My beloved Twilight Zone has just thrown me a problem I can’t solve. Several items have gone dead including “Start”. In looking at the Test Mode Functions, Switch Tests - it is saying the T3 has a “short” across Row3. Sure enough all the functions on this Row do not work. I have checked all the fuses and they are OK. I would think a “short” would blow fuses.
Any suggestions? I can’t even find “T3” in the machine? Thanks Lynn
Switches are inputs and a short doesn't damage anything; so there are no fuses. Switches are all handled entirely on the CPU.
It could be a bad U18, but you can test whether the issue is on the CPU or on the playfield. Remove connectors J206 and J208 on the CPU. Jumper J208-3 with each pin on J206 while in switch edge test. If they work, the problem is on the playfield. If not U18 is bad.
If it's on the playfield, check the white wire with orange stripe to every switch on that row. Look for a wire chaffing on metal, switch lug touching metal, etc. That's probably what you'll find.
Quoted from schudel5:It could be a bad U18, but you can test whether the issue is on the CPU or on the playfield. Remove connectors J206 and J208 on the CPU. Jumper J208-3 with each pin on J206 while in switch edge test. If they work, the problem is on the playfield. If not U18 is bad.
Don't forget to disconnect J212 
I would hate to replace U18 and find out later I have a ground short on a cabinet switch 
pasted_image (resized).pngpasted_image (resized).png
Quoted from schudel5:It could be a bad U18
It also could be because of battery corrosion. Please post a really good picture of your MPU board.
Quoted from lynnpin:I just replaced the three batteries and they were not in any way corroded.
[quoted image]
It is below the battery pack where most of the corrosion happens, which is where the switch matrix is on the board.
Good Morning, One question Schudel5, you stated above, "Remove connectors J206 and J208 on the CPU". By the looks of mine, (please see attached pic) I have no connector going to J206 and nothing hanging loose that should plug-in there. Do I take it that I unplug the connector on J208 and then do the test you suggest to the open "points" of the exposed J206? Please excuse my bewilderment and thanks again. Lynn
Pic of TZ J206 and J208 on board (resized).jpgQuoted from lynnpin:Good Morning, One question Schudel5, you stated above, "Remove connectors J206 and J208 on the CPU". By the looks of mine, (please see attached pic) I have no connector going to J206 and nothing hanging loose that should plug-in there. Do I take it that I unplug the connector on J208 and then do the test you suggest to the open "points" of the exposed J206? Please excuse my bewilderment and thanks again. Lynn
[quoted image]
J206 and J207 are the same. The connector with the green wires are plugged into J207 in your case, but can be plugged into J206. I'd just unplug all those connectors at the bottom of the CPU before you run the tests.
Good Afternoon, well the tests results look bad. I did as suggested and here are the results. The Switch Edge Lights showing the shorts across Row3 stayed “on” at all times when J208-3 was jumpered to any of the J207 leads. Both plugs on J208 and J207 were left in the connectors as the Switch Edge Test went dead when they were unplugged. I also did the same test with the Cabinet Connector unplugged and with the same results. If this means as Schudel5 stated that U11 is bad can it be replaced or must I purchase a new board? If I can replace it, where may I buy one and are special tools (solder suckers, heat sinks, special soldering irons, etc) and special skills needed? If a new CPU board is needed, any suggestions as to where may I purchase one?
A Second Thought - Is this failure a common one? I must say that the machine has operated excellently until now and I find it puzzling that a CPU component would fail like this; I would think that a simple short would be more likely to occur. One thing - In the Error Messages that come up when the machine is turned on and the Error Report ran, it has always shown "GND Short Row 3 WHT-ORN R3" and then listed each of the failed circuits on Row 3 of the T3 ending with "Clock Broken". After unplugging and replugging the CPU board, although the Switch Edge display still looks the same, the Error Messages are changed. First there is the same "GND Short Row 3 WHT-ORN R3" but then only "Clock Broken" The other messages do no appear. I am preparing to remove the clock connections in a hopeful attempt to find the SHORT being in the clock circuit. Any thoughts? Thanks again, Lynn
The chip at u20 is the uln2803? I think.
