Taxi--stuck coil

Shavenyak

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I'm back again w/ a problem w/ my Taxi. :)


The bell comes on as soon as I flip the power switch and rings continuously. I replaced the bad transistor associated with it but I still have the same problem. Marvin's site says:

"If after replacing the driver transistors the coil/flashlamp is still stuck on, then replace the TTL 7408 or 7402 logic chip. This TTL chip can also go bad. If there is still a problem, the 6821 PIA in front of the TTL chip can also die. "

Can someone give me an idea of where to find these two chips? Maybe I'm blind tonight. Thanks guys!
 
bob roberts should have all 3. If not jameco does. Look at the board itself, most likely the chip is either a 74ls02 or 74ls08, not 7402 and 7408.
 
Here's the path following everything backwards:

Bell Coil SM-26-600DC

Q15 TIP122 or TIP102 transistor

Q11 2N4401 transistor

U17 7408 IC

U10 6821 IC
 
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