(Topic ID: 166366)

Super bright broken lamp column


By dri

4 years ago



Topic Stats

  • 8 posts
  • 4 Pinsiders participating
  • Latest reply 4 years ago by terryb
  • Topic is favorited by 2 Pinsiders

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#1 4 years ago

I have a Hyperball driver board that has a super bright lamp column that bakes the entire circuit, if any light in the column lights up, the entire column lights up, both the 8x8 and 8x4. So far, this is what I've done:

* Replaced the TIP42 in both columns, these are TIP42G from RS
* Replaced the 2N6548 with a CEN-U45 as the 2N6548 is an obsolete component
* Verified the resistors out of circuit
* Diode tested the 7408 and the PIA
* Disconnected the playfield, the circuit still bakes
* Buzzed all solder joints and their destinations
* My index finger have a 2nd degree burn from touching the resistors

What are the next steps here? I'm thinking getting new components for the entire circuit up to and including the 7408.

#2 4 years ago

You need a logic probe now.

It goes uP -> PIA - > 7408 -> 2n6548 -> TIP42

Check the pia output. Then check 7408 output. Should be rapid pulses. You are going to find it stuck high or floating, probably at the 7408 output.

PS CEN-U45 is probably more obsolete than 2n6548. You can also us a TIP-102 transistor here to replace the 2n6584. If you change the tip-42 to a MOSFET like FQP17P06, you can use a weenier NPN pre drive transistor .

#3 4 years ago
Quoted from barakandl:

You need a logic probe now.

Thank you for your advice, I don't have a logic probe, will this one do?: http://www.frys.com/product/6508023

#4 4 years ago

Yes.

#6 4 years ago

Got the probe! Pin 3 of the 7408 is dead (no pulse or pitch), this is the exit of the gate controlling my faulty column, traces from pin 3 are good. The PIA has low pulse on both the faulty and a working column. Is this expected? Thanks!

#7 4 years ago
Quoted from dri:

Got the probe! Pin 3 of the 7408 is dead (no pulse or pitch), this is the exit of the gate controlling my faulty column, traces from pin 3 are good. The PIA has low pulse on both the faulty and a working column. Is this expected? Thanks!

If the 7408 output is floating(high impedance) the column will stick on really bright. That 7408 chip is dead, replace it. Use 74F08 if you dont have 7408.

As you have found, diode testing TTL chips looking for a voltage drop on gates is not always accurate.

#8 4 years ago
Quoted from dri:

The PIA has low pulse on both the faulty and a working column. Is this expected?

Yes. High signal with low pulses.

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