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 Post subject: Triplett 630 PLK Type 2 troubleshooting
PostPosted: Feb Fri 02, 2018 9:51 pm 
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Joined: Jan Mon 29, 2018 6:56 pm
Posts: 1
Hello,

I picked up a mostly non-working 630PLK Type 2 and am looking for advice on how to approach repairing it.

If fed 30V from my PSU the 100K range kind of works on shorted leads, in that the needle moves towards the end of the scale, but it doesn't seem to stay zeroed.

The other resistance ranges seem dead, whether using a battery or providing 1.5v from a PSU.

The voltmeter works, kind of -- it's dramatically off reading around 10v when attached to a 20v source, around 15v with a 30v source.

The pictures I've seen of 630 PLK wiring don't look like mine -- for starters, part of my protection circuit isn't on a board attached to the relay, it's sealed up in a cardboard tube. The components in the rotary dial are all mostly a uniform brown and sleeved in plastic. And I don't see whatever the little silver knobby looking enclosures are visible in loots of the photos I'm turning up via google.

One of the red wires coming from that tube by the protection relay connects to a solder point behind the meter face where it meets another red wire coming from the DCV-Ohm-ACV/DC- function switch and then goes to the movement (I presume). There seems to be the remains of another wire there that was snipped off, but I don't see any missing connections elsewhere so I'm wondering if it was just detached and resoldered.

I will post some pics shortly but any advice would be appreciated if this sounds familiar.


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 Post subject: Re: Triplett 630 PLK Type 2 troubleshooting
PostPosted: Feb Sat 03, 2018 6:01 am 
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Joined: May Fri 01, 2009 3:53 am
Posts: 1473
Location: Glendale, California
The early PLK series had the protection circuit sealed in the tube. Later series had a board. Sounds to me like it's either horribly miscalibrated, or the protection module has failed (which the early ones did frequently). My PLK is sitting on my bench at work, where all my documents are as well, so I can't be of much help this weekend. Fred Scoles would be the guy to talk to on Triplett VOM's. He has more documents on them than I do, including the diagrams for the PLK modules.

_________________
Recently unemployed Analog Meter Technician. Simpson 260 specialist.

John, KK6WHY


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 Post subject: Re: Triplett 630 PLK Type 2 troubleshooting
PostPosted: Feb Sat 03, 2018 6:10 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 4329
Location: Charleston, W.Va.
Hi Charlie,
+1 to John's post above. Fred Scoles is the guy you need to talk to. Perhaps he may see this thread and reply, if not you should contact him via PM here in the forum.

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Poston


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 Post subject: Re: Triplett 630 PLK Type 2 troubleshooting
PostPosted: Feb Sat 10, 2018 12:21 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 2009
Location: Oswego, NY, USA
I can offer a few comments, and some (hopefully) relevant PLK history. The first 630-PLK (Type 1) run started Jun14,'63, some months after introduction of like-designed Simpson260-4P. PLK Type 1's were made thru PLK Run 3 Feb15,'64. Type 1 & 2 PLK manuals show the horizontal cardboard tube, used in production until early PLK Type 3 production (~late ’69?)...so your Type 2 PLK should have the original cardboard tubed "Cut-out Module" (later called "Overload Protection Module"), Triplett P/N 11673A. Unfortunately, a parts list and circuit diagram of the tubed parts was not shown in user manuals or any factory drawings or memos I have, as my set of prints is not complete; all I have on the cardboard tube version are a few memos between Triplett engineering and two early PLK field test companies, Dayton (Hobart) and Columbus (RobertShaw), that discussed 3 recurring problems with the cardboard-tubed/early protection circuit.
PLK Type 2 first Run#4 started Jul 13,'64 thru Run#11 started (?) early 1970, with no documented changes in the protection relay or its circuit from Type 1's. Three noted problems with this cardboard tubed version were:

1) It sometimes didn't hold a stable trigger threshold, it would either trigger too soon or not at all;

2) relay sometimes wouldn't reset correctly, so they redesigned the mechanical parts a few times (according to a series of engineering memos, but I think this was solved before the Type 2);

3) Certain HiV or RF interference fields would sometimes false-trigger the protection circuit relay Off.

PLK Type 3 introduced the more familiar open (no tube covering it) protection circuit board; vertically mounted board P/N 87-160 (P/N 87-416 on VOM model 990 T2 & T3, which is identical to mid-late PLK T3 except for the 990's Maintenance scale) measures about 1"H X 1 1/2"W, located just beside the relay; it contains few parts, one 3N81 (4-wires from small metal can) switching transistor, 3 resistors, 5 diodes (all are common 1N4004 types), & 2ea small 60V disc caps .01uf. If one has an otherwise good/working Type 1 or Type 2 PLK (with the cardboard tube), it may be possible to homebrew/retrofit this newer, better type protection board; I could later take a few photos of it. Later PLK Types (4,5,etc.) changed the protection board's part number, but I don't know if its design changed significantly from Type 3. I have several PLK Type 3's, but nothing newer to refer to.

PLK Type 2 circuit diagram in the user’s manual, shows five wire leads from the X3/Overload Protection Module (the cardboard tube) colors Brown, Violet, Black, Red, & Green; all five wires are connected into the tester....so I don't know what your disconnected wire might be, or its color? You will need to trace the wires while referring to the Type 2 ckt diagram. Type 3's with the protection circuit board (instead of the cardboard tube) shows essentially the same VOM circuit diagram as Type 2, and the same five wires color coding (between the protection ckt and tester ckt).
Some basic steps are missing from your troubleshooting procedure above. I don't know if you've completed them: check the meter movement's response (for both ua and mv fullscale deflection), linearity & (mechanical) balance; check all wiring for signs of corrosion and "cold" solder joints, correcting as needed; exercise (rotating full circle, several times) the rotary switch to help clean its wafer contacts as the manual instructs, then further clean any contacts if necessary (per ARF discussions, don’t spray anything near the switch/phenolic wafers, but precisely place small droplets of deoxit-d5 or equiv on each contactor); remove any corrosion from battery contacts; check mechanical spring action/resetting of the protection relay and clean/polish its main contacts (I use a good, clean U.S. dollar bill dampened with a bit of residue-free contact cleaner, pulled thru the closed contacts). It doesn't hurt to check-verify the relay’s contact Ohms-resistance, because good readings for all the ranges depends on the relay working perfectly. All your listed problems might be caused by corrosion or dirty contacts in switches or the relay, or in the panel jacks from the tester setting years w/o any use. Your older (brown, 1%) carbon film resistors can drift with age, especially the higher MegOhms values; check them also for stable Ohms readings, as sometimes older resistor wire leads aren’t well connected anymore; check the "meter protection diodes" which can fail usually from a previous over-current accident. Archived PM discussions describe these procedures and additional items that might need checking as you work through your PLK T2.

Our original poster has only one ARF posting, so if they don't refer back, this may be of use to others.

Fred


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