IBM transistor replacements

Paul Berger phb.hfx at
Fri Nov 26 23:06:16 CST 2021

On 2021-11-26 9:11 p.m., Jon Elson via cctalk wrote:
> On 11/26/21 3:52 PM, Al via cctalk wrote:
>> Dear all,
>> A while ago I received an IBM 3286 printer, annoyingly some of the 
>> transistors in the printer section have been corroded. What I am 
>> having trouble with is reading the part codes and finding a modern 
>> equivalent of them.
>> There are two types.
>> One has a Ti logo and two sets of numbers (attached). Does anybody 
>> know which numbers are the part numbers and if they are IBM house 
>> numbered?
>> Photos of the Ti transistors and card assembly: 
>> The other is an IBM transistor with what appears to be a 3 digit part 
>> code; for which I have been pointed to a list of house numbering and 
>> equivalents on the 1401 website. I was told the list is much older 
>> and I fear it might be out of date. However there is an entry for the 
>> part codes on my IBM transistors.
>> Should I trust the list for replacements?
> The cards appear to be SLT-style fabrication, it seems there may even 
> be SLT modules on one of them (the 1/2" square aluminum-capped blocks.)
> The 1401 list would be for SMS cards, they were yellow paper-phenolic 
> cards with TO-5 and TO-18 discrete Germanium transistors.  The SLT 
> vintage were generally all Silicon transistors.
> Almost all this stuff had IBM house numbers.
> Jon
The 3286 printer was part of the first generation 3270 system with 3271 
&  3272 controllers and 3277 display stations, so this is early 1970s 
technology the packaging is similar to SLT but the chip technology was 
not like the hybrid SLT modules as used in 360 systems.  I would agree 
that the parts would be all house numbered.  My guess is that the 139 is 
the type number and the other number is a date code it seems to me that 
this board is the drivers for the stepper motor that moves the carriage, 
but it has been nearly 40 years since I worked on one of these 
printers.  I would suspect that these transistors are pre-drivers for 
the power transistors and may not be super critical to get an exact 
replacement.  Did you get manuals with the printer?  If so it should 
have ALDs (schematics).

One thing I remember about the 3284 (similar but slower)  and 3286 is 
print timing was derived from two emitter wheels on the extreme left and 
if you got them to far out of adjustment, the carriage would take off 
and slam into the right frame and then come back and slam into the left 
frame making enough noise to get the attention of the customer.  These 
printers where replaced by the 3287 which was much easier to maintain, 
and while it was designed for the "New Display system" they where 
available with a interface card that would allow them to work with 3271 
and 3272 controllers.

The 3286 printers and 3277 terminals where infamous for intermittent 
problems that you would try to isolate by swapping some of the cards 
with another terminal or printer and leave a note in both explaining 
what cards where swapped and why.  It was not uncommon to old notes half 
buried in dust in the bottom of 3277 terminals that went back years.


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