IBM transistor replacements

Alaric Nicoll alaricnicoll at
Sat Nov 27 14:40:49 CST 2021

Apologies for the previous email and it’s disgusting formatting, here is a second attempt, hopefully it’s readable. 

Thank you all for your responses and leads, 

Responses to some of your questions and some more questions: 

"Have you checked/measured whether they're actually faulty?" 

Yes I have, in the picture I have provided on the bottom there are the ends of 3 transistor leads. This was one that fell off as I removed the card and by far the worst corroded, so despite the fact that the rest still work. I need to replace this one. 

“I would suspect that these transistors are pre-drivers for the power transistors and may not be super critical to get an exact replacement." 

Would an NPN or PNP with the same HFE suffice, or do I need to know more? Forgive me but I am a complete idiot when it comes to this kind of circuit design and their tolerances. 

"Did you get manuals with the printer?  If so it should have ALDs (schematics)."

Unfortunately not, and nor can I find any online. 

"The 3286 printers and 3277 terminals where infamous for intermittent problems"

Excellent, glad I bought something that will provide the true IBM experience. 

Thank you, 


> On 27 Nov 2021, at 20:35, Bill Gunshannon via cctalk <cctalk at> wrote:
> On 11/27/21 3:17 PM, Van Snyder via cctalk wrote:
>>> On Fri, 2021-11-26 at 22:33 -0800, Brent Hilpert via cctalk wrote:
>>>> On 2021-Nov-26, at 1:52 PM, Al via cctalk wrote:
>>>> 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:
>>> Have you checked/measured whether they're actually faulty? Yes, they
>>> look terrible, but that doesn't mean they're faulty. It looks like
>>> minor corrosion of the steel case under its plating; unless it's all
>>> the way through the die is probably fine and cozy inside. The
>>> electrically active parts of the transistor typically aren't as
>>> susceptible to corrosion as the steel case is.
>>> (Notable exception to this being 70's-era TI ICs with plated steel
>>> pins. I've also seen some Motorola ICs with corroded pins).
>> The Computer History Museum in Sunnyvale, CA has two IBM 1401's that
>> are in operating order. One of the problems they had in getting one of
>> them to work was that some of the IBM transistors also have plated
>> steel leads that had rusted through. Ask Rob Garner <robgarn at>,
>> the leader of the 1401 restoration project, if he recognizes the
>> numbers.
> Make sure you keep the room air conditioning in working order if
> you want an operating 1401.  :-)
> bill

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