Well..The Saturn Turbo is back on the bench and I need help!!!

[Lkaskel]

Hello Men,
I have a Saturn Turbo that I repaired and aligned with your help. It went back to the owner many months ago but unfortunately it has returned. The complaint was that is was off frequency. One challenge with this radio is that the owner cannot keep the cover on. He has opened it up many times trying to get "more" out of it. Because he has no idea what he is doing as well as he has no test equipment he turns everything under the hood. In fact, he cracked the slug in the AM xmit can. To troubleshoot the radio I began with just hooking up the radio to the scope and freq counter and checked it on xmit. It was way off. I decided to try an alignment from the beginning, The 1st issue is that I cannot get the 10.240 crystal to align. That is the 1st step in the procedure. It reads from 1 MHz to 60 MHz and never stops moving. Does anyone have any thoughts as to where I should begin? I did check for cold solder joints and other broken parts. Also, I am able to get a reading on my scope and am able to adjust L4 for the max VCO output.

Thanks as always!!!!

 

[Radioman1]

Some, may not want to hear this or like it. If the owner of the radio has such affinity to the golden screwdrivering of the radio that you repaired, that it is more than evident he has 'adjusted' the unit to death, I would send it back to him, charge him for the shipping and never look back. I would be up front with him and tell him never to send it back and to deal with the "off frequency' problem himself. Especially since he likes to screwdriver things so badly, let him repair it. Some people you can talk too, some folks must be slapped. Afraid you going to repair it once again and he will screw it up once again, you be stuck in a never ending cycle until you lose patience with it. Suppose my attitude comes from being an old Navy Chief for almost 30 years.

 

[Unit 75]

Re-solder the bottom of the 10.240MHz xtal and check it again

 

[nomadradio]

The PLL section of that radio has two phase-locked loops. They are in turn (surprise) locked to each other.

As a result, trouble in one loop makes the other one act wrong.

And vice versa. The divide-and-conquer method doesn't work so well in pinning down what's wrong. And if both loops have been screwdrivered, the water gets really muddy.

First time a customer did this to a radio with the "2950" pc board in it, I needed a couple of hours or more to get it back in control of the whole range of frequency coverage.

Got a little better at it the next few we saw. A little better.

That being said, you really need a (more or less) 50 MHz 'scope with the trigger set as described in the factory alignment procedure.

To eavesdrop on every stage of the PLL the 'scope should be rated more like 100 MHz. Not necessary if all that's wrong is just sabotage alone.

The thing to remember is that this radio "retunes" the narrow-banded 1st-RF and receiver bandpass stages by feeding the PLL's tuning voltage to varactors wired to those slug-tuned coils. If the PLL is out of lock, the tuning voltage will skew those coils so far the the tuning slug just won't peak like it should. The transmitter bandpass coils following the transmit-mixer chip are also voltage-tuned this way. The industry term for this trick is "track tuning". This is what makes these radios so much more broad banded than the 'Galaxy' type radios that use the EPT3600-xx series of pc boards.

Somebody (else) should develop and post a rescue procedure, to get the individual sections of the PLL's adjustments at least close enough to make it lock again. The way we have done it is more "by gum and by gosh" than it is by a checklist procedure. Depends on which slugs the saboteur chose to tweak. The ones that haven't been cranked won't be the cause of the trouble.

Wish I could be more optimistic, but that's been our experience with this particular fault.

73

 

[Lkaskel]

Some, may not want to hear this or like it. If the owner of the radio has such affinity to the golden screwdrivering of the radio that you repaired, that it is more than evident he has 'adjusted' the unit to death, I would send it back to him, charge him for the shipping and never look back. I would be up front with him and tell him never to send it back and to deal with the "off frequency' problem himself. Especially since he likes to screwdriver things so badly, let him repair it. Some people you can talk too, some folks must be slapped. Afraid you going to repair it once again and he will screw it up once again, you be stuck in a never ending cycle until you lose patience with it. Suppose my attitude comes from being an old Navy Chief for almost 30 years.

Radioman, I don't disagree with you at all. I told the owner that I would give it a good shot but I will not loose myself in it. Also, I do charge a little bit to repair radios so I would be compensated. It was interesting that at 1st he told me that he did not know what happened. When I opened it and found the AM and SSB power maxed out he did admit to that much. When I found the broken AM slug, well, I am still waiting for the truth.

 

[Lkaskel]

The PLL section of that radio has two phase-locked loops. They are in turn (surprise) locked to each other.

As a result, trouble in one loop makes the other one act wrong.

And vice versa. The divide-and-conquer method doesn't work so well in pinning down what's wrong. And if both loops have been screwdrivered, the water gets really muddy.

First time a customer did this to a radio with the "2950" pc board in it, I needed a couple of hours or more to get it back in control of the whole range of frequency coverage.

Got a little better at it the next few we saw. A little better.

That being said, you really need a (more or less) 50 MHz 'scope with the trigger set as described in the factory alignment procedure.

To eavesdrop on every stage of the PLL the 'scope should be rated more like 100 MHz. Not necessary if all that's wrong is just sabotage alone.

The thing to remember is that this radio "retunes" the narrow-banded 1st-RF and receiver bandpass stages by feeding the PLL's tuning voltage to varactors wired to those slug-tuned coils. If the PLL is out of lock, the tuning voltage will skew those coils so far the the tuning slug just won't peak like it should. The transmitter bandpass coils following the transmit-mixer chip are also voltage-tuned this way. The industry term for this trick is "track tuning". This is what makes these radios so much more broad banded than the 'Galaxy' type radios that use the EPT3600-xx series of pc boards.

Somebody (else) should develop and post a rescue procedure, to get the individual sections of the PLL's adjustments at least close enough to make it lock again. The way we have done it is more "by gum and by gosh" than it is by a checklist procedure. Depends on which slugs the saboteur chose to tweak. The ones that haven't been cranked won't be the cause of the trouble.

Wish I could be more optimistic, but that's been our experience with this particular fault.

73

Nomad,
Thanks as always for your helpful responses. I was wondering if it were possible to mis-align this radio so bad that it would cause this issue. I will attempt to re-align it and get the ref oscillator back to working correctly.

Thanks again!!

 

[Lkaskel]

Oh well. Its official. I gave up. I never could get the 10.240 crystal to align. Next up.....