Suicide Battery Questions

troxel

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I recently got two PCBs, Golden Axe and 3 Wonders, and both don't have any sound, but everything else is fine.

Since 3 Wonders is a CPS-1 game, wouldn't the battery take out the graphics and not the sound?

The Golden Axe has a z80, so that would be the suicide battery? Is it possible to replace the z80 with a z80B and replace the two roms? Or, do I have to contact segaresurrection in order to get the board to work again?

Thanks,
Theron
 
Golden axe as far as I know never used a encrypted Z80, it only came with an encrypted 68000 CPU which looks like this..

http://www.retroclinic.com/leopardcats/decrypt/fd1094.jpg

The Z80 is the sound CPU but it should be a stock standard Z80B, if yours is just a Z80 then it will be a problem as it may not run at the 6Mhz that the system16 Z80 is run at.

Bear in mind that the markings on Z80s can be a bit cryptic from some manufacturers so its wise to google to check it is the 6Mhz version. Z80s came in a range of speed (the chips dont' set the speed but their speed is the maximum they should be run at, if they are used in a board that runs them at a higher speed than the chip is rated for, it may simply not work, or it will kill the chip over time.

Z80 - 2.5Mhz
Z80A- 4Mhz
Z80B- 6Mhz
Z80C- 8Mhz
etc ect

In any case the Z80 is socketted on your board so just replace it with another Z80B (check that the old one is the right way round and that you are not going to fry a second chip by copying the original).

That may or may not fix the problem, but I did recently repair a Golden Axe board that had a blown Z80B so its not unheard of for a CPU to die.

There are however a couple of other usual suspects when it comes to a system16 board with no sound...

1) There should be a little blue box about 3mm x 6mm x 10mm that sits above the 40 pin chip that is directly above the Z80, this is the crystal oscillator for the Z80 and its quite fragile, its common for these to be totally missing from boards, they often feel a bit wobbly but that is normal. I assume you dont have a scope to check that the Z80 is getting a clock signal so just check the oscillator is still there.

2) The other problem is quite common, any damage to the two corners furthest away from the (Non-JAMMA) edge connector can impact the sound system. On the solderside there isnt much going on near the mounting holes, but on the component side of the board there are a lot of tracks that run very close to it. These are actually the address bus for the Z80, connecting it via a long path round the board edge to the lower inner connector to the ROM board and on to the sound EPROM. If the board has been dropped or bashed its possible that there tracks are cracked, on in extreme cases totally broken, the board I just repaired had a corner snapped off which had taken 3 tracks with it. If the address bus is broken then the Z80 will just crash, once the tracks were repaired my Golden Axe had sound again. I assume your board actually has its sound ROM in place, there are a lot of empty sockets on a Golden Axe by the way.

3) The amp itself, take off any rings or watches and when the board is on push your finger hard into the pins under the amp chip, do this while ramping the volume control up and down, you should hear faint crackles and hiss from the speaker which should get louder and quieter with the volume control. If you do get this then it proves the amp and the volume control is ok, if you dont then its possible you have a bad amp chip, or a worn out volume pot.
 
Womble--wow, great information! Thank you.

I took a couple pictures of the board I had and tried to compare it with a couple other pictures. One difference I see with my board is c37 is populated on my board and not on the other photos that I have seen. Is this a problem?

The z80b is correct. It wasn't marked with the "b", but when I looked up the number it said it was 6.17 MHz. The crystal is in place, and there appears to be no damage to the corners of the pcb. I will try and check the amp tomorrow.

Thanks again for the help.
Theron
 

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This is where an oscilloscope or a logic probe with audio capabilities comes in handy. You can "see" the sound on the scope and you can "hear" it on the logic probe as it comes out of the digital part of the sound subsystem and makes the first step into the analog section.

By doing that you can immediately isolate where the problem is and further troubleshoot from there.

ekeeb's son, Raiden_2112, got to hear that logic probe with audio when I was repairing a Neo Geo 1-slot for him yesterday. :D It immediately isolated it to the analog audio section and I found a busted cap. Since that board could do stereo audio I replaced the mate to it too.

It sure sounds funky, but works well as a troubleshooting tool.

RJ
 
Thanks for the help. I just recently got a probe and scope. How can I break down the different sections for the audio? Any help would be appreciated.

