how rare are replacements? got this guy selling new omron 3pdt relays on ebay and I'm wondering if I should pick up a few "just in case" parts.
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upd858 relay
- Thread starter space cowboy
- Start date
Humor me for a minute. A uPD858 is a PLL chip. Why are relays needed for it? To switch the pins for frequency expansion instead of switches? If so what is so rare about them? What is the switch contact configuration?
Nah; it is for the tx/rx shift.
It is just that the 858 chassis use a relay instead of transistor tx/rx shift - is all.
TX/RX shift? For what radio or any radio with that chip that you want an offset on like for 10m repeaters etc.?
Oh OK. I am still at a loss as to why radios with the uPD858 PLL chip would be any different and require any switching of anything to do with the PLL. Usually switching is done with crystals in the different mixing circuits. I know the uPD858 is BCD encoded and not the normal binary scheme but then again it has been a loooong time since I dug around inside of a radio with one. I think the last was an old Navajo from R/S.
the PLL does not have any thing to do with the relay portion. the relay is just for the TX and RX of the radio. it is just that some of the 858 PLL radios were designed to use a relay . some mics have a switch on them for mechanical switching and electronic switching also.
The reason that the relay in the 858 chassis fails so often is because the audio output is switched from the speaker (in receive) to the driver/final (in xmit) through a contact set in the relay. With the speech clipper circuit in these rigs, there is a ton of audio anyway. But when people bypass the mike amp limiter and crank the modulation adjustment up all the way, the additional audio current literally fries the relay contact set. I've changed out relays where the phosphor bronze contact spring had actually turned blue from the heat. Leave the mike audio circuit alone, and you'll never have a relay problem.
- 399
- 399
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Good info 399. I recently picked up a 138xlr at a yard sale. The radio seems to be untouched and works great. I'm going to recap the radio as well as perform the upgrades advised on your web page, and leave the radio stock. Great stuff!
Think ill order a relay myself just in case.
Merry Christmas
OK now that makes sense. I have seen many radios that had relay switching,that is all they used in the early units, and could not for the life of me figure out WTF the type of PLL chip had to do with then relay type. The uPD858 was in vogue about the time radios started to make the change from relay switching to solid state switching.