Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

   Home   Help Search  
Pages: [1]   Go Down
  Print  
Author Topic: SGC SG-500 Sticky relays??  (Read 1598 times)
KA4KOE
Member

Posts: 187


WWW

Ignore
« on: November 26, 2012, 07:51:54 PM »

I think I have a minor issue with my SG-500 amplifier. It is currently wired for manual PTT and automatic band selection. Recently, I noticed that the receive signal strength would be down about 20 DB upon returning from transmit. If I key the PTT again, sometimes it will restore full receive. Other times I have to actually activate the band selection by speaking.

This appears to be a relay changeover issue, possibly related to band selection.

My radio does not indicate any SWR issues during transmit.

If the relay is bad or simply dirty, is it the type I can replace or clean easily without shipping the sucker back to the factory?

Tnx.

Philip Neidlinger
KA4KOE
Logged
K8AXW
Member

Posts: 3651




Ignore
« Reply #1 on: November 26, 2012, 09:44:45 PM »

Phillip:  Have you opened it up and looked at the relay(s)??  Most relays can be cleaned by simply putting a piece of paper between the contacts and pulling it through while holding the relay closed with a finger.  The same process works when the relay is in its "relaxed" state.  Sometimes a piece of paper soaked in contact cleaner works very well too.

BE SURE THE AMP IS UNPLUGGED AND THE HV HAS BLED OFF!  If you're not sure about any of this Phillip, I suggest you either get someone with more experience to clean the relays or send it back to the factory. Dirty relay contacts sounds like it is the problem.
Logged
G3RZP
Member

Posts: 4366




Ignore
« Reply #2 on: November 27, 2012, 09:43:45 AM »

As that amp runs off about 14 volts , I don't think he'll have much of problem with needing to let high voltage bleed off....
Logged
N4ATS
Member

Posts: 799




Ignore
« Reply #3 on: November 27, 2012, 11:12:44 AM »

I doubt it is a relay issue , usually never is according to all those who actually find their problem. Try it into a dummy load first before tearing into it , just unplug the dummy load and plug in the antenna after each test (key-up) to see if RX is back or not. If it is back as nomal , shield the PTT line better (is my guess and usually points to the problem if you search the threads and see the results from others)

It may be a relay problem but save time and try this first...
Logged
K8AXW
Member

Posts: 3651




Ignore
« Reply #4 on: November 27, 2012, 08:31:35 PM »

RZP:  Peter, my face is red!  I apparently had a mindfart when I made the HV comment.  It was a reaction to the question..... from someone who was reluctant to even open the case and have a look at the relays.   Embarrassed
Logged
G3RZP
Member

Posts: 4366




Ignore
« Reply #5 on: November 28, 2012, 02:41:13 AM »

The FT102 is famous for this problem, and here, it is definitely the relays. Most people seem to go to an immense amount of trouble changing the relays, when all that is needed is a few resistors, capacitors and miniature RF chokes to bleed some DC through the contacts - in that case, you can't get at the contacts, and that's often the case with small relays today.

Old fashioned telephone maintenance people from the 1950s and before knew about the oxide film building  up and causing a loss of signal when switching low level AC (AF or RF!) signals, and by arranging to bleed a milliamp or less of DC from a voltage high enough to break the oxide film - 12 volts often being enough - the problems go away. Unfortunately, it seems many of today's designers have never studied the history and how the same problems were cured simply....
Logged
Pages: [1]   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!