Thanks,
Theron
 
Weeeell if you have a scope then a whole world of options opens up to you.

Of course you should always start by checking that the amp is actually getting 12V to start with, its the only component on the board using the 12V feed so the lack of sound would be the only impact from losing the 12V. Then move on to an eyeball check of the amp and sound subsystem area of the board, look for pins bent on the underside of the board, these can short out proximal components. Look for missing components, especially capacitors as these often stand fairly proud of the board and are often bashed about. Look for scratches that may have cut the tracks and any signs of damage. If chips are socketted then pulling them out and reseating can fix bad connections due to oxidisation of pins. While the chip is out its wise to look for rust in the chip sockets, double check for bent pins on the chip and make sure you dont cause any when putting the chip back.

After the sanity check you can start from either end and work inwards.

1) From the Amp

Find out what the Amplifier chip is and google the datasheet, this will give you the pinout so you can then find which is the audio input pin. Poke your scope at that and you should see the audio signal if its there - bear in mind that the dipswitch settings on the board may well set it to be quiet in attract mode so you may have to coin it up and start a game to see anything. You can also see if there is anything on the output pin which is helpful if you have a cabling issue, not unheard of with games needing jamma harnesses.

If you have a signal but no sound it will be one of the following

a) Bad amp chip
b) Dried out electroyltics in the amp section.
c) Smashed or missing capacitors in the amp section.
d) Faulty volume control pot.

If you have no input signal then you need to work back through the circuit to the DACs, usually small 8 pin chips, find out what DACs are on board and pull up their datasheets. You will need to check their inputs with the scope to see if they are getting any work to do, if they are and the outputs are silent then you need to see if the chip is actually enabled, the datasheet should help you there. If you get to that point and the DACs have no input I usually find its worth cutting your losses and starting at the other end.

2) From the CPU

Actually I always hit the CPU clock pin before I do any of the above but anyway...

Start at the clock pin, which on a Z80 is pin 6, you should see a regular string of pulses on this pin, a CPU with no clock will do absolutely nothing. If you have no clock then thats likely to be the fault, if you have a clock then you move on.

Second to hit is the Reset and Halt pins (26 and 18 respectively), these are active low pins and usually drawn as RESET or HALT with a line drawn above them to denote "active low". As reset will be active when the pin is low you will need the pin to be high for the CPU to even run, if its low then you need to find out why, if its pulsing then the board is trying to kick start the CPU as it had detected the CPU is doing nothing, this is the watchdog circuit, some boards have it and some don't, Golden Axe doesnt from memory. Halt is an input and output pin, it needs to be Low or the CPU will just stop. Its usually used to stop the CPU in the event of a bus error, tho the CPU can halt the board as a result of software I think.

Next with the scope is to hit up the address lines, A0 to A15...

771px-Z80_pinout.svg.png


...if the CPU is running you should see activity on these lines, any lines that are doing nothing can indicate a fault, either with the CPU or the bus it is trying to drive. Bear in mind that not all address lines may be used by the program running, so if you have an upper few lines doing nothing that may not be a problem, ie if A0 to A12 are active and A13-A15 silent that can be normal. However there should be no holes, so A0-A7 ok, A8-A10 silent and A11-A15 active is almost certainly a fault. If you see this and the CPU is socketted then its just simplest to pull the chip and test it elsewhere, or drop in another CPU and try again.

If you are feeling brave you can test you have connectivity between the CPU, the RAMs and the ROMs on all address lines although there are some caviates about how things are wired up that may this difficult to describe, ie TTL logic may well form part of the addressing system so its highly board specific.

If thats OK then you go on to the data lines, these are bidirectional pins, data outbound to the RAM and data inbound from the RAM/ROM. Its work looking at the state of the signals if they are a blocky mess (if they look like a city skyline) it can indicate bad RAM, also you should have all the datalines on the CPU active, you are highly unlikely to see any missing lines on a RAM that is connected directly to the CPU.

That should get you started!

Never let it be said that I give short answers ;)
 
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Thanks again for the great information. I will need to take some time and digest the info. I really appreciate the help!

Theron
 
Also, make note that if the reset line on a Z80 CPU doesn't go momentarily low then up to high on start up then it won't run.

In other words, if you don't see ANY activity at all on the Z80 then immediately put your logic probe on the reset pin and power cycle the game to see if the low to high transition is occuring.
 
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