LPC arcing in mech relay contacts.

i have only noticed this for the first time today, since re-installing the mech on my LPC-1 ... that i see arcing and a wee bit o' smoke when the record rejects, and when the carriage changes direction during the scan. it's coming from the front of the mech, to the right of the tonearm, what appear to be relay contacts.

i got a brush and swiped the contacts a few times. now it no longer happens on the reject, but i still see it on the carriage direction change. no more smoke, but it still arcs. i don't recall ever seeing this before, but i've only had the LPC for a couple of months.

whadday'all think??

cheers,
eric

Eric, this indicates either poor contact condition and/or inadequate wiping action.

Pitted contacts reduce the effective area of contact thus overloading the remaining point of contact.

Wiping is necessary to both self-clean (to an extent) and assure adequate point pressure.

BTW: The place where this sort of arching often occurs is in the points in the vertical stack that add the section of the run capacitor in scan/handling mode.

If you haven't already read this, it should help here:
viewtopic.php?f=3&t=6404

Rob-NYC

Eric,
On the Reversing Relay, and the one in the Autospeed, as used in the Seeburgs, I find that unless "adjusted" by one of Rob's Geppetto friends--these are VERY reliable relays--except for one common failure--the bearing surface that holds the relay blades steady, tends to loosen itself from the armature. At this point, the "Gepetto" does not see/realize this, and begins "adjusting". What you need to do is examine this situation, and if it is, in fact the problem, fix it, prior to adjusting anything !! I fix it with either "Airplane cement" or an epoxy. The armature and bearing plate must be held so they are 45 degrees from each other while the glue is drying. Allow enough time for whatever glue you use to dry. I put a bead of glue on top and on the bottom of that junction. At that point look at the contacts themselves and follow what's printed in the Service manual for adjustment and what's above-- It should operate without any "sparking", when correctly adjusted ! Ron Rich

roger, guys, and thanks. i had actually perused the "Contact points" sticky thread a while back, strictly for my own entertainment, without realizing what contact points necessarily were. i was thinking it was strictly about the tormat pins or some such. funny how you probably wont grok something until you have to fix it. so i scavanged a business card (some really old business!) and contact cleaner and went to town on the relays. it took a few rounds, but i just now made a few passes of the mech with no sparks. i'm gonna let things dry and call it a night.

i'm wondering if i got some oil on the contacts the other day which may have aggravated the situation. they were dirty enough, judging by the card stock, but especially after some subsequent 'dry rubs' did it seem to behave.

'Contact wipe' is a remarkable new concept to me! i get the theory now, but i can't say that i can tell if it's wiping well. but it definitely was a little dirty. hopefully that's it!

Didja check the contact points for "pits/burrs"-- they should smooth as a "baby's bottom " !
"Dry"-- I sure hope you did not use anything that "leaves anything" on them--??
Ron Rich

hi Ron! i really can't see the contact points on the suspect blade. it's one of the most concealed contacts, behind and underneath the other, well-functioning ones.

i just got the mech back in (always a minor ordeal...), so i'm not in a hurry to pull it out for a closer look! but i've got another issue that may have me pulling it for better access... all in due time...

not to worry, from what it tells me, my contact cleaner has no lubricant, residue, plastic-safe, etc. i just went a *little* heavy on the sauce, as i suspect i got some oil on the contacts while fumbling a lube earlier... several rounds with moistened card stock, then a few dry ones ... until the dark sludge subsided. with all that 'juicing', i thought i'd give it some time to breathe...

the next morning, i was greeted with a 20% arc rate... better than before, but kind of a bummer... today, it has been scanning without incident several times over.
but i'm curious to take a gander at those contacts when i get them on my bench with ye olde magnifying lense...

Hi Eric,
On the LPC-1, I set the mechanism to the "inspection area" in front, sit my arse down in front of that area. reach inside with a 1/4 inch "ignition wrench", and remove the ( one ) screw holding the relay coil bottom, into the frame--use caution that you do not force the mechanical catch-it will bend- and just remove the whole relay assembly--you will have "JUST enough" wire length to flip it around and see/service those contacts--Ron Rich

Ron Rich wrote:Hi Eric,
On the LPC-1, I set the mechanism to the "inspection area" in front, sit my arse down in front of that area. reach inside with a 1/4 inch "ignition wrench", and remove the ( one ) screw holding the relay coil bottom, into the frame--use caution that you do not force the mechanical catch-it will bend- and just remove the whole relay assembly--you will have "JUST enough" wire length to flip it around and see/service those contacts--Ron Rich

excellent - i'm becoming quite familiar with this working position... and recently re-deployed a funky low-boy chair from out of the garage to wit:





