Connex 3300 HP frequency problem

[Handy Andy]

PLL swapped out and still the problem?

Thanks for swapping out C101 - it's just cheap insurance.

I need some assurance though, that Pin 1 is the 8V and Pin 18 is the Ground and as you toggle the bandswitch if there is a sag in voltage - any flutter - because something is making the PLL think it's got a new frequency so it jumps to it.



WOW, ok, I don't know about anyone else but I'm still stuck on that Bandswitch that HI-LO - possibly having a "dead spot" and once it jitters - the PLL thinks it's something new...But if it's that uncommon - else we'd have a ton of service bulletins over the Band Switch and Hi-Lo all over the place...

I had a COBRA 148GTL-F that used a resistor (L9 stuff) on - back then - they're new RCI 8719 chip - and warbled like crazy, even power supply issues. rec.radio.cb NG My Malaria (Malaysian made 148's) L9 used 100ohm resistor - needed to be 10 ohm instead and replaced 1000uF with 100uF cap to reduce the "lag effects" caused by cap holding power supply line lower than average.

In looking above, I'm not sure of the AGE on that radio but I wonder if it needs to be recapped or have the regulator / power supply feeds gone over...

How's the soldering job up front on the main panel - everything ok up there?

:+> Andy <+:

 

[Crossbow]

Andy I have found something. When it jumps freq D105 and D106 in the matrix comes alive. Neither should be reading voltage and neither does when it is on normal freq but once it jumps freq both are reading 4.36 volts.

 

[Handy Andy]

Which side, banded or non-banded? Why - direction helps - because that may indicate IC6 - you fixed IC 7 - something is latching...so it is aware...Unbanded means something is sending voltage INTO the matrix from somewhere, but if it's only on the BANDED side - the inputs are faulty IC6 is what these go to - try replacing that 4008 instead...

:+> Andy <+:

 

[Crossbow]

Banded side. Going to replace IC6 now. Standby.

 

[Handy Andy]

(waiting with baited breath-reaching for a mint...)

 

[Crossbow]

And there she blows! Back working like it should be. Wow what a nightmare this has been. Should have replace 6 when I done 7 just for the heck of it. Live and learn! Thanks again for all your help buddy. I hope you have an awesome day!!!

 

[Handy Andy]

SYNOPSIS

Powered on, radio set to channel - but channels "changed" frequency - Channel Selector never changed.

Failed Adder INPUT on IC6 - PIN1 and PIN15

Ok, explains the "jumps" and the freeze too.

Truth Table only let certain Channels work.

Detected by testing Diode Matrix against ADDER pins. Banded and unbanded.


PDF's of common ADDER 4008 attached
Radio PLL swapped - no change.
Swapped Channel Selector - no change
Used Identical radio to verify test and voltages.
Resistor Arrays RA101 and RA102 - 47KX8 SIPP checked - normal...
Replaced IC 6 but both IC 6 and 7 swapped to determine.

:+> Andy <+:
Thank CB Tricks for the references.

 

[Crossbow]

Yeah where I kick myself in the butt for not checking the voltage while the problem was activated instead of while it was working normal. Could have saved a lot of time and found it from IC6 pins while it was acting up. Live and learn!

 

[Handy Andy]

I hope you don't mind the documentation of your procedure. It's not something you'd see out here and I was impressed you took the time to do this - and post results.

Back in the 70's and 80's there used to be a thing called Signature Analysis - it was a way to troubleshoot things when you didn't have the documentation from the designer. Knowing the parts, gave you the "outline" of what the device was to take in as input, process and present as output - if it was a problem - you had a means to diagnose and solve the problem - right down to the very logic-level or analog level and part that needed replacement.

A PDF is attached to help you, or the next guy - understand analysis - the paper deals more with analog, but even in your case - again you kept trying - and found the "leaky part" that upset the apple cart.

You had a "template" and the identical radio, that was what you compared to. Signature analysis is a lot like that. When all other avenues were tried, you had to then develop a method to check - and as you can see - nearly everyone here "blanked" on it. You kept trying - and when discovered, it was not impossible to realize, resolve and fix - for knowing that (in this case) the ADDER had a failed input, Short, reflecting output (like a shorted diode or transistor, no control of power flow) - signature analysis would have helped but not everyone has such a means or develop a method similar to what you did, anymore. The analysis part still required you to "back probe" the lines to find the short - as they (the ones that manufacture these chips) would have to do the very same thing when they test their devices before getting put out on the market.

So in a way, by practicing the result you get, is that; you helped the rest of the Forum to document the procedure and train others on what to look for. You deserve a lot more credit than you're giving yourself.

Give yourself a couple of Atta-Boys' - you deserve it.

:+> Andy <+:

 

[Crossbow]

Thanks for the kind words. Yes I am very happy you posted up detailed info for the next person that comes along with the same type of problem. This will make life a lot easier for them! Back in the day I see there use to be a lot of folks helping each other but now you see very little help if any at all. I am so glad your on this site and getting it back going like it use to be in the old days! I for one love watching, reading and helping! Yeah I keep a couple old out of date but still working radios laying around to use as a reference point as most all these type radio's are built on the same bases so it gives me something to cross check things with. Thanks again for all you do for this site and give yourself a couple pats on the back for being such an upstanding guy!

 

[nomadradio]

Got in the habit of treating these two chips like headlights on a car. When one of them goes bad, you change both. That's cheaper than futzing over the binary math to figure out which one has gone nutty.

Also have a policy of using sockets for the replacement. If some unexpected gremlin zaps a new 4008, the labor it would take to solder in in another one makes the socket really cheap in comparison. Besides, the heat stress to the foil pads will cause them to lift from the board the second time you remove one of those chips. If you're gentle, the foil pads nearly always survive the first time.

73

 

[W4KVW]

Well I picked up a 3300HP in some trading & I don't use Export CB's so I put it on my bench to test it out before selling it & no matter what channel I put it on my frequency counter reads around 24.389 mhz. but it jumps around in that area. The output power is great but I don't need a 12 meter AM/FM mono frequency mobile. I did not read all of the replies to this posting so maybe the answer is in them somewhere though the frequency issue is a bit different? If it's worth taking to the local CB Shop for repair I will take it so I may part ways with it very soon. I have the box & mounting bracket as well & now know why the last owner parted with it. Thanks for any input & God bless.

SIX-SHOOTER

 

[nomadradio]

It's a complete toss-up.

Could be that the problem is only defective solder connections on the main circuit board. We do see that a lot.

Could be that ten different folk have each tried to fix it, causing yet more damage with each attempt.

Sight unseen, it's hard to pin down whether the fix is simple, or if it will cost more than the radio's value.

73

 

[OldTech03]

Well it wants you to have only one frequency maybe a good place to start since you need to start somewhere would be to check the VCO voltage at pin 7 of PLL pretty sure that is it from memory you may need to be sure and bring up a schematic at any rate there should be a test point again as I type I remember it being TP2 a resistor I think you should see something on the order of 1.4 volts on the lowest freq and about 4.5 on the highest frequency if that is happening then we can have a big sigh of relief because the will be doing its job. Yes you will still have a problem but not a VCO problem most likely well it's 1:30 in the morning I should not even be trying this snoooooooozzzzzzzzzz.. I'm gone.

 

[Alan Anderson]

I have a 3300HP that when you first powered up, frequency was fine, change channels (some channels not all) and the frequency would be completely bogus - and actually drift. I ordered a PLL chip just in case, turns out changed IC6 & 7, problem solved. Don't know which one was causing the problem but almost exactly the same symptom as above and IC6/7 corrected the problem. Glad you figured it out in the past. Must be a common problem on these radios.