No receive and other issues on Cobra 29 NW ST

[JDE]

NPC is a brand - 9605 is the Date Code - you break down that number in groups.

First two are last two digits of the year it's made - in this case '96 or (19)96

The second group is the week of the year - 52 weeks in a year, 05 means 5th week.

The chip is a D2816 PLL or equivalent.

The radio still has a lot of the old OEM capacitors that can add issues to the mess you already have.

Since you're getting a RED TX light - it indicates something is working to even let the PLL turn that LED on - doesn't always do it but if the radios' PLL is healthy, the RX is not - tells me one or two caps the feed the power from the main Regulator that is over by the Audio chip - might be failed.

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You saw how C123 was, these caps are no different.

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Try looking for and replacing...C119 by Power Regulator (Above) and C114 by front panel PLL and C112 by PLL and TX side L19 - these work the main voltage Regulator that runs both the PLL and much of the Mic, TX and RX side for regulation and a clean power feed in key spots for the radio.

Time to get after those hot glue spots.

Awsome info, I'll get to that and grab some capacitors from digikey. Is a DMM a reliable way to determine if those caps are bad, or is that just a simple "yep, that cap aint a cap anymore" test?

For replacement caps, is there a certain process or info to use to make sure I'm ordering proper replacements? For example, C123 was 1000uf25v but the only other info on it was I think a temp rating(85c?), so I just searched for 1000uf 25v caps that had the same height/diamter/lead spacing as the one I was replacing and ordered what matched.

 

[Handy Andy]

There are some simple ways to check the caps to even see if they are viable...

In circuit - no power, put the DVM in Resistor 10X - and see if the cap will change the display - the DVM will supply a small trickle current to check the resistance across it's leads - Caps play screwy things with the DVM when caps are fine, they slowly lower the resistor reading one-way with the test leads while when reversed they do nothing.

When you have bad caps - the DVM sees a changing resistance all the time - because of the resistive effects the (formerly) polarized plates the cap once had, are now corroded and shorting together enough to show a resistive element in either way of testing polarity direction.

Another way is to buy a ESR ESL or ESC checker or see if you DMM has CAP mode right next to Diode Ω and anything else?

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[JDE]

There are some simple ways to check the caps to even see if they are viable...

In circuit - no power, put the DVM in Resistor 10X - and see if the cap will change the display - the DVM will supply a small trickle current to check the resistance across it's leads - Caps play screwy things with the DVM when caps are fine, they slowly lower the resistor reading one-way with the test leads while when reversed they do nothing.

When you have bad caps - the DVM sees a changing resistance all the time - because of the resistive effects the (formerly) polarized plates the cap once had, are now corroded and shorting together enough to show a resistive element in either way of testing polarity direction.

Another way is to buy a ESR ESL or ESC checker or see if you DMM has CAP mode right next to Diode Ω and anything else?

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I'm using a Klein MM600

Amazon product ASIN B018CLOSTC

 

[Handy Andy]

Then use it!

Read the manual...for their recommended process

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[JDE]

Then use it!

Read the manual...for their recommended process

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I've used that mode to test C123. That cap had let the smoke out more than once, has been leaking for X amount of time, and has a 1000uf rating. My meter showed it at around 750uf.

 

[Handy Andy]

For example, C123 was 1000uf25v but the only other info on it was I think a temp rating(85c?), so I just searched for 1000uf 25v caps that had the same height/diamter/lead spacing as the one I was replacing and ordered what matched.

That is how you pretty much have to do it, more along the issue of size and lead spacing for clearance and fit. Everything else might have to bargain/barter with to find values that are smaller to fit a larger outline than the ratings will allow - for example - a 1000uF 25V versus 50V the spacing in the can size goes UP in diameter for the height - else you can find height goes up and diameter stays the same but in a lower working value - but still should be higher than what you originally had.

In the time this radio and parts were used, they used MARGINAL voltage-ratings for working value parts - 10V versus a safer 16V or even 25/36V variety. This also places constraints on size and lead spacing.

You may find the lower working voltage of 16V might be the highest rating you can use, because the PERFORMANCE of the capacitor at that specific value was "calculated" for a lower working voltage so the FARAD / Charge to Coulomb / Joules working rates (the performance of the part) needed it to be that working voltage due to the ability of the capacitors own charge transfer character affects the performance of the circuit in question.