Black Knight Williams Sys 7...

[Pinfan]

Hi Guys,

as the title suggests.

Williams System 7/BK. No displays and no CPU controlled lamps upon power up.

A little bit of history first. Game was playing flawlessly for 1 year
now. Turn it on the other day and BAM ! no go..No indication what so
ever.

If i press the sound board test all sounds work accordinly. Turn on
the machine and nothing but the GI comes on.I have no access to
anything but the sound board.

Marvins site/and alot of the archived RGP posts suggest that it is the blanking signal and surrounding components.

I am NOT getting 5v upon power up at pin 37 on the 40 pin connector
which suggest the blanking signal. ( 0.12 v is what i am getting )

Checked the voltages on the PSB and it has its 5v @ J6 pin 7 and
-100v @ J5 pin 3 and +100v @ J5 pin 4, so its getting the voltage to the MPU
and the displays.

This is what has been done so far to combat the problem but to no
avail.

MPU board has had

40 pin interconnect, both male and female have been replaced.

all fuses checked,double check and triple checked.

All connectors have had solder reflowed.

IC7 ( 7404 ) replaced ( mpu )

IC23 (555 timer ) has been replaced ( mpu )

C 84 cap replaced ( mpu )

Q1 ( 2n4403 ) replaced ( mpu )

5101 has been replaced with a known working one.

All these parts have been recommended by Clay to be changed as they are in the blanking singnal circuit.

Driver Board-

All PIA's have been replaced with known working ones.

IC 13 & IC 14 have been replaced. ( 7408 lamp and column blanking )

Get this I put in a known working driver board out of my Gorgar and
into the BK and still the same, nothing else but the GI's, with the
known working driver board however i get random BK sounds everytime i turn the machine on and off. So a different sound each time.

This to me suggest that it is the MPU which is at fault.

I spent a few hours reading through the google archives and all posts lead me to dead ends !

Are there any chips on the driver board or MPU that send the high signal to or
are in the blanking circuit that i have missed and i should or would need to change ?

Am i going down the wrong path ?

Any help would be appreciated ?

[humpalot]

Is there 5V at the CPU?

If so then,

Might want to read.

http://www.pinrepair.com/sys37/index2.htm#deadcpu

New eproms.

Try out Leon's rom.

Upgrade the Gorgar boards so you can swap them between machines?

[Strangeways]

I have not worked on a system 7, but if anyone here has any tips that might help - I live close by to PinFan and I'm happy to go around and tinker..

[Retropin]

I have a heap of notes from working on sys 7 that i shall dig out.

IF it is the blanking signal then a test to confirm this is to jump the 5v to pin 37 ( from memory), if game boots then, yep blanking signal is at fault.

Blanking HAS to be a nice smooth 5v - any ripple will throw it out.

ill get back later with what ive made note of from previous workings.

The 5V jump test is on Marvins site - check there first as im going from memory here from 6 years ago

[Pinfan]

Thanks to all so far..

Apparently Leon's test rom is useless to a locked MPU... will only help if the board boots or patially boots...

I have read Clays guides over and over and tried numerous things.

One thing i must say i am never happy to jump voltage from where ever just can't bring myself to do it. 

I think i will get you Nino to come around and have a quick squizz... Time permitting of course...

Could it be as simple as replaceing one of the caps Gavin ?

[Retropin]

honestly, there is no harm jumping the 5V, all you are doing is by passing the blanking signal, if game boots, it is the blanking.

Another oddity with the Wms sys is with the 6821 PIA chips. Sometimes these dont just fail automatically. I chased a fault for ages once scratching my head.

Test the output voltages on the CPU PIA's. If you have anything under 4V this is not seen as a logic high and will cause the CPU to lock up. If you find on the outputs any voltage around 3V then replace this PIA.
I chased and chased a fault with a logic probe and came up with nothing. tested with DMM and got 3V on one of the outputs, so then i wondered - is this enough for logic high?

Replaced PIA - got 4V or so and game booted.

Worth a check

[humpalot]

Do you have 5V at the CPU?

[Pinfan]

Do you have 5V at the CPU?

Yep, a very clean 5.05 V.

All test voltages are there and present bar the blanking @ TP4.

[Pinfan]

honestly, there is no harm jumping the 5V, all you are doing is by passing the blanking signal, if game boots, it is the blanking.

Another oddity with the Wms sys is with the 6821 PIA chips. Sometimes these dont just fail automatically. I chased a fault for ages once scratching my head.

Test the output voltages on the CPU PIA's. If you have anything under 4V this is not seen as a logic high and will cause the CPU to lock up. If you find on the outputs any voltage around 3V then replace this PIA.
I chased and chased a fault with a logic probe and came up with nothing. tested with DMM and got 3V on one of the outputs, so then i wondered - is this enough for logic high?

Replaced PIA - got 4V or so and game booted.

Worth a check

Gav, which pin on the 6821's am i supposed to check ?

[humpalot]

Think this site will help you with your problem.

http://pinball.flippers.info/system6repairpart4.asp#noledsystem7

[Retropin]

Check pins 2 - 17, these are the outputs. Make sure you have 5V supply to the PIA first of course.

In all honesty though, if test points are OK except TP (4?) - Blanking. I would be looking there.

Blanking signal makes sure you have a good 5V supply, if not it shuts CPU down to prevent damage. All this circuit does is "test"the 5v. Problem is that if the blanking circuit fails then the good 5v cannot get through to CPU and game wont boot. By jumping the 5V to pin 37 on interconnector, all you are doing is by passing what maybe a faulty circuit. If its not faulty you can do no harm as the blanking itself is working and rendered CPU asleep. you can only overrride the Blanking IF it is faulty.

Turn game off - jump the 5v to pin 37 and turn game back on

[Pinfan]

I tried jumping 5 v into the blanking section, as per clays guides...

Did it step by step word for word...

No change...

Now everytime i power up the machine the 2, 4 amp, 5 v logic fuses blow on power up, everytime ??? 

Got bitten twice, won't get bitten a third time !

So the 5 v doesn't travel past the fuses anymore !

Not sure if its something i did or if it inevitably was going to happen.

Thanks Humpalot for your direction, I have read Mark's guides extensively, he is a little more complex then Clay.. I only know the basics when it comes to electronics i'm afraid.. #$# #$#

[Retropin]

Jumping the 5v simply takes the 5v to the CPU board as this goes from the blanking to CPU via pin 37.

There is no reason why simply doing this would cause the 5v fuse to blow.

Blowing fuses suggest a short somewhere - you may have inadvertantly shorted something. Continual blowing of fuses means the short is still there.

Take the driver board off and check that you havent a short across pins 37 - 38 or 37 - 36. its easy to do.

Check that the legs on the transistors in blanking circuit arent touching etc etc.

ill dig out my notes and also check Clays guides to refresh my memory.
Weve gone backwards here and need to get you back to a non booting CPU

[humpalot]

Pull the power supply out of the machine.  With a DMM test the +5volt DC regulator transistor and test the 2 diodes on the board.  If these test OK then the power supply is OK.

[Pinfan]

Thanks guys.

OK tested the +5volt DC regulator transistor and tested the 2 diodes on the PS board. All test fine. Tested the bridges out of curiosity, both test fine.

Checked driver board and all looks fine...Tested the transistor in the blanking section and it tested fine. Visually checked it too, all good.

Have run out of 4 amp slo blo fuses, so turning the machine on to test the PIA's will have to wait until i can find/purchase some.