hi guys.
i hope bernie sees this.
i have a VHF R2 RF tray that seems to have a problem.
when conducting the alignment on the RF tray, the first step is to tune the injection filter.
this is accomplished by tuning L7, L8 and L9 on the RF deck (injection filter) for MAX on Meter #3. No sig gen is used (per the book) just power up the station and plug into meter #3....
but i don't see ANYTHING on meter #3... 0 ua.... even after adjusting all three poles of the filter from all the way down to all the way up.
anyone have some troubleshooting?
i have the detailed UHF manual, but my VHF manual (borrowed from alex) is the "new and improved we don't explain everything in detail" version!
help!
oh, the the injection amp (where L7, L8 and L9 are) is still available... over $200 from M.....
doug
MSF5000 question
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MSS-Dave
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Nand is on the money. I don't have my manual here but you need 38 uA (at least on 450/900 stations) of VCO drive to get TX/RX lock and get anywhere with the rest of the alignment. If Bernie doesn't post before Monday PM, I'll post the complete alignment if you like. BTW, is this a repair (doesn't work) or are you just moving the frequency?
Dave
Dave
hi guys...
thanks for the replies.
the VHF MSF has NO ADJUSTMENTS for the VCO's.
they either LOCK or don't.
this was a re-program/re-tune, from 150ish to 146ish
within the bandsplit - no forced out-of-band stuff.
i think the way the manual is written is incorrect.
per the alignment procedure, you:
tune the image filter
tune the preselector
i think this is backwards - to tune the preselector, you have to have a sig gen to provide the rx freq input for peaking / nulling the preselector.
however, the image filter alignment (using Meter #3 on the DMP and plugged into the Rx RJ45 spot) DOES NOT state to use a sig gen or anything....just to ACC DIS the station.
this is what i am going to try this PM:
align the preselector using the book (sig gen / RF millivoltmeter on R2001/d)
then i am going to try again to tune the image filter, except this time i am going to USE THE SIG GEN to provide a signal into the Rx.... CONTRARY to what the book sez
doug
the VHF MSF has NO ADJUSTMENTS for the VCO's.
they either LOCK or don't.
this was a re-program/re-tune, from 150ish to 146ish
within the bandsplit - no forced out-of-band stuff.
i think the way the manual is written is incorrect.
per the alignment procedure, you:
tune the image filter
tune the preselector
i think this is backwards - to tune the preselector, you have to have a sig gen to provide the rx freq input for peaking / nulling the preselector.
however, the image filter alignment (using Meter #3 on the DMP and plugged into the Rx RJ45 spot) DOES NOT state to use a sig gen or anything....just to ACC DIS the station.
this is what i am going to try this PM:
align the preselector using the book (sig gen / RF millivoltmeter on R2001/d)
then i am going to try again to tune the image filter, except this time i am going to USE THE SIG GEN to provide a signal into the Rx.... CONTRARY to what the book sez
doug
You are correct about the lack of VCO tuning in a VHF station. So the VCO should at least be locked to the correct frequency before you can do any of the other tuning. And the injection filter should be tuned first and measured on “meter 3”, the mixer local oscillator level.
The reason is that the all the other tuning is done using the “meter 2”, the IF level. If the “meter 3” reading does not exist, it can be assumed that there is NO local oscillator signal and therefore also no IF signal to measure.
Provided that you DO have a “meter 3” reading because you have a local oscillator signal, you should now tune the image filter first as the book says. The image filter is located between the point you are injecting the signal into and the mixer.
What happens here is that you are injecting an on frequency signal into the last pre-selector cavity (the one farthest away from the antenna connector). And in order to see the tuning on “meter 2” (the IF level), the image filter needs to be able to pass this signal first. If it is not tuned at this point, no signal or very little will ever reach the mixer and IF.
Continue with tuning the rest of the pre-selector cavities as per manual.
I hope that you are using the correct signal injection cable designed for this procedure. It is a small coaxial cable that is inserted in the pre-selector cavities for signal injection.
Nand.
The reason is that the all the other tuning is done using the “meter 2”, the IF level. If the “meter 3” reading does not exist, it can be assumed that there is NO local oscillator signal and therefore also no IF signal to measure.
Provided that you DO have a “meter 3” reading because you have a local oscillator signal, you should now tune the image filter first as the book says. The image filter is located between the point you are injecting the signal into and the mixer.
What happens here is that you are injecting an on frequency signal into the last pre-selector cavity (the one farthest away from the antenna connector). And in order to see the tuning on “meter 2” (the IF level), the image filter needs to be able to pass this signal first. If it is not tuned at this point, no signal or very little will ever reach the mixer and IF.
Continue with tuning the rest of the pre-selector cavities as per manual.
I hope that you are using the correct signal injection cable designed for this procedure. It is a small coaxial cable that is inserted in the pre-selector cavities for signal injection.
Nand.
batdude wrote:well, i am baffled.
meter #1 = 25ua
meter #2 = 10-11ua
meter #3 = zero
i am using the correct signal injection cable (in my msf tool kit)
no adjustments of the image filter (L7, L8 and L9) affect meter #3.
no adjustments of the image filter L10, L11 affect meter #2.
i tore apart the RF tray today, took the uniboard out, took the image filter out, took the preselctor off... nothing obvious.
it would have been nice if the "newer" service manual at least had the sheets showing where the test points are.
doug
From your PM above, it looks like you have no Local Oscillator (RX VCO) signal going to the Injection Amp or nothing coming out of the injection amp or nothing coming out of the Mixer. It is also possible that there is a problem with the “meter 3” circuit that prevents you from getting a reading. But if that were the case, you possibly would have noticed some change on “meter 2” while tuning the filters.
