[GreenKeys] strange printing with LPR?

[ROBERT LAAG]

I HAD AN IDEA BASED ON YOUR RESULTS...  IF YOU CONNECT THE LOOP CURRENT 
METER AGAIN TO THE SEL MAGS ON THE PRINTER, AND THEN TURN ON THE REPERF 
AND SEE WHAT HAPPENS TO THE READING...  MAYBE THE RESISTANCE OF THE 
RELAY IS HIGH AND CAUSES THE CURRENT TO BECOME LESS...  WHEN ADDING 
ANOTHER DEVICE INTO THE LOOP THE CURRENT COULD DROP A BIT BUT SHOULD NOT 
DROP BY A BUNCH...  THE LOOP CURRENT THRU THE REPERF SHOULD BE OK SINCE 
IT IT DOING ITS THING OK AND PROBABLY ISN'T IMPORTANT...  CAREFULLY...   BOB

Eugene Hertz wrote:

>At several people's suggestion, I measured the internal loop current, here's what I did... There are 4 terminals on the two lpr selector magnets. My selector magnets are connected in parallel. So I have two wires coming from the internal (LESU) loop to the two connections on one lpr selector magnet, then these two connections go over to the other two on the other selector magnet in parallel.
>
>I disconnected one of the loop wires from the lpr selector magnet and inserted my ammeter between one wire from the loop and connected the other side of the ammeter to the terminal on the selector where the wire used to be.
>
>I put my ST6 on standby and read 0.05A (50ma) going through the lpr. When I disconnected the 28ASR from the jackfield, it read 0ma.  So that seems pretty good.
>
>I have not figured out a way to insert my ammeter into the internal loop without the lpr also in the loop. Is it possible that with the lpr out of the loop that I would get something more like 60ma? And could that 10ma be the difference between working and not working for the printer?
>
>Is there anything mechanical that can be set on the printer to make it more sensitive to a (potentially) lower current?  I should mention that there is a rheostat in the LESU for the loop current, but it was maxed out when I took the reading of 50ma with the lpr in the loop.
>
>I will add, then when I got the ASK from Mr. Hart. He did suggest I remove the internal loop and just use the external loop (from the ST6). I think this was more of a way to guard against an eventual (inevitable) failure someday of the LESU.
>
>Eugene
>
>-----Original Message-----
>From: WA5CAB at cs.com [mailto:WA5CAB at cs.com]
>Sent: Friday, August 25, 2006 06:49 PM
>To: ehertz at tcaf.org, greenkeys at mailman.qth.net
>Subject: Re: [GreenKeys] strange printing with LPR?
>
>Eugene,
>
>I don't know what kind of loop supply you are running and if you said it's the one that comes with a 28ASR I still wouldn't know, having owned M28 stuff but never used it. But the first thing I'd do would be to patch a 0-100 MA meter into the loop (everyone really should have one permanently installed but few do) and check the loop current. It should be either 60 MA or 20 MA with nothing being sent, whichever way your machine is wired. Sounds like your typing unit may be more sensitive to it than the reperf.
>
>And depending upon what type loop supply you have (upstream voltage and current setting type), you may have to always adjust the loop current anything you go from one to two sets of selector magnets. Usually, with a 120 VDC supply, the change is minimal but I've heard some on here claim 40 volts is plenty (which I don't agree with but that's another story).
>
>In a message dated 8/25/2006 6:26:05 PM Central Daylight Time, ehertz at tcaf.org writes: 
>Ok, so my next problem. I have not been punching tape with my M28ASR in a few weeks since the tape jammed and I was too lazy to clear it out. So its been a while. Today I cleared the jam and was printing off ITTY very well. I decided I would try to punch some tape off the loop. In my ASR it has a local loop supply that is keyed with a relay from the external loop. Everything was working fine until I switched in the typing reperf (yes I have the reset bail manually cleared from the code bars). I should mention that the main knob is in the K mode for this.
>
>When I do this, the reperf perfs perfectly fine, however the printer which is now in series with it, starts to print junk. When I take the LPR out of the loop it returns to printing normally again. I have a switch at the operators position of the ASR to switch the lpr into the loop.
>
>Any ideas? Whats baffling is that the reperf perfs away correctly, not a missed character. I would think that if the loop was being bogged down somehow by adding in the lpr that both the printer and the lpr would be degraded. There is an adjustment for the internal loop (I have never tried to measure the internal loop voltage) but I wonder if I may need to tweak?
>
>
>Robert Downs - Houston
><http://www.wa5cab.com> (Web Store)
>MVPA 9480
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