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(Topic ID: 235836)

Seawitch boot issue, hoping for some help


By Thrillhouse

1 year ago



Topic Stats

  • 6 posts
  • 4 Pinsiders participating
  • Latest reply 1 year ago by Thrillhouse
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#1 1 year ago

Hi all,
I'm having a boot issue with my Seawitch and I cant seem to figure it out. After the 3rd ring the MPU freezes up and makes a continuous screaching noise. After messing with it for a bit I am at a dead end to the issue. If I leave J2 on the lamp driver disconnected the game will boot completely and the displays light up correctly. From what I am seeing on the schematic is that J2 controls several of the feature lamps on the playfield. What I have tested/done so far:

Swapped all the boards in the backbox with known working ones
Repinned J2 on the lamp driver after seeing a bunch of "green goo" on the black/white wire connector
Tested several combinations of leaving different connectors unplugged on the MPU, Lamp Driver and Displays - at this point I am sure that it is the Lamp Driver J2 that is the issue

Can anyone point me where to go from here? Thanks in advance

#2 1 year ago

Well, J2 on the lamp driver board just switches playfield/backbox feature lamps. There's no voltage output on LDB J2 and no inputs on J2 either.
The lamp driver board is addressed by the 6821 PIA chip at U10 on the MPU board.
When the MPU board is testing the U10 PIA after the third MPU LED flash, it pulses all the PIA outputs and some feature lamps will quickly flicker ON as a result.
My guesstimate is that one of your lamps connected off J2 is shorted to a power source so that when the PIA is being tested and it pulses the lamp board, that power source is being shorted to ground via the lamp board SCRs and disrupting system power causing your lockup symptoms.

Anyway I'd start by looking at those playfield and backbox lamp sockets hanging off the lamp boards J2.

#3 1 year ago

Those flashes are telling you where to start. Each one is a test of something else on the board.

http://www.oocities.org/timessquare/arcade/7800/flash.html

So in your case, it sounds like the PIA in U10 could be bad. That would be a good place to start.

1 week later
#4 1 year ago

After monkeying with the issue again this weekend I'm still no closer to a solution. In fact the problem is now worse. After lifting the playfield I now need to leave both J1 & J2 on the lamp board disconnected before I can get the game to fully boot.

A few things I tried before posting:
I disconnected both connectors to the back box lights and also the coin door and the problem persisted so I can rule out the back box lights and coindoor.
Measured for voltage on the ground strap and read as 0 so no issue there.
Looked over every inch of the playfield underside several times. No loose/broken wires and nothing touching were it shouldn't as far as I can tell.
Verified that all connectors are in the plugged into the correct position.

Before I start disassembling the wire harness to look for a short does anyone have any other suggestions on what to try or look for? Thanks in advance

#5 1 year ago

When I have had to chase a lamp short on a classic Stern, I usually find the problem close to a corner lamp or one along the playfield edge. Something could be pinched or crushed in that area. Also, look close under the drop target carriages as some of those carriages are very close to some lamp sockets. After that, it becomes a test of each individual lamp/socket and the wires feeding them.

2 weeks later
#6 1 year ago

I wanted to follow up on this and post in hopes of saving someone else alot of time and heartache down the line. After tearing every inch of the harness apart in an attempt to find a short I was no closer to a solution. It turned out that j3 pin25 on the SDB was not making proper contact due to the green goo from one of the wires deteriorating. REALLY wish I had looked at those connectors much closer before tearing everything apart.

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