Stryker 497

[johnecashflo]

Hopefully I can get a little help from a pro on the problem with this Stryker 497 I’m working on.
Symptom.
No Deadkey or Modulation
Receive working flawless.
What I’ve found
All tx voltage working all tx transistor voltage check good. Found RF signal stops at L-40 no RF signal past L-40 so I checked for RF at tr914. No RF at tr 914. Removed and checked it tested good. After removing tr914 the RF signal started flowing into tr46 and through too RF input on power board. Now with RF signal flowing into input of power board the DK returned but with no modulation. Checked the regulators. They tested good. Did the old Elmer test and shorted two pins on regulator. Bam she went full power. Okay I now now the drivers and 2290 are good. So next I started tracking the modulation(1kz) injected at mic jack tracked it down to tr32 nothing past that point so for shits and giggles I removed it thinking it doesn’t matter if it is in or out for passing modulation. Well I was wrong. After removing tr32 I powered radio back on with signal injected thinking there’s no way that Tr32 would stop the audio signal after it tested good. I was wrong again full power she goes from 2 watt DK or 15 watt DK the radio is now working in all modes flawlessly (it seems) with tr -32 removed and tr914. I know it’s a bit long of a post but I was wondering if Someone would look at the 497 schematic and possibly explain why it’s working without tr914 and or where the problem may actually be that caused the problem to begin with. I’m not the best at reading schematics and I don’t want to start throwing parts at it. Thanks in advance for any advice.https://cbtricks.org/radios/stryker/sr_447_hpc/graphics/sr_447_sr_497_hpc_sch.pdf

 

[brandon7861]

I'll give it a try. When the RX rail is positive, TR32 shunts mic audio to ground (not the only function of TR32, but this is what counts right now) and TR914 shunts any RF to ground. It would seem that the RX rail is not turning off during TX, and my first guess would be the zener diode D76 being shorted. With that shorted, the base of TR37 is conducting and that holds TR36 in the ON state, and that forces both TR32 and TR914 to shunt their signals during TX.

 

[johnecashflo]

I'll give it a try. When the RX rail is positive, TR32 shunts mic audio to ground (not the only function of TR32, but this is what counts right now) and TR914 shunts any RF to ground. It would seem that the RX rail is not turning off during TX, and my first guess would be the zener diode D76 being shorted. With that shorted, the base of TR37 is conducting and that holds TR36 in the ON state, and that forces both TR32 and TR914 to shunt their signals during TX.

Thanks for the reply. This actually makes sense to me now as some of the voltages around the tr36-37-38 area weren’t really matching the voltage chart but I was thinking it was because tr914 was removed. Your explanation definitely makes sense now. I will check the diode you mentioned and I will let you know what the results are.

 

[brandon7861]

If the RX isn't turning off, "bam, full power" may have done damage to an active receive chain. By removing TR914, RF is allowed to be amplified while the RX chain is still active. Please tell me it didn't go deaf after trying that.