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Palomar 225 keeps blowing fuses when power leads are hooked up

Well you guys were right. I snipped the diode and hooked up power. No more fuses blowing.

However I think another issue arose.

I decided to do a test to see if the amp was any good. Meaning that it worked fully. So i hooked it up to my Cobra 25 and keyed up. Long story short I was told I sounded like I was talking morse code. On my power supply, it showed maybe a few amps being pulled but very fast, like back and forth between the 0 and the 2. Looking at the amp the pre amp light would come on when I keyed up. The middle light under the power selector would not light up at all. I didn't have the pre amp on though.

Now the Cobra 25 doesn't work right. First off it now pulls 6 amps of power just the radio alone, when it used to pull 1-2 amps. It pulls the 6 amps as soon as it's turned on.

It still transmits but now it sounds real weak. The receive on it sounds weak as well. it has the weather bands too, they still come in but not as strong as they used to. Also the TX/RX meter doesn't work anymore.

What is more I hooked up my SWR meter to the radio after the amp check and the SWR meter doesn't show any output or anything. The meter is ok, tried it on another radio and it works.

So it seems now the 25 has a weak receive, a weak transmit, no reading on my external SWR meter plus the inside smells of something burnt but I can't find anything burnt when I popped the cover.

No I did not hook up the amp backwards. I put the antenna feed line on "ANT" and the radio on the "XMIT" line.

That has me wondering if having snipped diode near the fuse holder inside the amp caused this to happen....
 
sounds like you did not have an antenna connected and now you have a dead output transistor in your cobra, I'm not saying that you did not have the antenna connected but maybe the key circuit is shot in the amp and the radio did not see an antenna.

open relay in the amp.
 
Sounds like a shorted final in the 25, clipping the diode has nothing to do with it but a junk amp does. Did you buy this under the assumption that it worked or just take a chance on it? Unsolder and lift the middle leg of your final and see if it stops drawing power, if so replace the final.
 
mackmobile43 said:
sounds like you did not have an antenna connected and now you have a dead output transistor in your cobra, I'm not saying that you did not have the antenna connected but maybe the key circuit is shot in the amp and the radio did not see an antenna.

open relay in the amp.
Click to expand...

So in other words you mean in the amp itself it didn't see the antenna? Also what's the key circuit you speak of in the amp? Is this an easy fix?

137 said:
Did you buy this under the assumption that it worked or just take a chance on it? Unsolder and lift the middle leg of your final and see if it stops drawing power, if so replace the final.
Click to expand...

I took a chance on the amp. However he threw in another amp at the last minute at no extra charge that he wasn't sure if it worked or not. When I went to test both amps, this one kept blowing fuses but the other one seemed to work ok.

I'll definitely try unsoldering the middle leg in the final and let you know the outcome. Hopefully that's all that's wrong with it and nothing else.
 
Robalo said:
Connect the black lead of your ohmmeter to the top tab and the red lead to the bottom lead. This is your collector base junction and it should read about 600 ohms. Now connect the black lead to the ground trace (emmiter) and the red lead to the bottom tab (base). This should also read about 600 ohms. It will be common to find open or shorted junctions. This indicates a blown transistor.


copied from the texas star amp repair website
Click to expand...

Something to watch out for: on many of the older analog VOMs, like the Simpson 260 series, the black lead is actually POSITIVE when using the resistance function. I put labels on all my multimeters, both analog and digital, indicating which lead is positive for resistance readings. Most (but not all) DMMs have the red lead positive for resistance.
 
137 said:
Unsolder and lift the middle leg of your final and see if it stops drawing power, if so replace the final.
Click to expand...

Thanks. I just did this. Sure enough the radio isn't drawing 6 amps anymore. Also the light on the TX/RX meter is bright again and it seems the RX sound has returned to where it once was, to include the weather channels.

So I guess my amp toasted the final. Wow.

I'm going to attempt to replace the final, the novice I am looking to learn.

Unless it's a bad idea, I think I want to replace the final with one that yields a higher wattage.

I know at one time the 1969 final was the "in" thing, but to my understanding they're now outdated and newer/better things have replaced them.

So....for a Cobra 25 WX that was built in October 1997, what final would you recommend?

And also is it a plug in play? Or must the radio be re tuned?

Again I thank you very much in advance. You all have been a big help.
 
Thank you for the link. I am also open to any finals that might be better than the 1969's.
 
Have a look at this, he is testing A
2SC2166
2SC1969
2SC2312
and His own replacement transistor
The Hfr-20W
Note these are all made by Eleflow
No tuning involved he is simply pluging the transistor into a improvised socket on the foil side of the radio.
A Very informative Video
watch
 
I bought some 69's from copper in a pinch, $15 a pop kinda sucks but I like'em.

Copper Electronics, Inc.

The other 1969 listing is for the copies, tried ordering those to just to try them out but they were out, $6 was worth a shot but I have not not tried ordering them again.

As for changing the final, easy as pie, hop down to radioshack and grab some thermal compound, its the white crap you'll see behind the final when you remove it, you'll need to put some on the new one. New one goes in just like the old one came out, make sure you put the isolation film and washer back. If you want my advice, don't tighten the screw all the way up before you solder the legs, just tighten it enought to seat the isolation washer, after you solder it then snug it down.
 
The other 1969 listing is for the copies
Click to expand...

If you are talking about Weazle66 in the links,They are Part Number HFR-20, they are made by Eleflow, and he is very clear about this.
They have a very good track record so far as being as good as, if not better than the original Mitsubishi 1969.

The problem with many others on E-Bay is they are marked "as" 2sc1969, and they are junk.
If you want an original Mitsubishi , Go to RF Parts in San Marcos Ca
RF Parts Company™ Amateur Radio Catalog
$12.95 each, Min order is $25

73
Jeff
 
mackmobile43 said:
sounds like you did not have an antenna connected and now you have a dead output transistor in your cobra, I'm not saying that you did not have the antenna connected but maybe the key circuit is shot in the amp and the radio did not see an antenna.

open relay in the amp.
Click to expand...

So you're saying you feel one of the relays is not working? How can I test this? I don't want to destroy anymore of my radios. But I do want to get this amp to work again.
 
Turbo T said:
So you're saying you feel one of the relays is not working? How can I test this? I don't want to destroy anymore of my radios. But I do want to get this amp to work again.
Click to expand...

If you have receive with the amp powered up then it's probably ok, you should hear the relay engage when keyed so find the coil side of the relay then you can ground it and see if it engages without applying rf power to it.

I don't have a pinout for your relay so you'll have to figure out where the 12 volt power source feeds the relay and the opposite terminal is usually the one you ground.
 

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