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Magnum Delta Force USB Issue

Ghibli69 said:
From scheme 207-208-209 are 1ss135
Click to expand...
And they are simple Schottky type for switching (not varicap stuff so they don't tune - just steer)...

The Vari-cap which is D140 - may have a YELLOW band on it denoting CATHODE and it's special purpose.

On this Service Manual shot, earlier versions use a TO-92 case...See below...
DeltaForceMagnum.jpg
 
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I measured the diodes 207,208,209

D209
measures cathode side
AM = 4,64v
FM = 4,62 v
USB = 8,10 v
LSB = 8,08 v

measures anode side
AM = 0v
FM = 0 v
USB = 8.9 v
LSB = 0 v



D208

measures cathode side (yellow marker) :
AM = 4,63v
FM = 4,61v
USB = 8,11v
LSB = 8,11v

measures anode side :
AM = 0v
FM = 0v
USB = 0v
LSB = 8,86v

D207

measures cathode side
AM = 4,64v
FM = 4,58 v
USB = 8,13 v
LSB = 8,11 v

measures anode side
AM = 5,44v
FM = 5,41 v
USB = 0 v
LSB = 0 v

i think lsb and usb are inverted from schema
 
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I measured the diodes 199 and 201
D199

AM = 0 v
FM = 0 v
USB = 8,15 v
LSB = 8,15 v

D201

AM = 0 v
FM = 0 v
USB = 8,14 v
LSB = 8,14 v

Does anyone know what is the equivalent of c111 ?
Thank you
 
I measured the diodes 199 and 201
D197

AM = 8,21 v
FM = 8,17 v
USB = 0,13 v
LSB = 0,03 v

D198
AM = 8,20 v
FM = 8,17 v
USB = 0,12 v
LSB =0,03 v


Immagine.png

I think the problem is here, in the red area
 
Another problem, in USB and LSB with the mic gain closed the rf-meter rises near 9+ and the external wattmeter marks 15 watts in the absence of modulation only by pressing the ptt. Another strange thing that rotating the rf power in usb and lsb varies the power from 0 to 30 watts, which should happen for am and fm.
Any suggestions ?
Thanks
 
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Recheck all rear panel soldering joints - a cracked solder joint can cause what I'd call an "ultrasonic" squeal - caused by a failed ground return. The Mic gain may go into "squeal" causing this. Heck, can even be caused by dirty potentiometers - open substrate caused by dirt between the wiper arm of the pot to it's carbon composition substrate.

This may mean more problems down the road, so you may need to think about doing a re-capping process - replace all the old Electrolytic caps with new ones of the same capacitive value with one level higher in working voltage.

e.g - 10uF 16? - Replace with 10uF 25V (or greater) as long as the package outline (READ:SIZE) allows for it.
 
Ghibli69 said:
Sonoma do you have an e-mail address of the magnum ?
Thank you
Click to expand...

Sam Lewis passed away several years ago and I think his son is trying to keep things going. The number for RF Limited/Palomar is 1-877-624-6869. Last summer I ordered a replacement mic and thumb screws over the phone for a Magnum 1 radio. That number should still be good. At one time the Radio Shop in Ontario,CA was the factory service center for Magnum radio's.
 
Thanks for the help, I normally change all electrolyte capacitors on old radios (ept3600). This radio seems to me recent I think of 2000, however, all the electrolytic changes and I fix all solder joint starting from the back of the radio.
i'll let you know
 
If you have access to Newsgroups, like rec.radio.cb - I did up a review of the Delta Force, I have their earlier version of the board that had a Foil trace "Mistake" that many jumped all over the place about. It didn't bother me as much for m y issues were around how a radio can inject more noise when you TURN ON ANL or NB than you had with it off.

But once I ironed out the problems - the radio did ok.

But I am speaking from experience - mine did not hold up well in a SUV environment and gravel roads too well - that was in early 2000's. This platform came out about the same time Emperor Radios TS-5010 and the TS-3010 came out so all three during that "flat panel - push-button" era can give you an idea of expected problems with joint failures as well as the age timeline - you may have some work ahead of you to keep it going.

