[GreenKeys] What an Idiot!

Mon May 27 14:54:34 EDT 2013

I have more info on the power transistor. It seems to be a Motorola 7339, but I have been unable to find any datasheets for it. I have also spotted markings on the metal where it is mounted so I can report the voltages from my diode tester more accurately now. Here they are:

c-e Open

e-c 0.7V

e-b 0.14V

b-e Open

c-b 0.14V

b-c Open

Does that mean it is good or bad? Seems bad to me, but it might not be an “ordinary” one.

Regards

Rob

From: Robert Jarratt [mailto:robert.jarratt at ntlworld.com] 
Sent: 27 May 2013 12:30
To: 'Teletypeparts'; 'info at drukknop.nl'; 'greenkeys at mailman.qth.net'
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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