Defender - Self Credits!?

jetusenet

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Hi;
I almost have my Defender completely repaired - ALMOST!

It does a very strange thing, sometimes, not all the time, it will add credits by itself! Either the game could be just sitting there or during game play but you will hear the credits adding up. I watched it and it will add 4 credits every 3 seconds, exactly every 3 seconds.

I probed IC24 (4049) on the ROM PCB pins 4,6 and 10 when this is occurring and that is not the cause of the credits.

I probed IC22 (PIA) and pins 29,30 and 31 are always pulsing - is this correct? As I am new to this level of troubleshooting, I really do not know what to expect.

Thanks in advance
Jeff
 
Hi;
I went over the schems and it appears that the coin door runs through the ROM board and through that, onto the CPU PCB. I did trace the coin mechs through IC24 and received a high signal when tripped but I am receiving confusing results through the PIA and since I am not proficient with the "probe", I am not sure if the results I am receiving are appropriate or not.
Jeff
 
The coin switches run through the PIA on the ROM card. Reflowing the widget connectors while occassionally useful would have no effect.

ken
 
Hi;
I almost have my Defender completely repaired - ALMOST!

It does a very strange thing, sometimes, not all the time, it will add credits by itself! Either the game could be just sitting there or during game play but you will hear the credits adding up. I watched it and it will add 4 credits every 3 seconds, exactly every 3 seconds.

I probed IC24 (4049) on the ROM PCB pins 4,6 and 10 when this is occurring and that is not the cause of the credits.

I probed IC22 (PIA) and pins 29,30 and 31 are always pulsing - is this correct? As I am new to this level of troubleshooting, I really do not know what to expect.

Thanks in advance
Jeff

Try and isolate where the problem is.

Disconnect your coin door and see if it's still happening.

Check your voltages (when it's happening)
 
Ken;
I proved IC24 good then went onto IC22. I tried to probe the PIA but receive pulsing on pins 4, 5 and 6, even when not crediting the machine. Is this the correct output or I am I looking at the wrong pins?!
Thanks
Jeff
 
Ken;
I proved IC24 good then went onto IC22. I tried to probe the PIA but receive pulsing on pins 4, 5 and 6, even when not crediting the machine. Is this the correct output or I am I looking at the wrong pins?!
Thanks
Jeff

Looking at the schematics, the Coin switches are hooked up on IC22 at:

PA2
PA4
PA5

Those are fed from IC24 from pins 12, 15 and 2. The inputs to those pins should be 11, 14, and 3.

2J3-3 -> 11-IC24-12 -> IC22-4
2J3-5 -> 14-IC24-15 -> IC22-6
2J3-6 -> 3-IC24-2 -> IC22-7

Check the inputs to see if they are High, Low or Pulsing. Those pins should only change state when you press the credit switch. The output should be the inverse of what the input is. If the input is Low, the Output should be High.

If IC24 checks out, it's probably IC22.
 
Hi;

Here is what my set of schems show:

2J3-3 -> 5-IC24-4 -> 4-IC22
2J3-5 -> 7-IC24-6 -> 6-IC22
2J3-6 -> 9-IC24-10 -> 7-IC22

I am pretty sure that my testing procedure has proven IC24 good so that leaves IC22 as the next in line. When I probed IC22 4,6 and 7, they appeared to be always pulsing, would this be normal?

Thanks
Jeff
 
Hi;

Here is what my set of schems show:

2J3-3 -> 5-IC24-4 -> 4-IC22
2J3-5 -> 7-IC24-6 -> 6-IC22
2J3-6 -> 9-IC24-10 -> 7-IC22

I am pretty sure that my testing procedure has proven IC24 good so that leaves IC22 as the next in line. When I probed IC22 4,6 and 7, they appeared to be always pulsing, would this be normal?

Thanks
Jeff

You might be looking at a different version of the schematics then I am.

Here is what I see:

defender coin switches.png
 
Jeff,

Do you have the original Defender (also known as the "early" Defender) or the later board. http://www.robotron-2084.co.uk/techwilliamshardwareid.html#defender can show the differences.

