Who's the PLL/synthesizer expert here?

[Todd, KA1KAQ]

Frank 'GFZ talks about this torturous stuff from time to time. It makes my head hurt.

I have a solid state rig from the 80s with a lock up issue, or failure to do so is more accurate. Displays the frequency but just beeps. These rigs are not my cup of tea, better to pay someone else than to make it worse. I have the 3" thick service manual with it for pure reading enjoyment. Any takers?

[Pete, WA2CWA]

How about telling us what the rig is

[Todd, KA1KAQ]

Ooops! Sorry about that. It's a KWM-380 and it needs a new home, fixed or broken. The experts have told me that it takes about $10 worth of parts and a little time to fix it, but as soon as I pulled the lid off, I thought better of it.

[WA1GFZ]

Todd send me a pm  I bet I can fix it if it isn't a weird IC  gfz

[w3jn]

I'll give ya $50 for it 

Seriously it's most likely having to tweak the VCO coil just a bit to get it within lock range.  Find the synth board and you'll prolly see in the manual somewhere to check the VCO voltage for a specific dialed in freq.  Just adjust the core of the VCO coil to read that voltage and yer done.

Of course that *may* not be the problem, could be more serious.  But I have a Collins 651S1 that had the same issue and that fixed it.  15 minutes and most of that was pulling the board in and out to adjust the VCO coil in increments as well as tack soldering a wire to the VCO test point (this stupid thing requires extender cards to properly fix).

[WA1GFZ]

First you have to know the failure mode. If the synthesizer locks at one end of the band I agree with John. Buuuut that would be easy. I would look at the VCO control voltage and the two inputs to the phase detector to see if the control voltage agrees with the phase detector inputs. It could be as simple as the divide by n counter getting bad data. I don't like to tune inductors unless I'm sure they need adjusting. Inductors don't usually change over time. Then there is the loop filter. one bad cap and you are not going to lock.
Todd made the best choice. You don't know what your doing stop and ask because you can cause more damage messing around. Like probing Lincon's head for a hunk of lead. 
If I remember the 380 has a first if around 40 MHz and the synthesizer runs 40 to 70 MHz. Schematics will make it easy as long as there are no sealed cans or weird parts. I have not seen schematics on the 380 in many years.

[w3jn]

Yup, ya needs 2 things to make a synthesizer work - the reference signal and the VCO signal.  Now each of those is divided down and compared in the phase detector.  The DC output of the phase detector is what controls the VCO.  The KWM-380 is a multi-loop synthesizer, IIRC.  I think the freq is higher than 40-70, IIRC it's more like 80-110 MHz but it's been a while since I've dug into one.

Get a scope-a-dope on the gozintas and gozoutas of each phase detector and compare with what the manual sez.  You'll soon see which synth is crapped out and, by the missing (or incorrect) signal, be able to track it back thru the dividers, etc., to see where it goes missing.

[WA1GFZ]

Ah multi loop. Good thing you have schematics.

[Todd, KA1KAQ]

Yup, ya needs 2 things to make a synthesizer work

Actually, you need a third thing called ability. When it comes to newer gear with teensie, easily-zapped parts, I have none. Just reading what yous guys are saying makes me dizzy. If I did fix it, it would only mean I broke it even more first. That's my relationship with dark, cold gear.

It's a rather time-sensitive matter because I'm selling the rig to finance another project. I have several folks who'll give me back the $1800 I paid for it (yes, I bought it broke'd, in hopes of getting it fickst). In working condition it's easily worth another grand plus. I'm just lacking the time.

BTW, for anyone who's wondering why the guy who said he'd never own a solid state rig has one (broken, at that), it's because I listened to the folks who said 'you need at least one new tubeless rig or the universe will fold into itself and create a black hole, like your radio room'. And I believed them.

PM enroute, Frank...

[WA1GFZ]

Todd,
Knowing your limits is a very smart move. A hack job attempt at a repair can cause a lot more damage in a rig like that. Let's hope the guy before you was as smart.

[w3jn]

KWM 380s respond best to repairs when threatened with a huge soldering copper heated in a gas furnace.

[WA1GFZ]

John,
Remember the 4x4 guy on premium with 651 synthesizer problems?
He had it down to one of the sealed modules and was bummed and was looking for a new board. I gave him some ideas on how to get inside the soldered shielded boxes and about a week later he reported
it was a simple fix insided the shielded box. Sometimes you are right to haul out the big one.
I use a butane tourch to take crystal filters apart. I just fixed a nice Racal 400 hz filter with a loose ground screw. I added a few jumpers so all screws don't have to be tight for a complete ground sustem inside the filter.