Defender repair help.

[andykmv]

while youre in a frequency testing mood, check the horizontal and vertical video sync signals, and the Count 240 signal (defender schematic, page 5 sheet 1 of 2 mpu schematic, bottom rhs) on the mpu board.

is the monitor signal cabling at the monitor wired for composite sync or separate horizontal and vertical sync ?

 

[AMG]

well..... now what. I'm out of ideas of what the problem could be.

Grab the 2 Defender troubleshooting guides here:
http://www.vidpin.com/tech_videorecap.asp

One is designed for a logic probe, the other for an oscilloscope, but both can give you ideas about what might be wrong. It's also handy to have the theory of operation manual for more detail on a particular circuit, and a decent schematic.

 

[AMG]

And there are some decent schematics and other docs at the bottom of this page:
http://www.cityofberwyn.com/schematics/

I had those but couldn't remember where I found them, thanks to mecha187 for posting the link in another thread.

 

[DarkWolf896]

just a quick thought. after inspecting the board closer, I realized the 7474 chips I removed were SN 7474N and the new ones I used are just 7474 is there a difference??

 

[andykmv]

just a quick thought. after inspecting the board closer, I realized the 7474 chips I removed were SN 7474N and the new ones I used are just 7474 is there a difference??

minor if any. nuttin to worry about..

 

[Riptor]

just a quick thought. after inspecting the board closer, I realized the 7474 chips I removed were SN 7474N and the new ones I used are just 7474 is there a difference??

Nope, just a package code. N=plastic dip
The prefix is the manufactuer. SN =Texas Instruments

 

[DarkWolf896]

ok, just trying to rule any possible causes of the problem.

EDIT: I ordered a logic probe, I'll do a run through of the troubleshooting guide when it arrives.

 

[DarkWolf896]

ok, I've probed the board. 2I pin 37 low plused for 1 sec then high like it should.
but 6R pin 6,8,9 dont pulse. I replaced the chip again. 7J pin5 and 7L pin 9 dont pulse.
and 5P pin 6 doesn't pulse. 4C pin 8 does. and so does 1F PIN 3,5,9,11,13 as defined in the video recap flowchart. ??

 

[andykmv]

....6R pin 6,8,9 dont pulse. I replaced the chip again.

after u replaced 6R again, were u getting the expected pulses ?

use logic probe and put on 6R pin 11 and tell us what you get.

if you have a multimeter with a frequency (Hz) measurement section:
- put the +ve lead onto 6R pin 11 (-ve to gnd), tell us what you get. - this is the inverted output of the main 12mhz system clock
- if your DMM overranges (ie cant display such a high clock freq.), put the probes on 6R pin 8 (and -ve the gnd) and tell us what u get. this is the 4MHz clock used by the video circuit. most DMMs should display this one.
- also check your E and Q clocks at pins 34,35 and tell us what you get. should be 1MHz. these are the system clocks that are derived from the 4MHz clock that is derived from the 12MHz main system clock.
- put the probes on 6R pin 8 (and -ve the gnd) and tell us what u get. this is the 6MHz clock also used by the video circuit. this is derieved from the 12MHz clock.

in short if 6R is not outputting clocks , the system she no work and video output wont work.

 

[DarkWolf896]

after u replaced 6R again, were u getting the expected pulses ?

use logic probe and put on 6R pin 11 and tell us what you get.

if you have a multimeter with a frequency (Hz) measurement section:
- put the +ve lead onto 6R pin 11 (-ve to gnd), tell us what you get. - this is the inverted output of the main 12mhz system clock
- if your DMM overranges (ie cant display such a high clock freq.), put the probes on 6R pin 8 (and -ve the gnd) and tell us what u get. this is the 4MHz clock used by the video circuit. most DMMs should display this one.
- also check your E and Q clocks at pins 34,35 and tell us what you get. should be 1MHz. these are the system clocks that are derived from the 4MHz clock that is derived from the 12MHz main system clock.
- put the probes on 6R pin 8 (and -ve the gnd) and tell us what u get. this is the 6MHz clock also used by the video circuit. this is derieved from the 12MHz clock.

in short if 6R is not outputting clocks , the system she no work and video output wont work.

6R pin 11 is OF(over frequency)/6R pin 8 is 4mHz/the E and Q are 1mHz.
and you said that 6R pin 8 is the 4mHz clock and the 6mHz.???

 

[Scucci]

Sorry if I'm coming in late.

Looks like decoder issues/monitor issues.

The black bands in the monitor are probably just it needing some adjustments.

The grey screen is USUALLY decoders (every time I've see it, bunches, it's the decoders).

I'd get a full set of EPROMs/Decoders burned and chunk the rotting ones, but that's just me.

Maybe replace all the sockets as well, ribbon cables, clean the connectors on the power supply/boards (what I'd consider basics for Williams' machines). Then you know you're playing with good parts/connections.

But, again... I'll toss my hat in and say it's the decoders.

 

[andykmv]

6R pin 11 is OF(over frequency)/6R pin 8 is 4mHz/the E and Q are 1mHz.
and you said that 6R pin 8 is the 4mHz clock and the 6mHz.???

E&Q good!, 6rpin8 is good at 4mhz, this means 6r is working well. oops pin 6 is the 6mhz clock - testing that should yield OF as well.

 

[andykmv]

7L pin 9 dont pulse.

Check pin 11 with the DMM frequency tester. should be 4MHz

7J pin5 dont pulse.

'
Check pin 5with the DMM frequency tester. should be 1MHz. this is the q clock

and 5P pin 6 doesn't pulse.

is pin 6 steady high or low ?
check the logic state of pins 4 & 5 of 5p. are either of those steady high ? either of them pulsing ?