Sidebar Sidebar
  • You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.

Cobra 89xlr

If you still seeing a change of voltage even though the voltage isn't correct; then chances are that VR is still working.

I'd check the caps.
BTW - how many volts out of the large filter cap?
 
I have the right voltage going into the voltage reg but not the right voltage coming out. What else could cause this even changing the voltage reg no difference?
 
I have 23.** volts at Emitter or TR201 also, the VR barely changes anything half a volt worth of adjustment (new caps on board) One of the diodes or a regulator must be out, as Robb said this power supply is fairly simple.

I am not going to power this radio off of 23 volts, I just got it to modulate properly after replacing several blown transistors and a total recap.
 
Ben Hebert said:
I have the right voltage going into the voltage reg but not the right voltage coming out. What else could cause this even changing the voltage reg no difference?
Click to expand...
A blown zener diode, I think.... But check for brown spots under r201.
D206 "WZ071" (Equivalent NTE138A) 7.5 v Zener @ 1watt
or
D205 "BZ162" (Equivalent NTE5075A) 16v Zener @ 1watt

I'm starting a list of materials to rebuild the power supply.

R201= 220 Ohm 1/2w
R202= 1.2k Ohm
R203= 820 Ohm
R204= 680 Ohm
R205= 820 Ohm
VR201 =
TR=2sc945/bc458
TR=
TR=
D205=BZ162
D206=WZ071
 
Last edited:
Robb said:
View attachment 20303Congrats, you traced thru the power supply. VR201/variable resistor on that same ac/dc power supply board will adjust the voltage output to the radio board. You will want to adjust VR201 with a voltmeter to read 13.8v. at the radio board. You can check the voltage output either on the emitter of transistor TR201; or where that wire goes to the radio board.

View attachment 20302
Click to expand...
Could I sub NTE152 (or TIP31C) for both parts at TR201 (C1061) & TR202 (C1419)
Stress is getting the better of me... sigh
 
Last edited:
Also test the large resistor on the regulator board to see if it is in spec - just for good measure. You can also upgrade the zeners to a 1 watt instead of the OEM 1/4w if you want to make it a bit more bulletproof.
 
I found the oem c1061 had failed, a tip31c fixed the issue also the 220 Ohm resistor was reading 30 kOhm, after replacement the power supply works good. Also the 1.2k ohm resistor had failed. (replaced also)
 
  • Like
Reactions: Robb

dxChat
Help Users
  • No one is chatting at the moment.


      Top Bottom
      Back