Batboard

Hey Gang,
Here's one for the MSF crowd. I've got a CXB station here that I'm setting up for someone. The station was aligned about a month ago (alignment was straight forward) and he just recently got the controller to me. I wanted to re-verify everything before I interfaced his controller. I powered up the station and couldn't get a lock on the tx vco. The diagnostic panel was reading roughly 48 micro-amps. I tried retuning the vco with absolutely no voltage change whatsoever. I swapped out the vco with a known working one and had the same results. I reset the station and on the 3rd reset it came into align and the voltages went normal. Since then I've only been able to make it fault once and after a couple resets it straightened out.
I do have to add when the station faults its only happening on the tx vco, the rx vco shows normal with just the dreaded E47 error code appearing in it self-diagnostics.
Any ideas?
Doug

I'd suspect connection problems on the Uniboard.

Open it up, carefully pull the Uniboard upward about 1/2 inch. It can be flipped over by raising the front and pivoting it at the rear where all the cables are attached. Pull each connector off and put it back on again. They should all be snug. Put the board back. Pull and reseat the cables going to the VCOs and anything else you can see.

If the problem returns, then it's time to troubleshoot the transmit synthesizer area of the Uniboard.

Also reseat the flat cable going from the SSCB to the RF tray. Pop it out and put it back in again.

Bob M.

Hi Bob,
I think my search is going to have to go a bit further, I've pulled the uniboard and checked and cleaned all the connections and made sure everything was snug. I powered it this AM and its currently in a fault state and I can't get it to reset, perhaps now I'll be able to track it down, I hate intermittent problems.
Doug

The manual says to reprogram the SSCB or repair/tshoot the VCO.

I've seen stations that throw an error code when they first finish the self-tests, but by the time you go back and look at the display again, it shows "11" and the error is gone. Some VCOs are just slow.

I'd measure the steering line voltage feeding the VCO, to see where it is, although it's probably similar to what you're measuring on M5 on the transmitter. Then try to measure the output frequency to see if it's way low. If I recall, the SL voltage goes high to raise (or try to raise) the output frequency.

It could also be the circuit sampling the VCO output. RCA jack, plug, cable, etc. Since the VCO operates at 450 MHz, you'll need something that's sensitive at that frequency to see where the signal is being lost.

I trust you have manuals/schematics.

Bob M.

For the benefit of our search engines and those following this thread the problem was resolved. Once again all of this turmoil was created by the dreaded whiskers growing within the VCO's. I've learned that looks can be deceiving as well. I say this simply because I had pulled the VCO's apart and glanced at them and they appeared normal but in actuality they weren't. With the prodding from Bob (a.k.a. kcbooboo) I gave them a thorough cleaning and re-installed them and everything started coming back together.
My thanks to those who helped me with this and for your help, I'd like to pass along a stock tip: Start dumping your stocks in antacids
Doug

I just worked on an MSF that had a bad ribbon cable. This was due to it being pinched between the chassis and the rail on the right side. It caused all kinds of errors and once replaced, the problems went away.

On a related whisker note, I have a problem with three different VHF MSF units. I can't get a meter 3 on the receiver to tune the injection filter and yes, I am changing frequency.

Is this also subject to whiskers? Is this common?

I have not had one do that before.

George

George,

I have seen the problem in the UHF injection filters a few times so I suppose it is possible in the VHF station as well. It may be time to pop one out and do a cleaning to find out if it helps.

L.E.

Yes, the whisker problem can and did happen to a friend's VHF station. Any plated assembly could grow whiskers, but the dull finish on some assemblies seems to mean things aren't tin-plated and won't grow whiskers. I found that the insides of my VCOs were a dull finish and they were as clean as pie.

It's not hard to get to the injection filter, and once unplugged, the metal covers on the back can be pried out.

I had a UHF station with no M3 reading at all. Turned out to be a bad factory solder connection of the output tap on a coil. I could see the blob of solder with a concave receptacle where the wire had been, but it obviously pulled away and wouldn't let the RF bridge the gap. A quick touch with the soldering iron fixed it right up. The tuning is hard enough on that assembly when moving it more than 6 MHz, and an open connection didn't help. No whiskers inside though; that was the first thing I checked for.

Bob M.

George,
What was even stranger is I swapped out the vco as well with one of my quote unquote working spares and had the same symptoms. I had a problem once before as you described. I remove the injection filter cleaned the five tunning screws and the 4 rca connectors and with that everything worked out. The down side is they're a pain in the butt to get out. I'm not sure if you've done MSF's before or not but I've noticed with a frequency change that I usually have to go back and forth between L7 and L8 before I start seeing any major changes on the diagnostic panel. I'm sure everybodys mileage is different but that's just my experience with them.
Doug

Yes, with a big frequency change, the mixer coils require careful tuning to get that first glimmer of rise on M3. I've had to turn each one 1/2 turn, in sequence, to get the slightest indication, but once you get that 1/4 microamp, the rest tune easily and it's all downhill. It's just one of those things you have to deal with.