This is a buffer chip for the switch matrix, and often fails if someone shorts a lamp or flasher to a switch line.
I would think you will be up and going again if you replace that chip, unfortunately, it is not socketed on your board. I would install a socket.
Quoted from DNO:The chip at u20 is the uln2803? I think.
This is a buffer chip for the switch matrix, and often fails if someone shorts a lamp or flasher to a switch line.
I would think you will be up and going again if you replace that chip, unfortunately, it is not socketed on your board. I would install a socket.
U20 is the column driver, you typically don't see a ground switch fault with its failure; however this can happen if one of the column pulses out of U20 is sending a constant low level AND you have a closed switch in that column which would constantly drive the associated row low resulting in a ground short on the row with the closed switch.
The problem with the solution DNO is providing is that with no connector on J206, 207, 208, 209, and 212; it's just not possible for U20 to have ANY influence on the switch matrix, and impossible for it to cause a ground short.
Quoted from lynnpin:Good Afternoon, well the tests results look bad. I did as suggested and here are the results. The Switch Edge Lights showing the shorts across Row3 stayed “on” at all times when J208-3 was jumpered to any of the J207 leads. Both plugs on J208 and J207 were left in the connectors as the Switch Edge Test went dead when they were unplugged.
In order to test this properly, you must have no connectors plugged into J206, 207, 208, 209, and 212 at the time of testing; in order to fully isolate the switch matrix from external signals ALL of these connectors have to be removed.
Can you confirm that you tested the matrix with a fully isolated switch matrix?
Quoted from lynnpin:A Second Thought - Is this failure a common one? I must say that the machine has operated excellently until now and I find it puzzling that a CPU component would fail like this;
Its common for a playfield switch diode, broken wire, etc... to cause a ground short; however, the actually IC's on the WPC CPU board should continue to operate longer than any of us will be around. That being said, an external source such as a broken lamp or coil wire coming in contact with the switch matrix can take these parts out in the blink of an eye; because of this, its absolutely essential that you examine every wire and switch in this row to ensure they are not in contact with something they shouldn't be.
The absolute last thing you want to do is send out a board to have repaired, then install it and end up with exact same problem.
STORY TIME:
I once saw a master technician replace an obvious failed board with TWO spares, neither of which made any impact on the failure; awhile later, he found and repaired a repaired a broken wire but was still unable to get the system working despite having two spare boards! The problem here was the likelihood of having three boards with the exact same failure is so infinitesimally small that is was immediately ruled out as a possibility. What he failed to recognize is that he blew the same gate on the same IC on both spare boards the instant he installed them, as the broken wire was sending high voltage into one of the output signals of a TTL IC on these boards.
The moral of the story ... Don't be that guy.
Hi Pin Guy, thank you for taking the time to respond so throughly. As to your msg "In order to test this properly, you must have no connectors plugged into J206, 207, 208, 209, and 212 at the time of testing; in order to fully isolate the switch matrix from external signals ALL of these connectors have to be removed. Can you confirm that you tested the matrix with a fully isolated switch matrix?"
As I stated, when I disconnected all the connectors from the board, the "Test" screen on the machine’s dot matrix no longer displayed the Switch Display so that any test probing between J207 and J208 did not show a response on the dot matrix that I could evaluate as had been suggested to me (above). So I re-pluged everything back in and ran the test probes from J208-3 to each of the 9 contacts on J207, and having no effect on the now shown “Test Display”, I did it again with the Cabinet Connector J212 unplugged. Again no response.
As to your “Don’t be that guy” comment, I couldn’t agree more. My long-ago training in aircraft electronics always taught us to look for the simplest and most obvious causes to the problem, such as broken or in this case abraded and shorted wires. Thanks, Lynn
One more thing, will a momentary short of a switch wire “blow” the U18 IC so that it will no longer work even if the short no longer exists?
