Cobra 19Ultra stone dead receive help

[dss56]

Has anyone ever have 1 of these little cobra 19Ultra. It has no receive stone dead i put another radio next to it with dummy load and the 19ultra had nothing on the meter. It transmits and has good audio but no receive. Tried cb tricks it has some 19 schematics but no 19ultra.

Would anyone have a schematic for the pictured radio or info what might cause no receive?
thanks for any info

 

[Handy Andy]

Those three vertical riser cards - very carefully reflow some solder onto each pad. You have to remove that case and look on the foil side - or bottom side - and reflow the edge connections to the main board these little vertical cards have.

These "vertical board" radios turn into junk really fast - due to they can't handle vibration very well. The edge connector is soldered to the mainboard and with the newer lead-free solder - the connections made with the newer stuff are even more brittle.

This is an on-going problem with this technology, Cobra never truly learned to stop doing radios this way for it hurts their reliability as well as reputation for even having working equipment.

 

[dss56]

Hi Andy.

I did reflow the solder on all those boards. the one board that has the vco surrounded by a metal shield wall was reflowed and gave me transmit but still without receive. I did flex the complete board and still no receive thats why im looking for a schematic and voltage chart so i can do some further probing.

All the upright boards have surface mount parts and makes it quite hard to possibly fix this radio.

thanks bob

 

[Handy Andy]

To reflow and got TX is a good start, but there is a coil in that foil shield box they may have tweaked or has to be tweaked to make the VCO lock on both TX and RX.

One of the bad things about these vertical cards are their lack of true working value - once they develop a problem they are not easily corrected, adjusted or fixed. Pretty much a throw away, but more like salvage for parts you can use to build the next one that actually works and does not need the vertical cards.

They waste more time and effort going vertical than to simply have kept it condensed onto single board. They did get back to the older single layer design but not after several attempts to make these work.

I went to downloads.cobra.com and found some PDF's to help you - these pdfs' have the similar board you have and hope they help you.

Service manual one, covers the board you have - the schematic isn't the best in the other one but identifies how they put these vertical cards together to make these POS's work.

No guarantees...

 

[dss56]

Andy

Again you were on the correct track. I went and reflowed those up right boards and I was able to get the receive back. Those boards have surface mount parts on them. but the joints from the boards to the mother board i guess was the problem.
What was Cobra thinking doing this and the solder they used sucks seems more lead than tin and dull.

it was 1 of the boards towards the back left looking at the front of radio

Again I thank you for the tips and the help.

Bob in Boston

 

[Handy Andy]

No problem but once those traces begin to break, the radio simply becomes to delicate to operate.

As you can see in the service manual - the front panel is edge soldered and easily torn away from the mounting flange - so even the tug of a mic cord can wreck the radio.

The receiver gets signal from that rear riser card by antenna connector - that can also add to this as a "Dead receive" so the matching matrix it has, also contains the tap point to send the 1st IF a signal from the antenna for receive. If the receive goes dead, and you can't seem to figure out why, check there by the rear panel too.

 

[unit_399]

Good call, Andy.

- 399

 

[sunbulls]

Ditto the "good call" Andy! I found the vertical board that is attached to the two switches on the front the most problematic. In one case, I backwards engineered the switch board connections and hard wired the main board instead, thus eliminating the switch board entirely. Corrosive brown glue (time bomb) is another issue with the 19’s, especially on the print side around the PLL. The crystal is also held down with that junk. Even with its inherent problems I have a fondness for them as a monitor radio. Their squelch action is one of the best IMO, sensitive, yet smooth with no loud pop noise during the transition like so many other radios.