[GreenKeys] What an Idiot!

Tue May 28 13:03:50 EDT 2013

I was curious about the transistor too so I've looked at a few prints
and parts lists and they sure keep the details of that puppy a secret.

I think the "7339" you've found marked on it is indeed a date code as
others have pointed out.

The Teletype part number is 181675 which was sometimes marked on the device
(house numbering).

Some indications are that it was a Motorola device...  MJE family.

It is pretty much a general purpose PNP switch with no spectacular
requirements I don't think.  Appears to see about 20v across it from
-20V supply to ground with the selector magnet as the load.

I've attached one page of M33 schematic set where the two transistors
and power supply in the unit are shown.

I would be tempted to try a modern, readily available device such as
MJ2955 and see how that works in the event your device is truely smoked.
The package and pinout appear to be the same so should be an easy swap.

For reference,

http://www.digikey.com/product-detail/en/MJ2955/497-6712-ND/1038920

I'd also check the -20 and -4.7V supplies to make sure those are still
correct.  If you had 2X the input voltage at T1, the zener ZD1 was
potentially also at risk.

Chris N0JCF

On Monday (05/27/2013 at 12:32PM -0400), Teletypeparts wrote:
> 
> Rob,
> 
> I have never delved deep into the SMD card or the 500 MA transistor that sits behind it.  Probably because I never needed to so I cant be of much help there.  
> 
> I do have some power (500 MA) transistors that are new or good and a couple of SMD cards on hand if you think you need them.  
> 
> Look some more to make sure the kybd break key is not causing the trouble or any other obvious issue.  
> 
> I dug out the books and checked more for you.  
> 
> I measured the input (pins 1 and 2) to the large power tranformer and it is not open, its about 8 ohms, the book says 29 ohms, but I suspect what I got is correct as I checked it on a spare transformer and on the transformer in my spare UCC-6.  
> 
> I think you have a burned out primary in your transformer.  I am attaching 4 pics.  The first two are FS-1 receive.  The second two are the SMD card print.  Print them and cut off the edges on the second sheets and you can carefully line them up and tape them together.  Real cut and paste.  
> 
> Sorry I couldnt fit them into the scanner any better but I think they will help you.  
> 
> Wayne
> 
> 
> 
> -----Original Message-----
> From: Robert Jarratt <robert.jarratt at ntlworld.com>
> To: 'Teletypeparts' <teletypeparts at aol.com>; info <info at drukknop.nl>; greenkeys <greenkeys at mailman.qth.net>
> Sent: Mon, May 27, 2013 7:30 am
> Subject: RE: [GreenKeys] What an Idiot!
> 
> 
> 
> I checked the transformer underneath the fuses. The resistance across the wires going into the primary and the secondary sides appears to be infinite, which I believe is a good thing. The resistance across the two input wires and the across the two output wires is zero. All these things would seem to be good to me.
>  
> I assume the power transistor is the one under a plastic cover mounted on a large L-shaped piece of metal behind the SMD PCB marked 181675. I am not sure of the pinout of this transistor, but, after removing it from the circuit, I used my diode tester to measure across the terminals in all combinations and directions, I got readings of 0.14V, infinite, 0.91V, infinite, 0.15V, infinite. I suspect this transistor is damaged. What is the spec for it?
>  
> There appear to be two transistors on the SMD card. My desoldering skills are very poor so I would rather not desolder them for testing at this point unless I have to.
>  
> I am not sure which coil is being referred to, so I have not tested that, unless it the transformer. I cannot see any burned wires.
>  
> Regards
>  
> Rob
>  
> 
> 
> From: greenkeys-bounces at mailman.qth.net [mailto:greenkeys-bounces at mailman.qth.net] On Behalf Of Teletypeparts
> Sent: 26 May 2013 18:45
> To: info at drukknop.nl; greenkeys at mailman.qth.net
> Subject: Re: [GreenKeys] What an Idiot!
> 
>  
> 
> Rob,
> 
>  
> 
> Check the 3 fuses in the UCC-6 first.  They are on top of the UCC-6 toward the back.  Hopefully one is blown.  
> 
>  
> 
> After that, could be anything.  The SMD card, the power transistor mentioned by Simon, the large transformer under the fuses, burned wires.  
> 
>  
> 
> Look for the easy fix before you dig too deep.  
> 
>  
> 
> How did you manage to plug a 120 VAC style end into the 220 UK?  I thought they were very different in style.  
> 
>  
> 
> Wayne
> 
> 
> 
> 
>  
> 
> -----Original Message-----
> From: Simon Claessen <info at drukknop.nl>
> To: greenkeys <greenkeys at mailman.qth.net>
> Sent: Sun, May 26, 2013 1:26 pm
> Subject: Re: [GreenKeys] What an Idiot!
> 
> probably the switching transistor. the thing on the big cooling metal. 
> also the connected pcb might contain some blown transistors as well. 
> fortunate the documentation is readily downloadable but extensive. You 
> may want to look at doc 574-100-103TC page 20 for a schematic. also 
> check the power supplies and measure the coil resistance. if it is 
> infinite, the coil sould be replaced as well as the transistors.
>  
> good luck!
>  
> On 25-05-13 20:50, Robert Jarratt wrote:
> > I mistakenly plugged my ASR33 directly into the UK mains (240V/50Hz)
> > rather than via the 110V transformer. It blew two fuses in the plug
> > before I realised what I had done wrong.
> > 
> > The machine now runs open (i.e. “chatters”) even in LOCAL mode.
> > 
> > What might I have damaged?
> > 
> > Regards
> > 
> > Rob
> > 
> > 
> > 
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>  
> -- 
> Met vriendelijke Groet,
>  
> Simon Claessen
> drukknop.nl
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> 

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-- 
Chris Elmquist

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