Mrs. Pacman help

[P-feif]

O.k. Got the Video Ram Addresser figured out. Problem solved but now I need to get this thing to go into the set up screen. Can get the set up screen to work because there is an issue with the test switch. Anyone have a wife schemattic for it. I have the original manual for Mrs. Pac Man and it has all the schmatics in it however I can't find anythin about the test switch. Also inside the coin door there is a red button just above the test switch. I have no idea what the red button is for. Anyone??



Edit: O.k. looking at the schematic I finally found the test switch. There are some cut wires on the coin door and the slam switch is missing. I'll have to look into it when I get some time. Still don't know what the red button is for.

[P-feif]

Did some poking around on line. Credit button. Seems neither are working. I think when I get home I'll pull the coin door and take a closer look at the harness. The harness from the connector into the cabinet looks intact so I think (I hope) all the wire butchering is right at the coin door.

[P-feif]

GOT IT! I cut all the tie wraps off of the coin door harness and started tracing wires and comparing the harness to the schematic. All of a sudden the schematic made sence and I found the problem. The wires from the test switch are routed through the slam switch, which is missing. I found the ends of the wires and according to the schematic there is a red wire on one of the coin mechs that acts as a common ground that come off of one side of the slam switch. On the other side of the slam switch is a blue wire that goes up to the test switch. When the test switch is in the test position power should go through the blue wire then the slam switch and then the red ground on the coin mech. I tied the blue wire to the red ground on the coin mech and WA-LA I had access to the set up menu.

Now if I can just figure out how to get it to boot to Mrs. PacMan instead of the game menu I'll be all set (might no be a possibility, got an e-mail sent to Slava to ask if it can be done).

We'll see, If I don't like the 4 in 1 kit I can always convert it back to Mrs. Pacman again. I used a sharpie to mark everything on the PCB so I can put it back the way it was if I ever want to.

[P-feif]

I'm have a problem with a distortion in the sound. I've looking over the diagram/schematic and found some capacitor that I thought I'd change via the shotgun approach. One of them is a tantalum capacitor. When looking at the board more closely I found a trace on the back of the board that bridges the tantalum capacitor to one leg of a nearby chip and the trace has been scratched off. I'm wondering if this might be the issue??? Should I bridge the two pins with some solder to repair the trace? Can some of you with more skill then me please weigh in? Here's some pictures of the board/cap/trace/schematic. Pen is used as a pointer.



Cap at C49 front of board


Scratched off trace on the back of the board. The pin to the right of the pointer is one leg of the cap, pin to the left of the pointer is one leg of a chip. I believe it is on the schematic as a gate called 11A (Note 11A is listed twice on the schematic).

[VertexGuy]

I wouldn't be able to see that scratch, the board would be at Eldorado by then .
Connect them... it don't work... scratch it back off.

[P-feif]

Thanks I'll try it.

Also I have a replacement cap for it but nothing on the board or old cap indicates + or -. Any idea which way it goes.

[P-feif]

O.k. I bridged that trace. Made no difference at all. Upon inspecting the board a little closer I found that on the parts side there is another trace that connects those two pins. So I really starred at the schematic and figured put which is + and - for that tantalum cap and I replaced it. Still no change. The sound issue is as if the sound is breaking up at times. You can really hear it during the intermission when it plays some music. The more base sounds really make it act up. The more high pitch sounds it almost doesn't act up at all.

Next to the tantalum cap is a mylar cap. I bought a replacement for it but it's huge and I don't think it will fit on the board very well so I'm not going to use it. Also there is a great big heat sink covering these two caps. It was very hard for me to replace the tantalum cap. I bent the heat sink out of the way somewhat being careful not to crack to solder that hold it because it also hold a chip in that location too (the same chip the I "think" has the 11A gates). Since everything on this board is soldered on both sides trying to get the solder out of the holes with that heat sink in the way was a real chore. In the end I inadvertently bridged the two pads on the parts side and could not get my solder sucker to remove it all, even after adding a little solder to give it something to suck up. I ended up using the solder sucker to remove what I could and then I carefully used a sharp pointy tool to scrape a little gap down the center of the two legs/pads.

