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(Topic ID: 104637)

TECH - System 9 - Sorcerer won't boot - error 7 on mpu display


By action76

6 years ago



Topic Stats

  • 24 posts
  • 4 Pinsiders participating
  • Latest reply 6 years ago by KloggMonkey
  • Topic is favorited by 6 Pinsiders

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SN74365A-pinout.jpg

#1 6 years ago

I picked up a Sorcerer the other day and have been trying to get it up and running. When turned on the seven segment display on the MPU board immediately shows a 7. The previous owner said everything was working fine and when he turned it on one day it did that. I have isolated the MPU on the workbench and powered it with a PC power supply and the results are the same - the seven comes up instantly. I would assume then, it is an MPU problem and not a power problem. I also reseated all the chips and tested the continuity of the legs through the board to eliminate bad sockets. I am trying now to follow some troubleshooting from Clay's guides but cannot find the test points he is referencing. He says TP1 is to the left of the batteries and TP2 is next to U21 (which I believe is the crystal) but I don't see either TP. Does anyone have a picture pointing out these TPs? Also does anyone have any suggestions on what the issue may be or where I should look next?

Thanks

#2 6 years ago

I would refer to the PinWiki article about Williams System 9 troubleshooting.
A lot of good hints in there.

http://www.pinwiki.com/wiki/index.php?title=Williams_System_9_-_11

#3 6 years ago

Thanks, but unless I've missed something there is not much if anything in there addressing my particular problem and nothing that tells me where those test points are on the MPU board.

#4 6 years ago

Hey Action76,

This will help you out: http://www.pinwiki.com/wiki/index.php?title=Leon_Borre_WMS_System_9_Repair

It applies to using Leon's test rom, but skip the part about using his rom and read the part about testing the points on the CPUs for the clock, VMA, E signal & IRQ, as well as voltage measurements on the CPUs with no EPROMs installed.

There is not a whole lot of repair information on system 9 MPUs out there because they are so similar to System 11 boards, so it makes debugging them a bit trickier if you haven't worked on one before. They are mostly the same, so the tips that apply to testing and repairing system 11 boards often apply to system 9. I'm in the same boat as you with a board that is stuck with a "7". I've replaced almost all of the logic so far, CPUs, EPROMs, RAM, decoders, fixed bad traces, you name it. Buzzed it out a number of times. Still working on it.

#5 6 years ago

One area I would check out if it was working then suddenly pooped out would be the tri-state buffers for the data lines. If a buffer fails, it'll definitely put a 7 on the board. Those are U1-3 I believe, directly underneath the main CPU (not the audio cpu).

#6 6 years ago

OK thanks. How exactly do you check the tri-state buffers?

#7 6 years ago

Put your meter on diode check. You can test for shorts on all logic ICs this way as well. Place one probe on a gnd pin (pin 8), and individually probe all of the other pins. Each should read .6v or inf, with the exception of the power rail and any IC pins that are tied to gnd. If you get 0 ohms and that pin is not tied to gnd, then that gate is shorted.

They're labeled 8t97 on the schematic/part layout, but can be replaced with 74365 logic ICs (not 74ls365 or 74hc365. You can use 74hct365 I believe though if you can't find SN74365's).

SN74365A-pinout.jpg

#8 6 years ago

Here is a better diagram of the IC, clearly showing the inputs, outputs, and the enable pins (NOR gate).

images.jpg

This is helpful to for understanding logic ICs.

http://en.wikipedia.org/wiki/Logic_gate

It is really simple how they work, and when things fail with boot-up and power rails and ground and traces check out okay, it usually means that logic ICs have failed and are not shifting bits around like they should be. Bad PIAs can also cause boot issues though, which is why Leon's test rom is helpful if swapping out logic doesn't solve your issue.

1 week later
#9 6 years ago

In my testing I have found that (I think) the reset section isn't working. I have tried to ground pin 40 of the CPU to see if it would come up but that did nothing. I know at power on, pin 40 is supposed to start low for about a half second and then go high and stay high. This one starts low and never goes high. so I never get 5 volts at the CPU. Where should I be looking for the cause of this? Also can you jump 5 volts to the circuit to see if it will boot or is that a no no?

#10 6 years ago

FYI - I changed the cap at C9 with no result.

#11 6 years ago

Always a good idea to change those smaller electrolytic caps on the board anyway.

How are you powering the board? Are you using a bench power supply, or the game's power supply?

If you are only using +5v and GND, you need to run a jumper from the +5v supply to the anode of ZR1 for the reset section to function properly. You also need a beefy +5v supply for this method. I think these boards require a minimum of like 1.5A to work properly.

If you are plugging in the power connector from the game's power supply, then you don't need to jumper it to +5v (and shouldn't or you'll burn stuff up - been there, done that), as the Zener will be powered with +12v on the opposite end like it would be normally for the reset circuit to function properly.

