(Topic ID: 238725)

Tilt Lamp for Stern Stars


By FatPanda

11 months ago



Topic Stats

  • 5 posts
  • 2 Pinsiders participating
  • Latest reply 11 months ago by FatPanda
  • Topic is favorited by 2 Pinsiders

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Linked Games

  • Stars Stern Electronics, 1978

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LDB_SCR_MCR106.jpg

#1 11 months ago

I'm having an issue with the tilt lamp not working on a Stern Stars that I'm babysitting for a buddy. Per quench:

Quoted from Quench:

Ok, maybe doing these tests in lamp test mode wasn't a good idea since it doesn't help your multi-meter to give steady readings.
Please open up a support thread for this in the "Tech: Early solid State" subforum so this thread can return to normal discussion about the games.
Try the following and answer in your new thread.
Install normal incandescents in the Tilt lamp socket and also the Ball In Play lamp sockets.
Start a game and put it in Tilt mode.
Measure the voltages on the lamp driver board at the following locations (black multi-meter lead connected to TP1 GND on the lamp driver board and leave it there).
Measure these locations for the Tilt lamp:
U4 Pin 14
U8 Pin 14
U8 Pin 15
Q47 gate leg
Measure these locations for the Ball in Play lamps:
U1 Pin 14
U6 Pin 11
U6 Pin 12
Q16 gate leg
.
Both these lamps should be lit so we're comparing voltages for their selection and drive circuits.
.
The following images are to clarify IC pin leg numbering anti-clockwise:
.
[quoted image]
[quoted image]

I'll get this info in the next day or so.

#2 11 months ago

quench
The values are as follows with incandescent bulbs installed at each location

Measure these locations for the Tilt lamp:
U4 Pin 14 21.1 mv
U8 Pin 14 21.1 mV
U8 Pin 15 22.1 mV
Q47 gate leg 22.1 mV

Measure these locations for the Ball in Play lamps:
U1 Pin 14 25.1 mV
U6 Pin 11 25.1 mV
U6 Pin 12 31.0 mV
Q16 gate leg .566 V

#3 11 months ago
Quoted from FatPanda:

So when I test the right leg on TP3, it doesnt light.

Sorry I missed this point from your last post on the Bally thread. It says the SCR is not working.
Pull the lamp driver board out of the game.

Make sure you have zero ohm continuity from:
- The cathode (left) leg of the Q47 SCR to the cathode of any other SCR (all cathodes are connected together to ground).
- The anode (middle) leg of the Q47 SCR to pin 10 of J2 (remember connector pin numbers start from the bottom and count upwards on the lamp driver board)
- The gate (right) leg of the Q47 SCR to resistor R49 just next to it.

Next, test the SCR with your multi-meter (I know you've already replaced the SCR). Set the meter to diode mode.
On the back of the board, put the black meter lead on the SCRs cathode (left) leg and hold it there.
Put the red meter lead on the SCRs anode (middle) leg. You should get NO reading.
Slide the red meter lead along the anode leg until it touches the left gate leg at the same time. You should get a diode reading about 500mv to 600mv.
Now slide the red meter lead off the gate leg while it's still touching the anode leg. You should still be getting the diode reading about 500mv to 600mv because your multi-meter has switched ON the SCR using this process.

Also try it with another SCR to get a feel for the process. You should get a reading between the cathode and anode legs ONLY after sliding the red meter lead across the anode to the gate leg and then off the gate leg.

Just re-attaching the below image for reference.
LDB_SCR_MCR106.jpg

#4 11 months ago
Quoted from Quench:

- The cathode (left) leg of the Q47 SCR to the cathode of any other SCR (all cathodes are connected together to ground).

This is the only thing that does not check out. All of the other SCRs are connected to each other and to TP1. This is not connected to anything.

I should replace the SCR with another and hope it works, or is there another way to ground this leg an confirm that it works first?

#5 11 months ago

There was corrosion preventing the cathode leg from being grounded. I removed the SCR, cleaned the area with vinegar and iso alcohol, soldered on a new SCR and now it works.

Thank you!!!

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