Re: Help with Thunderclock parts ID

["Apple2Steward" <none@none.net>]

"Michael J. Mahon" <mjmahon@aol.com> wrote in message 
1695200662305771718.599602mjmahon-aol.com@news.giganews.com">news:1695200662305771718.599602mjmahon-aol.com@news.giganews.com...
> "Apple2Steward" <none@none.net> wrote:
>> To my horror, I found that my Thunderclock had developed
>> corrosion on the legs of several semiconductors, one of which 
>> had
>> corroded through.
>>
>> I'm having a trouble identifying a few components for 
>> replacement
>> and wonder if anyone who is well-versed in such things could
>> help.
>>
>> A D1 there is a diode that has lost its painted-on markings. 
>> It
>> is next to R10, a 10% tol. resistor which has (reading from 
>> the
>> other end) gray - red - black bands (82 ohms?).
>>
>> The worst transistor at Q3 is marked:
>>
>> F2N
>> 3904
>> EBC
>>
>> The other at Q4 is marked:
>>
>> ~202/
>> 2N
>> 3904
>>
>> (The "~" is actually the two National Semiconductor squiggles 
>> one
>> above the other).
>>
>> Am I correct that the two transistors are the same:  2N3904, 
>> just
>> from different manufacturers (Fairchild and National?)?
>>
>> What would be a likely replacement for the diode?  Would it be
>> necessary to ID it from another Thunderclock or could I meter 
>> it?
>>
>> Any suggestions would be appreciated!!
>
> As noted, it's an 82 ohm resistor and they are both standard 
> 2N3904's.
> Any standard diode--like a 1N914, for example--will work.  It 
> only
> conducts a few milliamps and blocks a few volts.   (It's part 
> of the
> charging circuit.)
>
> -michael  -  NadaNet 3.1:  http://home.comcast.net/~mjmahon

After ordering two new aluminum C battery holders to replace the 
corroded ones and the other parts from Digi-Key, I installed 
everything today.

Interestingly, the battery holders made by Keystone Electronics 
were held to the board by solder "through hole" pins that also 
supply the electrical connection to the traces.  "Value 
engineering" I suppose.  These are not available any longer, but 
similar ones (also by Keystone) with solder lugs for the 
connectors are.

To my pleasant surprise, I discovered that the circuit board 
already had holes placed that would line up with the holes in the 
bottom of my new battery holders.  1/4" 4-40 screws with nuts and 
washers were the exact size.

So after wiring the holders and replacing the two badly damaged 
2N3904s, I gave it a try.  It was recognized in the slot, but 
wouldn't pass the self test.

I reseated the socketed IC and retried, and still no joy.  I then 
removed and replaced the batteries, and on the next try it 
worked!  Passed the self test, and set and held the time.

I'm not sure what the initial problem was.  I hadn't used it for 
6 or 7 years.

Anyway, thanks for everyone's help!!