C91 as far as I can tell, will have to research it more when I get the radio back. Won't be the first time the board was marked different than the position.
-
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.
-
A Winner has been chosen for the 2026 July 4th Retevis RA89R Giveaway! Click Here to see who won!
Cobra 25LTD Classic
- Thread starter Smokinone
- Start date
When I recap, I usually follow the orientation of the old cap, I have seen too many incorrect silkscreen polarities. Sometimes I forget the orientation and reference the silk, but always write it down so if something acts wonky, I know which one to flip. Having a before pic is a lifesaver.
I found this Taiwan 25 like the one we're working on here. Kinda fuzzy as not a very good pic, but it seems to show that I have the new one in wrong..but fuzzy pic and fuzzy eye sight.
Yeah, hard to see the details, and I wish I had one here to look at, but I'd bet you a dollar it's backwards. I don't see many 25s these days.
It happens, age and eyesight be darned, I have perfect 20/20 vision and still
I looked at those and it seems the positive goes to ground, but not sure if the board actually has the positive position marked correctly. If the board is marked correctly, then it's installed correctly after my re-cap, if not, and that we're not sure of, then I installed it incorrectly. I need to get the radio back in my hands.
Thanks much guys for the research and good eyes.
edit: I seem to remember now that i think about it as it was the only 6.3 volt cap on the board.
That limiter circuit works on the negative going portion of modulation on that line and is what it senses for limiter action, that cap is tied to the base of a pnp transistor, so that's why the cap has positive side to ground, because the voltages going through there are negative with respect to ground.
Found a little better picture of a 25 with the same board ID. Appears I did put the cap in 180 out.
At least now you know what must be done. Fixing that oversight should take care of the spikes, let us know how it goes when you get back in it.
The stress of removing a small electrolytic makes it no longer reliable. We keep the popular value caps handy and just replace any that have to be removed.
73
Its not the stress of removing it that I was concerned with. When you apply reverse voltage, the cathode forms oxide and the anode oxide becomes damaged. It can lead to reduced capacitance, increased ESR, and sometimes shorts that make things interesting in circuits with more power than this one. Its just good practice.
But since it probably didn't get hammered in this particular application, maybe its fine.
Isn't this cap already kinda running reverse polarity as the positive lead is to ground? Or am I missing something.
I know reverse polarity can actually burst or explode an electrolytic cap, from experience, or lack thereof, I have had that happen to me.
I would imagine the voltage and current are very minimal as the original cap was a 6.3 volt cap, lowest value in a radio I have seen. The replacement was a 25V 105C, but I will definitely check it and replace it.
I know reverse polarity can actually burst or explode an electrolytic cap, from experience, or lack thereof, I have had that happen to me.
I would imagine the voltage and current are very minimal as the original cap was a 6.3 volt cap, lowest value in a radio I have seen. The replacement was a 25V 105C, but I will definitely check it and replace it.
- No one is chatting at the moment.
