(Topic ID: 104637)

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

By action76

9 years ago


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  • 26 posts
  • 5 Pinsiders participating
  • Latest reply 3 months ago by action76
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#1 9 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

#3 9 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.

#6 9 years ago

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

1 week later
#9 9 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 9 years ago

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

#14 9 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.

#18 9 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?

#20 9 years ago

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

#22 9 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!

9 years later
#26 3 months ago

LOL! Glad to see a 9 year old post is still helpful. Glad you got it back working again.

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