Omnitronix Schematics (find brick wall, pull head back, release, repeat)

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ChuckG
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Omnitronix Schematics (find brick wall, pull head back, release, repeat)

Post by ChuckG » Sun Aug 21, 2016 12:23 am

Oh dear Lord, why....why....

The step start circuit on our Omni 1kW decided not to. Nothing, absolutely nothing in the manual, or the drawings, or the zip archive of every known Omni schematic Fossil sent me shows the Power Supply circuitry and how the step start is configured.

It isn't the usual setup where line voltage through the resistors rises and pulls in a second coil, which then bypasses the resistors, oh no...no no.
It's a voltage sensor, an op amp/driver and some other undocumented logic circuits that disappear into a harness full of identical, un-numbered wires before somehow arriving at the relay coils.

Relay #1 would pull in, transmitter would start but, relay #2 did NOT pull in to bypass the step start resistors. A few seconds later relay #1 timed out and the rig shut down. Repeat, repeat.

I pulled the relays and cleaned the contacts. Holy hell it started working again. I have no idea if part of the control logic is routed through one of the relay contacts, or if the wind merely blew from the correct direction and I'm on borrowed time. This is where a drawing of that circuit would be really useful.

Anybody have one?
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Chuck Gennaro
Central Wisconsin

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RGORJANCE
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Re: Omnitronix Schematics (find brick wall, pull head back, release, repeat)

Post by RGORJANCE » Sun Aug 21, 2016 6:34 am

You should know, after all these years, that "the wind never blows in the right direction", and the payment is immediately due "on borrowed time"!

I find that a well placed "love tap"---WHAP!!! is a good start. :evil:

On the brighter, you can clean the contacts on a relay, but not on a dip chip. :lol:

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TPT
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Re: Omnitronix Schematics (find brick wall, pull head back, release, repeat)

Post by TPT » Sun Aug 21, 2016 7:25 am

" you can clean the contacts on a relay, but not on a dip chip. :lol:"

Brings back some not so fond memories of those Texas Instruments chips made in Malaysia. The ones with the leads that were not silver-plated properly--and would rust away!

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KPJL FM
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Re: Omnitronix Schematics (find brick wall, pull head back, release, repeat)

Post by KPJL FM » Wed Aug 24, 2016 7:29 am

RGORJANCE wrote: On the brighter, you can clean the contacts on a relay, but not on a dip chip. :lol:
Fossil
In my case, contacts on my dip chips are my dentures.
Trim to fit, paint to match, tune for minimum smoke.

ChuckG
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Re: Omnitronix Schematics (find brick wall, pull head back, release, repeat)

Post by ChuckG » Fri Aug 26, 2016 3:24 pm

Just to follow up on this, in case anyone else runs into it,
The way the step start circuit functions is as follows, courtesy of Mike Patton:

Transmitter ON button is pressed
A one-shot timer is triggered that pulls in K1 for ten seconds, connecting the AC line to the 300V transformer through a step-start resistor.
The PDM generator is still muted, thus no load on the supply, which should rise to 300V.
A comparator monitors the output of the 300V supply, if it reaches 300V before K1 times out, it pulls in K2, bypassing the step start resistor.
So..... now I know why cleaning K1 contacts helped. The supply was only rising to 200V or so before it timed out.
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Chuck Gennaro
Central Wisconsin

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