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Contesting Online Forums : Tips : IC-751A to LK500ZC Forums Help

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IC-751A to LK500ZC Reply
by W8JJW on June 4, 2001 Mail this to a friend!
I'm having some difficulty getting this Amp keyed by the '751. The '751 says it has relay closure on transmit on it's RLY output, the amp says it wants relay closure on it's RLY input to key-up, and the amp DOES key-up the first time, then will not un-key..the XMIT LED stays on. I've checked, the VOX delays, the QSK/VOX switch on the amp, etc etc. I replaced the relay in the '751..same same. The manual for the LK500 is barebones..any advice or hints ??
RE: IC-751A to LK500ZC Reply
by SM0JHF on June 8, 2001 Mail this to a friend!
I had both (LK500ZC and IC751A) and they worked perfectly. So you must have an internal problem inside the amplifier, the control circuits are quite complicated there. And soldering of poor quality. I know my LK500ZC is now used again with IC751A and no complaints.
RE: IC-751A to LK500ZC Reply
by kr4ja on June 29, 2001 Mail this to a friend!
I have a no-tune LK500ZA which worked fine with my IC-756 until I accidently switched the QSK knob to the on position and keyed the amp while operating in SSB. Either the high voltage or current surge damaged the the relay in the IC-756 and the amp would stay keyed because the relay in the radio was now closed, permanently! This is a problem with older amps which use higher currents in their relay circuits than the Icom radios can handle. I purchased an amp relay keying line from N8MIS ( to protect the radio (it has an Icom accessory plug on one end for the radio, and a phono plug for connecting to the amp). After I replaced the Icom relay, I installed Larry's patch cable to protect the radio from any future key line surges. You might contact Larry to see if he has a cable for your IC-751A.

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