ADDED (Not a Tirade but think of it as a thought-provoking list of events that may occur in the worse possible order)

The radio came to me in one piece but I had to fix several cold soldering joints right out of the box to make the receiver quiet again.

The NB/ANL issue was partly caused by the assembly issue of loose case screws - ground plane noise issues - no big deal, until you decided to put the case covers back on again. The Case to Chassis plumb - was sprung! Meaning the case covers weren't exactly square to the chassis and of course, the Chassis is made from Aluminum and not steel. Making the mating surface alignment issues amplified - which the covers are made of steel and if not square you ran around with a radio with only a few screws holding the covers in place. Kinda "cheap" for a radio that cost me +$300 back then. This also posed a problem with the main PCB and chassis grounds too. Affected the ability for the main PCB board to handle the torque caused by the forced realignment of the case/Chassis to board and once several weeks had gone by - the problems with fatigue of the stress on the soldering joints came thru and the radio then got pulled and sat on a shelf for the rest of it's life...

So mine didn't last long - but being it was constructed the way it was started an adventure into the Electronic switching endeavor the radio uses - which now many are arriving as standard - which fails me in believing that the days of discrete are going to stay - instead we are becoming extinct. I began to start looking into other avenues of radio including what Ten-Tec offered as a means of "electronic" switch panels I would have liked to have tried this method with other radios - but that evaporated when Ten-Tec got sold and absorbed or just plain failed defunct...Kinda killed the dream of ever even going to the next level with this - now China has received our support for this because many that whom would have learned about the radio and theory are simply buying the cheap stuff and letting the rest of those trying to maintain a standard of living for those whom enjoy the older platforms (discretes) - screaming for help with supplies and singing "Who's Gonna Fill Their Shoes?
 
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I agree with you, for hobby I like to buy old cb radios to be repaired to understand how they work, in my small collection I have several radios
superstar 360 fm
president grant
prasident jackson
superstar 3900
superstar 3900F
Ranger2950
galaxy uranus (this too has been badly designed has many problems)
etc.
The Mgnum delta force has always attracted me for its aesthetics, so I bought one, but I never imagined it was so bad. Anyway, I'll try to fix it.
Another thing that I noticed and that on the wiring diagram the part of the diodes that go to the quartz x103 the usb and the lsb are inverted.
Surely I will ask for some other advice,
 
Welcome to Magnums' way of doing things. (Back then)

As said earlier - the thing is Negative Ground Only - which may not matter or become the bane of noise pickup.

The earlier version of this radio used a dual gate FET RF Front End amp similar to what Cobra 148 and Grant XL's used for their IF mixers, in an attempt to make the RF amp work similar to a Pre-selector/attenuator to reduce imaging problems this chassis develops along certain specific receiver section - like Birdies. Fine, but the original board I had, they silkscreened a transistor part - like the 1674, but what they put in on the bottom of the board, a 4-legged beast that made me go back to the original design of 3-legged transistor. With that redesign, it had it's own issues but receiver side worked better because the RF amp worked more like impedance matching and buffer than a IF amp filter and preselector they tried to squeeze in there.

Only that "Birdie" problem is an inherited artifact of the Xtal synthesis that goes on in there. Several areas of the board need to stay isolated from the others so they tried various methods of communication including the CPU controlled "Switchyards" but they seem to be more like antenna arrays for that IF imaging problem to propagate to other parts of the board thru the power supply buss feeds.
 
All the electrolytic capacitors have been replaced, almost all the solder points have been rebuilt. The radio initially doen't shows the defect, the wattmeter in usb and lsb measures 0 watts. After a while the radio is switched on the defect appears again, it feels like a larsen effect. in usb / lsb. The wattmeter in the absence of modulation with all the mic gain closed starts to measure 1 watt, 2 watt, 5 watt, 15 watt.
 

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