Sys 80 Non CPU boot/IRQ issue

[ddstoys]

DID you do the slam switch Mod Marty?   It wont boot without this done? 

[Marty Machine]

I'm not sure about a 'mod' but the label on Z26 input says "slam switch"...

[Marty Machine]

Marty, check my post on CRO's...i reckon this will be your next test-gear purchase 

http://aussiepinball.com/index.php?topic=1686.0

MM.

[ddstoys]

Here is the link to the slam switch mod with the board not connected to the machine it thinks the slam switch on the front door is open so it wont boot...          http://www.pinrepair.com/sys80/index1.htm#slam

[Marty Machine]

Ahhh, might be just what MartyJ needs to know....nice !

[MartyJ]

Thanks for help guys,

Yep, slam mod done

MM,

No playfield attached at present.  Just backboard and power section.  AFAIK this is fine, power supply rebuilt and connected to CPU.  Without displays attached (shouldn't matter) can still monitor if CPU booting by probe on pin 4 U1.

Clock seems to be fine.  On my cheapo logic probe, I'm getting 1 (high) 0 (low) and pulse all lit which I believe is pulse.  This is on Z3 pin 6 and U1, U4,U5,U6 pin 39.
U2/U3 are new.  I dont know where to read the clock on these and couldn't see on schematic.

From the pinrepair guide, the clock looks to be OK, same as RDY and Reset.  Something is holding the IRQ high.  I have not touched or looked at Z9/Z10 or Z7/Z8.  These are about the only ones I havn't replaced.  From the schematics (Z9) there should only be activity on 4,5,6,7 & 14 (gnd).

[MartyJ]

Pin 34 on U5 held high.

Pin 15 U5 held low

Pin 12 Z26 held high

[Marty Machine]

U2/U3 proms don't need clocks.

I'd monitor cpu pin40 (reset) which will toggle during bootup. (proves cpu is booting).
if pin40 is stuck, this is also feeding the 3 PIA's they might all be held in reset mode....

Z7,8,9,10 are all to do with prom/address decoding for various size proms....shouldn't be a problem, as your problem seems to be earlier than all that....

[Marty Machine]

Pin 34 on U5 held high.

Correct !

Pin 15 U5 held low
Pin 12 Z26 held high

Is the mod in between these 2 pins? they should both be low on the schematic...

[MartyJ]

Pin 34 on U5 held high.

Correct !

Pin 15 U5 held low
Pin 12 Z26 held high

Is the mod in between these 2 pins? they should both be low on the schematic...

AFAIK the mod doesn't touch U5.  Pin 13 is the only one which buzzs out to where the mod is.....

Pin 40 on U1, with DMM 0.0 then jumps to around 4.5 to 4.8v and holds there.

[Marty Machine]

Pin 15 U5 held low
Pin 12 Z26 held high

AFAIK the mod doesn't touch U5.  Pin 13 is the only one which buzzs out to where the mod is.....
Pin 40 on U1, with DMM 0.0 then jumps to around 4.5 to 4.8v and holds there.

Pin 40 should ALWAYS be 5V (or near enough) which means the cpu is NOT in reset, that's cool.

Re-Check :

Pin 15 U5 held low
Pin 12 Z26 held high.

The schematic shows they directly connect, if one is high so will the other, yet you see 2 different levels?

maybe a cracked track in between these 2 pins??

[MartyJ]

Hmm,

Definately NO continuity between pin 12 Z26 and pin 15 U5.  Might be an error in schematics as the track from pin 15 u5 pin 10 Z12.

[The pinballist formally known as Dean Morgan]

Hmm,

Definately NO continuity between pin 12 Z26 and pin 15 U5.  Might be an error in schematics as the track from pin 15 u5 pin 10 Z12.

Marty,

Just checked on two (2) spare boards I have and Pin 15 of U5 goes to Pin 12 of Z26 on both.  One was a System 80a and the other system 80b.  This is as per the schematic.  You sure your looking at the correct ICs.  U5 is the middle of the three 40 pin 6532s abd Z26 is the bottom right hand IC.

[Marty Machine]

Definately NO continuity between pin 12 Z26 and pin 15 U5.  Might be an error in schematics as the track from pin 15 u5 pin 10 Z12.

Very weird, as the schematic shows Z12-pin10 goes to Prom 2 addressing, pin21, via the E2 jumper link....
 
MM.

[MartyJ]

Definately NO continuity between pin 12 Z26 and pin 15 U5.  Might be an error in schematics as the track from pin 15 u5 pin 10 Z12.

Very weird, as the schematic shows Z12-pin10 goes to Prom 2 addressing, pin21, via the E2 jumper link....
 
MM.

Sorry guys, tested again.  Wrong pin.
Trouble counting this morning   
Continuity OK pin 15 U5 to pin 12 Z26.
U5 pin 15 is high
Z26 pin 12 is high