Anyway, if “meter 3” reads zero, you can not tune the front end and no doubt not receive either.
The complete string from the RX VCO up and including the Mixer are suspect. See if you can trace the VCO signal through there with a spectrum analyzer with a probe on it or a RF voltmeter as my second choice.
I only have a UHF and an 800 MHZ manual here. The UHF manual seems to have been put together by idiots. A lot of stuff is either not in there or only partly in there. But the over all block diagram is the same for all stations.
Sorry for posting your PM here, but there are experts around here when it comes to MSF5000 stations that can help you better. I am not one of them.
Nand.
My two bits worth:
I would suspect that your problem is this:
The injection filter can grow metallic "wiskers" on it's interior walls, causing the filter to detune.
The fix is to pry the two covers off the bottom of the filter, and clean it with contact cleaner. I rub the walls with a tooth pick to insure that the"wiskers" are removed. Some of these look as if a metallic spider was at work inside. This can also happen to the VCOs on the UHF, and 800/900 models.
Another possibility is that the injection amp is defective. You can easilly measure the injection at the RCA connector to the filter.
The the mixer diode on the front end could be defective.
I have to agree about the manuals!
I would suspect that your problem is this:
The injection filter can grow metallic "wiskers" on it's interior walls, causing the filter to detune.
The fix is to pry the two covers off the bottom of the filter, and clean it with contact cleaner. I rub the walls with a tooth pick to insure that the"wiskers" are removed. Some of these look as if a metallic spider was at work inside. This can also happen to the VCOs on the UHF, and 800/900 models.
Another possibility is that the injection amp is defective. You can easilly measure the injection at the RCA connector to the filter.
The the mixer diode on the front end could be defective.
I have to agree about the manuals!
Aloha, Bernie
I have a friend who bought a VHF MSF5000 by my recommendation. The seller claimed that he couldn't tune it because his sig gen died, and made an appropriate adjustment in price. Naturally when my friend got it he tried following the tuning instructions. Zero meter reading on pin 3, no matter what he did. We seemed to have mixer amp activity and he could see a signal going into the front end from the mixer. He had run all five mixer/injection coils from one end to the other with absolutely no effect.
Finally he pulled the front end and popped open the press-in covers. Looked like a bird's nest inside. Talk about whiskers. He sent me some pictures that were just unbelievable. Most of them were in the mixer section and had shorted out some or all of the injection/mixer coils, rendering them untunable. He cleaned everything thoroughly and reassembled in reverse order.
Plugged his metering set into the RX jack and set it for pin 3. Still zero. Then he started tuning L7. All of a sudden he had a few microamps on the meter! Nothing big, but definitely movement. He went to L8 and got the meter up to 20 uA. Then went to L9 and got it up past 30 uA. He went on to complete the front end alignment and the receiver now opens squelch around 0.15 uV.
We think that the seller's sig gen might have been OK but the receiver mixer section had gotten shorted out. If it wasn't that way when it began its trip to the buyer, then the fact that the unit was placed on its back in the trunk of a car could have caused some of the longer whiskers to move and short things out where they had not been a problem before.
I don't recall if we found this info on the BBS before or after the whiskers were removed. Searching the web for "tin whiskers" will get you a really nice article/site at NASA and they have much better pictures there. Worth reading.
My UHF MSF5000 has not exhibited this problem yet, luckily, but now I know what to look for should it suddenly die some day.
The whisker problem could have been totally eradicated if the mixer coils had been coated with something like varnish or lacquer, or had been wrapped with some form of insulation like Teflon or even PVC plastic. This would keep the whiskers from shorting out the coils no matter how big they got. Of course, there still could be some detuning effect, but that could at least be compensated for with a slight bit of retuning every once in a while.
Definitely an experience to behold.
Bob M.
Finally he pulled the front end and popped open the press-in covers. Looked like a bird's nest inside. Talk about whiskers. He sent me some pictures that were just unbelievable. Most of them were in the mixer section and had shorted out some or all of the injection/mixer coils, rendering them untunable. He cleaned everything thoroughly and reassembled in reverse order.
Plugged his metering set into the RX jack and set it for pin 3. Still zero. Then he started tuning L7. All of a sudden he had a few microamps on the meter! Nothing big, but definitely movement. He went to L8 and got the meter up to 20 uA. Then went to L9 and got it up past 30 uA. He went on to complete the front end alignment and the receiver now opens squelch around 0.15 uV.
We think that the seller's sig gen might have been OK but the receiver mixer section had gotten shorted out. If it wasn't that way when it began its trip to the buyer, then the fact that the unit was placed on its back in the trunk of a car could have caused some of the longer whiskers to move and short things out where they had not been a problem before.
I don't recall if we found this info on the BBS before or after the whiskers were removed. Searching the web for "tin whiskers" will get you a really nice article/site at NASA and they have much better pictures there. Worth reading.
My UHF MSF5000 has not exhibited this problem yet, luckily, but now I know what to look for should it suddenly die some day.
The whisker problem could have been totally eradicated if the mixer coils had been coated with something like varnish or lacquer, or had been wrapped with some form of insulation like Teflon or even PVC plastic. This would keep the whiskers from shorting out the coils no matter how big they got. Of course, there still could be some detuning effect, but that could at least be compensated for with a slight bit of retuning every once in a while.
Definitely an experience to behold.
Bob M.