When mine failed to give me any M3 even after a lot of tuning attempts, that's when I pulled that assembly out and hooked it up to the spectrum analyzer. I should have seen about 3dB loss across the injection filter, but instead I was getting almost 60dB. That's when I found the broken connection. Once that was fixed, it was easy to tune roughly on the spectrum analyzer. Then when I put it back into the station, it tuned up immediately. Of course it's a lot of work to remove that assembly just to tune it externally, but the tuning was immediately apparent using that method.

Bob M.

Okay, normally you all know that I am not this lazy, but since it's very late for me and I am exhausted, I'll ask anyway...

1: What should the injection frequency be for a receive channel of 144.61? This is a range 1 station, 135-156 MHz.

2: If I were to take a range two station down, does the injection flip over like in a Micor receiver or does it just continue on down?

3: Has anyone tried pulling a range two down below 146.000?

The VCO bears a strong resemblence to an X9000 VCO and looks as if a few staps could be added back in to pull it a ways down.

I'll try the injection filter thing this weekend. I have a really difficult time believeing I have three bad stations. Must be the alignment.

George

To get at your injection filters you must first remove the uniboard and all connections then there are about 12 screws holding your filter assembly to the chassis. Once you have the filter assembly out you'll see the injection filter it sits on the upper left side. The injection filter is attached to your filter assembly via 4 rca connectors mounted rigidly to both respective components. You should be able to get under it with a small screwdriver and gently pry upwards. It is important that when you remove it that you bring it straight up as there is a metal loop that drops into the filter.
As far as the range of your vco's its probably anyones guess as mileage varies. Its easy enough to find out if you can get a lock light and 38ua my guess is it should be fine. I would have to guess that its going to be a little fussier than normal to adjust.
If I've missed anything hopefully kcbooboo or xmo will jump in to help.
Doug

According to my VHF manual, the transmit VCO operates from 146-174 (R2) or 132-258 (R1). The receive VCO operates from 135.3-163.3 (R2) or 121.3-143.7 (R1). There is no adjustment on either VCO. The IF on VHF stations is 10.7 MHz, so the receive VCO operates that much lower than the incoming carrier signal.

Obviously there is no "flip" around some magic frequency, however people have reported that you can try to program a receive frequency that would put the VCO on the high-side of the IF, and try to tune the mixer coils appropriately.

There probably aren't too many component differences between the two ranges. The UHF VCOs have factory-trimmed capacitors etched on the VCO circuit board; you could probably use some solder or conductive ink on it and lower the frequency if necessary. As it is, the station might go down that low; try it and see.

Bob M.

Yes, I am showing my lazying again because this job is really getting old and driving for 1.5 hours to work is dragging on me, here we go again.

Okay, got the part about VCO operating ranges. Many thanks.

Since both VCOs (range one and range two) are operating in low side injection, I would take it that there is nothing magical about the way the frequency is being loaded into them.

With this assumption having been made, there should then be no reason why we can't set up a range two station as a range one station with the only concerns being IF the VCOs lock. If a range two station is defined as range one, nothing should happen except hitting the VCO rails and like what was said above, a little conductive ink or solder bridging should resolve those gaps.

There are problems with the X9000 where the range of the radio directly impacts the programming of the VCO on a per channel basis. For example, some RSS will allow lower band limits on a range two VCO. But if you use that range on a range one VCO, some channels may work and others may not.

Also, while this is an observation for the moment, my range one VCOs in VHF are not at 38 microamps. The measurement is at about 25 or so at thsi point. Doesn't this current vary depending upon the point in the range?

George

The M5 reading on a UHF station, where the VCOs are adjustable, should be 38uA on the "tuning" channel, which is either the median or highest frequency in use. If you only have one channel programmed, which is typical for amateur use, then you would adjust the VCO for 38uA on that channel.

VHF VCOs are NOT adjustable. The steering line (M5) can probably range from 15 to 42. If it exceeds those values, the LOCK LED will probably turn off. If the VCO is grossly mis-tuned, the M5 line will be down below 10 or around 45. A lower reading indicates a lower frequency, so if you're running at the low edge of the band, the M5 reading will also be low.

There are/were some threads on here dealing with programming a receive frequency 21.4 MHz higher (twice the IF frequency) than what you really wanted, and using high-side injection. It's worth a shot.

Bob M.