Switch matrix prob

[Strangeways]

Hmm,

OK, black (earth) from switch to plug looks and buzz's out fine.

Corresponding earth pin on direct switches plug J205 buzz's out fine to earth...
U17 replaced.

No value thus far....

Just recheck your work - especially solder bridges between pins.

[MartyJ]

I've gone over it again.  No obvious solder touching other sockets...A few solder pads looked a little suss , I'm thinking this is the problem....I will look for a schematic for U16....

[MartyJ]

OK, I suspect there is a damaged solder pad (poss batt damage after resocketing) for my U16 which controls direct switches.

The schematics are available from IPDB which is good, I've had a read and this is where I fall down.  Is someone able to assist me in working out where the pins from U16 should come / go so I can jumper them to see if this fixes the problem?  I'm still learning reading schematics and this is above me (again what I don't know could fill a warehouse!)...

The schematics were available from IPDB and I downloaded a copy, but I'm fearful to upload in case of copywrite issues etc...

Any help would be greatly appreciated!

[humpalot]

noted battery acid damage, did you first sand back the corrosion before treating it with the water/vinegar?  I normally remove all components in the corrosion area, then sand and treat before replacing parts.

[Marty Machine]

From what u describer, it kinds reaks of a pin being held HI or Low due to a nearby shorting pin/track...

Try metering between adjacent pins on the chip(s) you replaced, and see if there any obvious shorts there.

MM.

[MartyJ]

noted battery acid damage, did you first sand back the corrosion before treating it with the water/vinegar?  I normally remove all components in the corrosion area, then sand and treat before replacing parts.

No I didn't do this..From looking at where it had gone, it would have been a lot of resistors.  I suspect if I had removed them the pads would have gone too.

I will mostly likely get a Rottendog replacement.  They're not super expensive but no one has them at the moment..I get the feeling I will be chasing my tail in the long term.

From what u describer, it kinds reaks of a pin being held HI or Low due to a nearby shorting pin/track...

Try metering between adjacent pins on the chip(s) you replaced, and see if there any obvious shorts there.

MM.

You might have to dumb it down a bit for me MM...I've buzzed out the suspect pins with other pins around it if this is what you mean?

[Marty Machine]

Yep, just go thru each pin on the IC, and meter onto the pin either side of it, and work your way along the whole I.C.

The short may be on the 'other' end of the resistor(s) away from the I.C end, so you might also meter between resistors too.

MM.

[MartyJ]

Yep, just go thru each pin on the IC, and meter onto the pin either side of it, and work your way along the whole I.C.

The short may be on the 'other' end of the resistor(s) away from the I.C end, so you might also meter between resistors too.

MM.

Will do.

MM if you get time, are you able to look at the schematics for U16 (LM339) and see if you can decipher what goes to what.  I've found the earth pin - easy but the others seem very confusing. 

Thanks

[Marty Machine]

No probs, this is Getaway isn't it?

You might need to scan/email me a page or 2, i can't find an easily downloadable one at the moment...

MM.

[MartyJ]

File is 2mb so I cannot upload and not sure if I can?

http://www.ipdb.org/files/1000/Williams_1992_The_Getaway_High_Speed_II_WPC_Schematics_Revised_May_17_1993_.pdf

Or PM me your email and I will forward.

I just need a hand to work out whats going on?  I'm very confused as to what should be going where        

[Marty Machine]

ok, got it.

b4 i look thru the whole pdf, which page/diagram am i looking for?

[MartyJ]

Thanks MM,

Page 2.  Its U16 I'm looking at (LM339).  U16 & U17 control the direct switches.

I found one track which was done, that I've repaired.  But its hard to work out what goes where.

IF we can work out that pins 1 to 14 are suppose to go, I can buzz each one out.  I think there is one which still is broken that I need to find.

[MartyJ]

I found some stuff on RGP & hopefully is correct.

I should be getting solid 5v on pins 4, 6, 8, 10 on LM339 at U16 & U17.

On U17 - all correct

On U16 - all 5v except pin 6.

Further states should get 12v at pin 3 on U16 & U17.

On U17 - 0.01v

On U16 - 0.01v

??

[Marty Machine]

Cool, looking at it now, pretty straight-forward operation.

Which part of the diagram dont you get, when trying to trace the tracks?

IF you buzz the output pins of the LM339 (U16 pins 1,2,13,14) which goto the 74LS240 (U15a pins 8,6,4,2 respectively)
then you've proved that much.
Each of these 4 pins ALSO connect to a 10k resistor, and the other ends of those 4 resistors will (should) be all joined together which is the 5v pullup for them.

Confirm that LM339 pin 12 = GND (ground), and that pin 3 = 5v.
http://pdf1.alldatasheet.com/datasheet-pdf/view/3064/MOTOROLA/LM339.html

Inputs (-ve) to the LM339 are pins 4,6,8,10 and should be connected to 5v.
Inputs (+ve) to the LM339 are pins 7,5,11,9 and should wire to 1K resistors, the other ends of these 4 resistors should connect to diodes D14,13,12,11 respectively, to their 'Anode' ends.
At the join where the resistor connects to the Diode, there will ALSO be a 1.2K resistor connected too.
The other end of this 2nd lot of (1.2k) resistors connect to the 12v supply.

Buzz the diodes with a diode-check function on your meter too.

Assuming everything above checks out, you may have an external wiring error? a shorted/missing diode on your switch somewhere? or possibly lost a connection AFTER the output of your U20 chip.

There's a signal on the 'Direct Switches' connector named 'Enable', buit oi'd say that is ok if all the other direct switches are working?
Otherwise, replace Transistor Q1 (2N3904) and/or confirm U5f (74LS14) also works too.

I'll leave it here for now until you've eliminated all thse, then we'll dig deeper, as there's more chips that control U5f (enable signal).

Good Luck,
MM.

[Marty Machine]

You just confirmed a problem then....

Inputs (-ve) to the LM339 are pins 4,6,8,10 and should be connected to 5v.

Good Luck,
MM.