[GreenKeys] Model 33 Q1 transistor replacement

[Chuck Rehor]

Paul, are you sure it isn’t the big resistor? It sure looks toasty.

On Mon, Jul 21, 2025 at 12:16 PM Paul Newland, ad7i <ad7i at ad7i.net> wrote:

> It's probably not all that difficult to find a working replacement, but in
> a different form factor.   Can you show a larger portion of the schematic?
> I'd like to see if this transistor is operating as an on/off switch, or if
> it's trying to work some magic to regulate the voltage on the magnet for
> fast pull in and then low current idle.
>
> Some basic DC measurements might give you some insight into the health of
> the transistor without removing it from the circuit board.
> I'd be curious to know the voltage from base to emitter when the
> transistor is "ON" (or supposed to be on).   Also (can't see that part of
> the schematic) but if there's a resistor in series with the base I'd be
> curious to know the voltage across the resistor (and the resistance of the
> resistor), and then use ohms law to determine the base current.  Same thing
> for the selector magnet current, if that's possible.
>
> Paul, ad7i
>
>
> On Mon, Jul 21, 2025 at 10:22 AM Erik Bruchez <erik at bruchez.org> wrote:
>
>> Hi all,
>>
>> I am trying to troubleshoot a Model 33 selector magnet circuit. I don't
>> know for sure yet but there is a chance that it's the Q1 transistor on the
>> board. I am wondering if anybody here has ever replaced this transistor,
>> and if so with what (possibly more modern) part. The original is
>> Motorola-branded and labeled 181671. The schematics call it a "high gain"
>> transistor.
>>
>> -Erik
>>
>> [image: C6BC2216-1423-4DCB-A6BF-7869D424140C.JPG]
>>
>> ______________________________________________________________
>> GreenKeys mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/greenkeys
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:GreenKeys at mailman.qth.net
>>
>> >>> Jordan Spencer Cunningham's GreenKeys Search Tool:
>> https://teletype.net/gksearch
>> >>> 2002-to-present greenkeys archive:
>> http://mailman.qth.net/pipermail/greenkeys/
>> >>> 1998-to-2001 greenkeys archive:
>> http://mailman.qth.net/archive/greenkeys/greenkeys.html
>> >>> Randy Guttery's 2001-to-2009 GreenKeys Search Tool:
>> http://comcents.com/tty/greenkeyssearch.html
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>> Message delivered to ad7i at ad7i.net
>
> ______________________________________________________________
> GreenKeys mailing list
> Home: http://mailman.qth.net/mailman/listinfo/greenkeys
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:GreenKeys at mailman.qth.net
>
> >>> Jordan Spencer Cunningham's GreenKeys Search Tool:
> https://teletype.net/gksearch
> >>> 2002-to-present greenkeys archive:
> http://mailman.qth.net/pipermail/greenkeys/
> >>> 1998-to-2001 greenkeys archive:
> http://mailman.qth.net/archive/greenkeys/greenkeys.html
> >>> Randy Guttery's 2001-to-2009 GreenKeys Search Tool:
> http://comcents.com/tty/greenkeyssearch.html
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to chuck at rehor.com
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.qth.net/pipermail/greenkeys/attachments/20250721/0fb37d63/attachment-0001.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: C6BC2216-1423-4DCB-A6BF-7869D424140C.JPG
Type: image/jpeg
Size: 5479429 bytes
Desc: not available
URL: <http://mailman.qth.net/pipermail/greenkeys/attachments/20250721/0fb37d63/attachment-0001.jpe>