Your RAM could be bad if it is stuck, or you may have other issues preventing it from booting and the reset circuit starting, such as the IRQ, E-Signal, or VMA or address lines. Have to tried hitting the reset switch on the side to see if it switches states from 7 to 0? Also check continuity between your CPU and EPROMs/RAM.

Have you check voltages on the CPU with the test ROM pulled under "worst case scenario"?

#12 6 years ago

Also, don't jump +5v to pin 40. You can temporarily ground pin 40 and see if it resets though.

#13 6 years ago

I recommend off board power supply to isolate from the game PSU. If you have a computer PSU laying around, that will work great.

#14 6 years ago

I have got the board on the bench using a PC power supply. I have tried powering the board by jumping +5v to the anode side of ZR1 and by running the +12v from the PSU to the IJ7 connector (but not both). When you say reset switch, do you mean one of the two diagnostic switches on the board? I have pushed both of them and nothing happens.

I believe I have checked the voltages with the test ROM pulled but I will do it again just to make sure. I will also check the continuity between the CPU and EPROM/RAM and get back with you.

#15 6 years ago
Quoted from action76:

When you say reset switch, do you mean one of the two diagnostic switches on the board?
I believe I have checked the voltages with the test ROM pulled but I will do it again just to make sure. I will also check the continuity between the CPU and EPROM/RAM and get back with you.

Correct, the diagnostic switches. As long as you have confirmed your CPU is working (with the test rom pulled), with Leon's test rom in place:

"pins 2, 6 and 40, which have to be positive (around 4 volts). On pin 39 is a clock signal, on pin 4 IRQ; on pin 5 the VMA signal, and on pin 37 the E signal (synchro for external parts). These all have to be around 2 to 3 volts (measured with a dmm)"

If any of those are off, you need to trace those lines back through the schematic and find out what is causing those voltages to be off. Keep in mind that if the reset circuit is faulty, obviously the IRQ and VMA aren't going to read the correct values because the CPU isn't running, but part of that can be the associated chips in the IRQ network, so it makes it tricky. So you need to get that reset circuit working first. Check the 4401's, the 4403 & resistors in the PS network. Then check the 555 timer and associated components as well.

#17 6 years ago

This is also a huge help: http://gamearchive.askey.org/Pinball/Manufacturers/Williams/pdfs/pinball_troubleshooting_sys9.pdf

Page 36 covers the blanking circuit if you do not have +5v on pin 40. Inspect all components of that circuit. Also suspect PIA U5.

#18 6 years ago
Quoted from thedefog:

"pins 2, 6 and 40, which have to be positive (around 4 volts). On pin 39 is a clock signal, on pin 4 IRQ; on pin 5 the VMA signal, and on pin 37 the E signal (synchro for external parts). These all have to be around 2 to 3 volts (measured with a dmm)"

There is no voltage on pin 40 so I was looking at the blanking circuit. According to Clay's guide

"A way to test the blanking signal is to boot the CPU board with only +5 volts and ground (no +12 volts). This will keep the reset line low, and hence the blanking signal should also be low. If blanking is high there is a problem in the blanking circuit. Check the U23 555 timer chip and Q50 2N4403 transistor - these are the guts to the blanking circuit. The signal itself can be seen at U43 pin 3"

The blanking signal is low and stays low. So I assume the blanking circuit is ok then? So I guess the question is, what is keeping the reset line low?

#19 6 years ago

Those transistors at the top, the 3 4401's that are in a row, check those out. Also check the zener diode. With the +12v connected, the zener should read +12v(or +14v unregulated) on the anode side, and +6.8v on the cathode side.

#20 6 years ago

I believe the three transistors are fine but the Zener diode reads 12 V and 4.6 V

#21 6 years ago

Check the resistors in the area of the +5v section. Something is pulling your +5v down enough to keep it from running.

#22 6 years ago

Woo Hoo! I don't know how I missed this because I swear I checked it before, but R2 was bad. I replaced it and now I have a 0 on the display now! I haven't tried it in the machine yet but it looks good on the bench. Much thanks to thedefog for all the help!

#23 6 years ago

No problem. Good luck with the rest of it. Hopefully not much else is wrong with it. I got mine booting as well finally. A brand new ne555 timer was faulty. I got one of those $20 logic testers off ebay from China and it confirmed it.

#24 6 years ago
Quoted from thedefog:

This is also a huge help: http://gamearchive.askey.org/Pinball/Manufacturers/Williams/pdfs/pinball_troubleshooting_sys9.pdf
Page 36 covers the blanking circuit if you do not have +5v on pin 40. Inspect all components of that circuit. Also suspect PIA U5.

Thanks for posting lots of good info in it.

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