Just played a quick game and it still sounds the same. I know it's not a ROM issue because I removed all the ROM's and replaced them with a 4 in 1 kit from Souza on-line. I had the same problem with the original ROM's and still have it with the 4 in 1 kit. There is something going on with this board, I just can't figure it out.... yet.

Any idea's guys?

[P-feif]

Still trying to trace down the sound distortion issue. I've replaced an electrolytic cap (that doesn't come in the Bob Roberts axial cap kit) and a tantalum cap, plus about 5 or 6 resisters trying the shotgun approach. Still have not fixed it. I did buy a crystal for it, not for this problem but only because it was $1 and I thought I'd just hang on to it. Looking at the schematic I don't see any real big interaction between the crystal and audio processor but I'm wondering just what the crystal is used for? I remember playing around with my friends RC cars when I was a kid and I remember using crystals to control the output frequency of the transmitter/controller and you also had to have a matching crystal in the receiver. So what does this board need to use a frequency for?? Part of the clock? It seems to directly interact with the Z80. If any of you know please if you could explain it.

(I did plug an old car speaking into this thing to see how it sounded, the Ms. Pacman audio amp did not have enough power to really drive the car speaker so it sounded really tinny but you could hear the same distorted sound as with the original game speaker so I don't think my speaker is bad)

[iankellogg]

well to start with, the crystal is the main clock for the entire board. there is no audio processor per say in pacman. How it works is the z80 tells the audio chip to play a certain sample. the audio chip is kind of like a eprom with a clocked output. the output goes through a R-2R ladder dac to generate the analogue signal of the sound. It goes through the amp and out to the speaker. I don't know what kind of distortion you are talking about so I can't say for sure whats the problem but audio is both simple to work on a pain to fix.

[P-feif]

Thanks Ian. Well the board runs fine so I'm guessing the crystal is fine.

Maybe I should fineally make a youtube account so I can post a video and let you hear it.

Basically the sound sort of brakes up. I don't know it just doesn't sound right and the only way for anyone to understand it would be for me to post a vid. Can you guys see the vids that I've posted off of Facebook?

[iankellogg]

If the video is set to public we can

[P-feif]

O.k. Then I'll try to post something that demonstrates the sounds issue when I get home from work tonight.

[P-feif]

O.k. here's the video. You can hear how the sound is just not right. Sometimes you can hear the base sounds break up really badly but not so much in this particular video. Also this machine was doing this when I first bought it and through all the repairs that I've done nothing has changed the sound issues one bit. Note that I have installed a Souza 4 in 1 kit, the sound issue was there with the original rom chips and is still there with the Souza kit. I have also changed the tantalum cap at C49, the Electrolytic cap at C48, the resistors at R5, Rk96, R95, R94, R93, and R92. I have the ceramic caps for C46 and C47, and a mylar cap for C50 although I have not installed them (yet). I have not tried to change any of the IC's yet mostly because I don't have a logic probe and am not sure how to check them although I could just change them all via the shotgun approach. Also I have install a high score save kit (Souza), I did a full axial cap kit from Bob Roberts and also installed an edge connector repair kit from Bob Roberts along with a wire harness edge connector also from Bob Roberts, along with the 4 fuse, fuse block on the bottom of the cabinet. I'm also not opposed to the idea that this could simply be a bad speaker. 



https://www.facebook.com/video.php?v=10203943503564992&l=8181059334743831816

Sorry I could not figure out how to post the video with tags on the link so I hope the link works. If anyone would like to show me how to post the video I'm more then willing to try to learn it.

[iankellogg]

I think it might be a bad speaker. Try turning the volume down as well, see if that helps. If you replaced C51 and C48 you should be fine with the board.

[P-feif]

Alright well I did find a speaker on Mike's arcade web site for a good price so I guess it can't hurt to buy it. If it doesn't work then I'll let you know. Thanks Ian.