Based on your earlier comment about having the early sound card, you may have the early set. There are some slight differences between the early and later boards. I don't know if they are expressed in the ROM card or not. I know the drawing sets are different.

ken
 
I probed IC24 (4049) on the ROM PCB pins 4,6 and 10 when this is occurring and that is not the cause of the credits.

I probed IC22 (PIA) and pins 29,30 and 31 are always pulsing - is this correct? As I am new to this level of troubleshooting, I really do not know what to expect.

Thanks in advance
Jeff

The three coin switches are pins 4 (PA2), 6 (PA4) and 7 (PA5) on the PIA (chip IC22). These would be pins 11/12, 15/14 and 2/3 on IC24.

Pins 29, 30 and 31 are data address lines and I would expect that they will be pulsing.

Pins 4, 6 & 10 on IC24 correspond to input pins 5, 3 and 2 on IC22 which
are the PA3 (High Score switch), PA1 (Advance switch) and PA0 (Auto Up switch) inputs

ken
 
I have a similar set of drawings, in fact, I am looking at what looks the same drawing except for the pin designations. So now I habe to figure out which version I have!!!!!

I did test pin 4 of IC24 while flipping the credit switch and I did receive a "high/low" signal so that one is correct. I will have to go back to the board now and trace the wires to prove the path. But first I have to shovel, we had another snow storm last night and I got back from work late because they held us until the "emergency" had passed.

Thank you for your assistance + help and I will post my results tonight.

Jeff
 
Done shoveling - was not so bad this time!

I have been thinking and since I proved pin 4 out of IC24, then I have the correct schems for my ROM board, otherwise it would not have changes state when I toggled the right credit switch.

Now, since the outputs of the PIA are always pulsing, how can I tell if the PIA is bad??

Thanks again
Jeff
 
I guess I'll just swap out the PIA and see if that takes care of the "self credit" issue but I really would like to know how to actually test the outputs of the PIA for the future....
Thanks
Jeff
 
How would one trace the outputs through the PIA to prove it bad or good??

Can I use the probe or do I need "heavier" equipment?

Thanks
Jeff
 
I really wish I knew wtf you were talking about LOL

never mucked with a probe before. probably going to be something I'll need when I start working on my Defender though.

I don't entirely understand what people were saying when they told me to jumper that one chip on the sound board to make it play individual sounds. surely you don't do that with wire, do you??
 
I am trying to find out what (where) the outputs of the PIA would look like to show that the IC is functioning properly,during a test credit trip or during actual normal operation.

I think what you are talking about is when you ground the inputs to invoke the sounds on the sound PCB.

Jeff
 
I am trying to find out what (where) the outputs of the PIA would look like to show that the IC is functioning properly,during a test credit trip or during actual normal operation.

I think what you are talking about is when you ground the inputs to invoke the sounds on the sound PCB.

Jeff

You should probably carefully desolder the current PIA, socket it and try a new one.
 
I really wish I knew wtf you were talking about LOL

LMAO -- Great post in the middle of a technical discussion! Yes, if you are jumpering, then you are bypassing other wires or circuitry that may be bad to elicit a desired outcome from the game. Depending on what you are trying to bypass, touching a wire from the ouptput of one chip or from +5V or ground to the input of another chip or button is how it is done. Jumpering on a board is fairly safe (for you, not necessarily the board...) - only 5 to 12 volts. But, trying the same technique on a TV or arcade monitor may be hazardous to your health.
 
Now I'm really upset!

I replaced the PIA on the ROM board, (even though I could not prove it bad) and now it's doing it even more!

Every so often, during initial boot, (cold) I might get a ROM error but then it goes away. This does not happen every time and in fact I had forgotten about it until now as it just happened again, then went away - again. I placed the game in test and of course, all ROMs are good. Could a bad ROM, (intermittently bad) cause this "credit" problem??

This is driving me CRAZY!!!!!!

Jeff
 
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