Help needed Air command superscope CB-640

[3pinplug]

Hi all
Just picked up one of these but it has a problem and was hoping some of you guys may be familiar with this radio, i am in the UK so we don’t see many of these.
The binary code is stuck on the ch9 code no matter what channel you select. The Vco appears unlocked as when i try to set the vco coltage via L216 i either have 5v or zero, also have no tx due to the vco issue.
Anyone familiar with these and can help?
Thanks
Mark

 

[unit_399]

Probably someone has messed around with the wiring on the channel 9 switch and it is stuck in the chan 9 position.

- 399

 

[Handy Andy]

+1 with @unit_399 on this - if the front panel has a CH9 switch - and it was pressed in while it was in storage - they oftentimes develop a memory where the plunger and it's carbon button - won't change state to open up and restore operation.

So look for and see if reheating the channel 9 switch solder contacts can make it recover.

The Channel 9 switch on many CB's was a set of diodes, but some PLL Chips had a direct Channel 9 pin that if shorted to ground, can be unsoldered but be aware of static or poorly done mods or if zapped with static, Channel 9 that's all you get - the PLL chip is toast and the ability to change channels went with it. (CMOS PLL types are notorious for this)

The PLL's with a set of diodes also used a separate pole of the switch that applied power to the front channel selector so it can change channels by logic state (Hi-Lo) that if left floating - the PLL ignores any input.

I hope this is a schematic to your problem child...

The Radio above uses a "Scan" function similar to a squelch - that keeps Channel 9 in a monitor mode so you can listen in and help others.

IT uses a jumper - I'll let you discover the rest.

 

[DoctorAudio]

All of the Superscope mobiles (CB-140, CB-340, CB-640) use the same PLL board. The board is double sided and has several feed-through eyelets that connect the top traces to the bottom traces. They are notorious for losing connection. 9 out of 10 times that one of these radios is having PLL/channel problems, one of the feed-through points is the culprit. Just re-soldering them won't always fix the problem as the hole design invites air bubbles when you try to flow fresh solder causing a continued bad connection. What I do (which I also do to double sided Royce boards that have feed-through problems) is to clean all of the feed-through holes out with solder braid then run a short length of solid wire through each eyelet hole before filling with fresh solder. This ensures a good connection.

 

[3pinplug]

Hi all,
Thank you for the information i will check out the ch9 switch and pass throughs and report back.