5 except pin 3 on the IC @ 1E. That's why I think that IC may be the problem, if this unusual type of test does indeed work.

Just found a mention of this quick test here:

http://s107351202.onlinehome.us/cgi-bin/Blah/Blah.pl?m-1283046076/
 
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You have to look at the schematics, or at least the traces though... I just happened to have a VFB board next to me, and looked... pin 3 on 1E is tied to ground, which is almost certainly why you're getting that reading.

DogP
 
I think you should get something on the screen when it gives 7 beeps, do you see anything like a "map" of boxes ? (The screens may cycle). ?

If so, try to see if one of those boxes is filled/white. If so there may simply be a bad RAM.

[Edit] Mmmm, 7 beeps may not be the RAM.

Something very obvious that the manual says (but could still be the cause):

Check that Dip Switch 2B (Pins 3-6 and 2-7) is set to on....

Do your boards have any battery leakage damage ?
 
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