...so many symptoms ahead, might as well try to stay comfy

Cool--I sure cooda uzed that when I rebuilt over 500 of the LPC-1's for commercial use !! ( come to think of it, maybe that's why my back is so---bad now ?? )
Ron Rich

indeed i have noticed that standing and working above the mech, from the dome area, is pretty stressful on the back. i try to keep flexing and moving between tweaks. working down below has become rather enjoyable since i found that chair!

it started arcing again, as i was running the mech after a lube and second cleaning of the suspect contacts... then on the final reverse of the scan, it blew the main fuse wow... i guess that was quite a surge? what happened? too much current to ground? where does it short to? i've never really worked with relays and blade switches before. i've seen them arcing on old elevators and such, which looks scary, but seemed somewhat common.

i had figured that i didn't want to run it too much, but the cleaning had stopped it - but for only a couple of days of testing


anyway... i don't see a rating on the fuse, but the cap says Buss 6.1/4 GMQ

i just looked it up ... is this really a 12 dollar fuse? the one that was in there doesn't fit inside the cap - it's a bit too wide in diameter. wondering if it was correct, but there's no markings on it. it seems unusual enough of a fuse that i'll have to order it online i suppose

also - what size of a contact file should i be using? if y'all could point me to a detailed resource regarding filing, and especially - burnishing this size of contact... i have never considered burnishing.

oi...

Understand what is going on in that relay. If you look at the setup of the contacts and how it reverses the motor you'll see that if the center blade on both sides has not separated from one outer blade before closing with the other it throws a short across the AC line.

This will also happen with the simpler switching done on the older models and all that don't have to play A&B sides consecutively.

Examine the blades under good light and manually press down on the phenolic insulator. Note that there is a break-bofore-make occurring.

Make sure there is just a bit of upward tension of the center blade to help overcome any tendency to "linger' against the lower blade.

Is the phenolic guide attached firmly?

Sometimes I have noted too little up-down travel of the phenolic blade guide on certain relays in general. What often helps is to loosen the two screws at the rear of the relay and lift the whole contact assembly up while tightening the screws again with the contacts in the now higher position. That may buy a fraction of an inch more clearance. On the LPC there is also the hold linkage to consider.

On fuses, I replaced the redcap holders with regular ¼" holders and 4A-slo fuses. As with all older machines, I add fuses to all the sources from the main tran as well. It is ridiculous to spend a lot on what are essentially obsolete fuse types that don't really offer enough protection anyway.

Rob

Cat,
Read the above post about "contacts" !
On the GMQ fuses-- Seeburg was forced to use these by UL. These are supposedly a non-tamper-able type fuse !
HOWEVER, left/thanks(?) to Rob's Geppetto friends, there is a way to get around this--
If un-molested, one can carefully break the glass portion of a blown fuse, and VERY CAREFULLY dig the glass out of the metal enclosure.
Once that has been done a "regular size" slo-blo, type fuse, can be dropped into the socket, and the red cap secured in place--
Ron Rich

Yep, I was shown that trick by no-other than the head of service at Albert Simon here in NYC. He didn't approve of such things...of course.

There is one minor problem in doing this, the 'new" fuse does not come out with the cap and must be removed with a needle-nose pliers. In the case of the LPC's and a few other instances that are hard to get at, I just replaced the whole holder to so that I wouldn't have to dig at it.

For home use the trick Ron mentions is easiest...IF you don't mind laying on your belly and reaching in with pliers to extract the blown fuse....unplug the set too.

Here is what it looks like:

http://s1192.photobucket.com/user/Rob-N ... rt=2&o=179

Rob

Rob, and all,
You do realize that the GMQ series fuses came in various sizes and that the sockets used differed in size range as to which one could be inserted. I don't recall the exact size ranges anymore (old age--too much "stuff",up there !) but it went something like the following:
Up to 1 amp for the first size, from 1.6 to 3.2 for the next size, and up to 6.25 for the large size--SOME of these holders are marked as to size, inside on the "tin"--
Oh, and Rob-if a "regular size fuse" is inserted, you do not need "tweezers" to remove it--just press down on it and allow the spring to snap it out--I do not "approve" of this either, but have done this on a Friday night in a bar, with 5-6 drunks standing axking "whhen you goona get that dam thing fizzed " ?? --I have all sizes in stock, here in the shop---Ron Rich