[GreenKeys] Problem with Selector Magnet Driver Circuit on ASR33

Mon Jan 14 16:53:02 EST 2013

I have been trying to determine if Pliobond is available in the UK but there seem to be different types, one link led me to an Aerospace company and it seems to be quite a specialist adhesive at least in the UK. What kind of glue is it?

Regards

Rob

From: greenkeys-bounces at mailman.qth.net [mailto:greenkeys-bounces at mailman.qth.net] On Behalf Of Don Robert House
Sent: 13 January 2013 23:24
To: r.jarratt at computer.org
Cc: <greenkeys at mailman.qth.net>
Subject: Re: [GreenKeys] Problem with Selector Magnet Driver Circuit on ASR33

Pliobond works good for this type of thing.  If you want to save energy unplug the machine when not in use.  This goes double for Model 35.

Don K9TTY

Sent from my iPad

On Jan 13, 2013, at 3:44 PM, "Rob Jarratt" <robert.jarratt at ntlworld.com> wrote:

Given that the trace is still intact, just raised off the board I would like to glue it as you suggest. Any suggestions as to what kind of glue to use?

Regards

Rob

PS Now that I fixed a problem with carriage and its connection to the codebars it is working in local mode, I am so so pleased!! Now I just need to get it to work in online mode, it already has an RS-232 box of tricks, so it should be pretty simple.

From: greenkeys-bounces at mailman.qth.net [mailto:greenkeys-bounces at mailman.qth.net] On Behalf Of Clay Archer
Sent: 13 January 2013 20:22
To: r.jarratt at computer.org; greenkeys at mailman.qth.net
Subject: Re: [GreenKeys] Problem with Selector Magnet Driver Circuit on ASR33

Yes, that’s normal for it to get hot.  It’s live even when switched “off”.   You can find a schematic and parts list at www.bitsavers.org/pdf/teletype .   R7 should also be getting hot.

You can secure the resistor by wrapping and soldering a piece of bare wire around the leg on the top side of the board so the resistor doesn’t push through.  Solder a piece of wire across any traces that are broken or lifted.  The idea is to make the lifted trace thicker with wire and solder.    You could glue the trace back onto the board but it’s not necessary.  I suggest you unplug the teletype when not in use, or put it on a switched plug strip.

Clay

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From: greenkeys-bounces at mailman.qth.net [mailto:greenkeys-bounces at mailman.qth.net] On Behalf Of Rob Jarratt
Sent: Sunday, January 13, 2013 7:13 AM
To: greenkeys at mailman.qth.net
Subject: [GreenKeys] Problem with Selector Magnet Driver Circuit on ASR33

I have noticed that when I plug in my ASR33 one of the parts becomes very hot, even when the ASR33 is switched off. I have located the source of the heat as a circuit board because there are tell-tale heat marks on the board and I can feel the heat there too. The heat marks correspond to the large area of solder on the back of the board, and the large resistor (R4) looks mottled and has no markings (possibly burned off?). Oddly, the large solder area does not appear to be connected to anything, I checked with a multimeter. From the markings on the metal plate that covers the board it would seem that R4 is getting very hot, the markings on the board suggest that R2, R5, R6 and R8 are also getting hot.

On the back the board is marked 181823 and on the front it is marked 181821. The former part number is not mentioned in the parts document, the latter seems to be the selector magnet driver circuit and the description seems to correspond, so I think it is right. If that is the case R4 is 0.82ohm, but I don’t know its power rating.

Also, while examining the components I moved one of them, when I did so the track on back became detached from the board, although the track is still intact.

So I have a few questions:

Should this board be live when the ASR33 is plugged in, but not switched on?

Why might there be heat marks associated with the large soldered area on the back, when it is not connected to anything?

What are the power ratings of the large resistors R2, R4, R5, R6 and R8?

What might cause R4 and possibly also R2, R5, R6 and R8 to get hot?

What can I do to reattach the detached track to the board?

Regards

Rob

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