Quoted from lynnpin:One more thing, will a momentary short of a switch wire “blow” the U18 IC so that it will no longer work even if the short no longer exists?
All any IC chip needs to fail is any momentary short to a higher voltage. IE U20 shorted to 50 volts for even a second can destroy that chip.
Quoted from lynnpin:One more thing, will a momentary short of a switch wire “blow” the U18 IC so that it will no longer work even if the short no longer exists?
Normally when you think of a short, you think of a signal to ground condition, the grounding of any switch martix wires will not damage anything; however, shorting a coil or flasher voltage to the row or column wiring in the switch matrix, even briefly, will likely result in damage.
Thanks for the education - I do appreciate it. PIN-GUY, you keep making reference to U20. Other posters said that U20 can't be the problem for the reasons given. Do you agree the most likely IC is U18?
Quoted from lynnpin:Do you agree the most likely IC is U18?
It could be but I personally never replace anything I haven't checked. My main concern here is this statement...
Quoted from lynnpin:As I stated, when I disconnected all the connectors from the board, the "Test" screen on the machine’s dot matrix no longer displayed the Switch Display so that any test probing between J207 and J208 did not show a response on the dot matrix that I could evaluate as had been suggested to me (above). So I re-pluged everything back in and ran the test probes from J208-3 to each of the 9 contacts on J207, and having no effect on the now shown “Test Display”, I did it again with the Cabinet Connector J212 unplugged. Again no response.
What you are stating here is not normal...What I would like you to do...if you haven't already, is to power off the machine remove all of the connectors on the bottom edge of the board EXCEPT for J205 "Direct Input Switches" as your diagnostic switches are on this connector. When you power on the machine in this condition you should get a message stating something about potential blown fuses F114 or F115, just ignore these as the CPU interprets these disconnected switches as a loss of your regulated +12V that powers the switch matrix. When you go into switch test from here, all switches should read open, as it takes a low going signal (column drive from U20) to pull down the normally high inputs at the LM339s. Shorting any of the column pins to the row pins should result in a closed switch. If nothing at is working, I would pull the MPU board, place it on your workbench and firmly press in on the center of your ASIC to ensure its well seated in the socket and then put it back in the machine and test again...you would be surprised at how many odd issues this simple action can correct. While its out, go ahead and do the same for the CPU, ROM, and RAM chips.
U18-7 Switch Row3 (normally high)
pasted_image (resized).png
I guess one thing I'm still unclear on is with J207, J208, and J212 removed, did the Ground short on Row 3 remain or clear?
Quoted from Pin_Guy:U20 is the column driver, you typically don't see a ground switch fault with its failure; however this can happen if one of the column pulses out of U20 is sending a constant low level AND you have a closed switch in that column which would constantly drive the associated row low resulting in a ground short on the row with the closed switch.
The problem with the solution DNO is providing is that with no connector on J206, 207, 208, 209, and 212; it's just not possible for U20 to have ANY influence on the switch matrix, and impossible for it to cause a ground short.
In order to attempt to clear up confusion with this information I did some testing, I went ahead and took a red mini-grabber jumper and connected my column 2 pulse right to ground; I chose column 2 as column contains the always closed switch #24 (this switch is just a blocking diode on the coin door interface board) and grounding this would permanently drive row 4 low and should result in a Ground short on column 4.
What this did was simulate a U20 failure causing a constant low output on the column driver, and I was rewarded with the suspected ground fault at Row 4 that DNO was referring to.
Now if I remove J207, the ground short will go away as the failed column pulse cant leave the board; however if I remove J209, I've disconnected the playfield, but I still have a ground short since the column 2 pulse is also going out J212 and the constant low on row 4 is still there because it comes in on J212 from switch 24.
The takeaway from this is with all 5 matrix connectors removed, if the ground short remains then its not U20 and its not switch related, if it goes away then its likely not a U18 problem.
