EMRFD Message Archive 11578
Message Date From Subject 11578 2015-09-04 02:57:20 Joe Relay Maintenance Group,
I recently acquired an IC-751 LPF assembly which I would like to press into service as part of an attempt at an 160-10M Softrock 50W transceiver.
I tried to use a VNA to look at the individual filter passband, but all I was able to see was very erratic displays.
Testing each filter for DC continuity showed all the 14 relays were mostly open circuit. Several dollar bills were shortened to make an abrasive strip, and along with a very small amount of Deoxit, the relays were restored to usable status. The resistance was .6 to .7 Ohms for all the Relay-Filter-Relay paths. Reasonable VNA plots were then generated.
What can I expect going forward running 5-50W thru this filter board?
As far as what caused this situation, W8BI makes mention of the following possibilities:
Outgassing of the plastic causing a very thin layer of contaminant to settle on the relay contacts (single pole single throw)
Operation with no or minimal current passing thru the contacts.
Since all the relays were suffering the same fault, I suspect outgassing or some other environmental containment like tobacco smoke. The board itself was clean so tobacco smoke is probably not the cause.
If the board becomes intermittent, what other remedy might be useful (The relays seem to be unobtainium)?
As I initially considered what to do, I remembered a Telco tool for burnishing relay contacts that I had years ago used on Dow-Key RF relays. I grubbed around my tool box and retrieved a Plastone burnisher, 4" long, .5" wide and .036" thick. As it turned out it was too thick for these relays.
A visit to Google brought up (among several sources):
Does the 1/4” by 4-3/4” by .015” 320-Polish grit look to be useful?
(It is not clear that the grit number is the same as that describing sandpaper / Emory cloth.)
I haven't figured out the pricing and I don't think I really need 12 of them. 8-)
Any help with this (suspected) problem would be appreciated.
PS The filter topology is not in my experience. What's it called?
11580 2015-09-04 07:25:07 n2msqrp Re: Relay Maintenance Joe,
Before you try a burnishing tool could you pass a low DC "wetting" current through the relays and toggle them so that are arcing will burn off the oxide layer?
Could anyone recommend a suitable DC current level - 1ma, 10ma?
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