With these cables removed, the entire Switch Test matrix that previously showed Row 3 completely shorted "cleared" and the Switch Matrix was completely cleared with no "shorts" also. Previously only J208 had a connector installed; J207 was unconnected.
I apologize for my ignorance of the machine and inability to cogently explain my findings. When I removed all Four (not Five as you state) matrix connectors, the Switch Test Screen would not show on the dot matrix display, so I had no results one way or the other. As to your findings shown above, again I apologise, but they are over my head.
Quoted from lynnpin:With these cables removed, the entire Switch Test matrix that previously showed Row 3 completely shorted "cleared" and the Switch Matrix was completely cleared with no "shorts" also
Ok so U18 is probably fine.
So now you need to isolate the board (U20) from the playfield, so keep these cables removed.
Since you know the problem is on row 3, you will want to jumper your row 3 input at J208-3, to each of the column drives J206. If any of them cause a ground short, then U20 probably is bad, if they all close a single switch in row 3, then you have a ground short in either the cabinet or the playfield.
Edited...I had my row and columns reversed.
OK, in jumping Column drive J206-3 or J207-3 to each of the switch drives on J208, something took place, switches sometimes were activated and the Switch Test Matrix lit appropriately each time.
Quoted from lynnpin:I apologize for my ignorance of the machine and inability to cogently explain my findings. When I removed all Four (not Five as you state) matrix connectors, the Switch Test Screen would not show on the dot matrix display, so I had no results one way or the other. As to your findings shown above, again I apologise, but they are over my head.
I'm probably not articulating this clearly, the five martix connectors I'm referring to are the ones shown in post 5, only three of of these five switch matrix connections will have cables attached (Switch Rows, Switch Columns, and Cabinet Switches). The fourth cable located at J205 are for your direct ground switches and are not part of the switch matrix, this cable must stay connected for your coin door interface switches to function.
Quoted from lynnpin:OK, in jumping Column drive J206-3 or J207-3 to each of the switch drives on J208, something took place, switches sometimes were activated and the Switch Test Matrix lit appropriately each time.
Sorry I misinformed you, you must not have seen the edits 
Quoted from Pin_Guy:Since you know the problem is on row 3, you will want to jumper your row 3 input at J208-3, to each of the column drives J206. If any of them cause a ground short, then U20 probably is bad, if they all close a single switch in row 3, then you have a ground short in either the cabinet or the playfield.
Edited...I had my row and columns reversed.
Thank you for the clarification. In jumpering J206-3 to J208, the various J208 pins on J208 all accomplished something different. the first three threw Switches, the fourth lit (shorted) and a Row 4 light lit and the others lit lights on the other Rows. There was no duplication of a single switch in Row 4 as suggested.
The stationary wire should be on J208-3...with the other end of the jumper hitting each of the columns on J206. I think the information on pinwiki can really help you with the remainder of your fault isolation.
http://pinwiki.com/wiki/index.php?title=Williams_WPC#Switch_Matrix_Problems
Thanks again Everyone for taking the time to assist me; I am pulling the board and sending it to Chris Hibler for repair.
Just to close this issue, I thought you might like to know that I located the problem with my TW Pinball that was showing a short across the 3rd Row of the Switch Matrix. The problem (short) was in the SW10 OPTO Circuit Board, which I suppose makes sense since two of the switches on Row 3 are OPTO Switches. In isolating each switch in-turn without success, I noticed the Common White/Orange wire went to the OPTO Board through Connector J5 (-10). When this connector was disconnected the “Row 3 - White/Orange Short” and “Clock is Broken” messages were halted and the clock hands returned to the proper 12:00 starting place and the clock began working. (Obviously the machine was now showing other problems due to the OPTO Connector removal). Replacing the OPTO Board with a new one from PINBALL LIFE in Huntley, Il for $89.00 and shipping solved the problem.
Thanks again to Chris Hibler for testing and working on the WPC-089 MPU Board. I would certainly recommend Chris for Circuit Board repairs. His email is: [email protected].
Thanks to you all for your assistance and suggestions.
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