CPI CP2000 issue can use help

[Crambone]

I have a CP2000 that RX is good till it gets warmed up the it drops back.
I thought possible bad electrolytic so I did a complete electrolytic replacement on entire radio but still same issue. The radio is 100% stock no mods.
I checked around with a FLIR and found transistor (17 marked on board 7H042) (2N5224) getting extremely hot around 300 deg F and all other components around 130 deg F that are on any of the boards. I took a pic of its location and placed a red dot on top.
I pulled the transistor and tested with a PEAK DCA 75 Pro and it shows what I Think is a good transistor.
Results: NPN
hFE = 139
IC = 5.00 mA
VBE = 0.756v
IB = 5.00mA
VCE sat = 0.095
IC = 5.00 mA
IB = 1.00mA
IC Leak = 0.000mA

I also took some vDC readings in both RX and TX
E = Ground
B = .4vDC RX & TX
C = 8.7vDC RX & 8.6vDC TX

Any suggestions on what may be causing this as I’m assuming that is what’s also causing my RX to go low when it’s HOT?

Thanks, Andrew

 

[nomadradio]

Can't tell where that transistor is on the schematic for the SMO board. And there's no parts-placement diagram to identify it that way.

If you had inserted an electrolytic backwards, it should get hot along with anything it might overload in the same circuit. Always worth considering when they all get replaced. If the new capacitors are all running cool, this probably isn't the fault.

Just not seein' it.

73

 

[Crambone]

Can't tell where that transistor is on the schematic for the SMO board. And there's no parts-placement diagram to identify it that way.

If you had inserted an electrolytic backwards, it should get hot along with anything it might overload in the same circuit. Always worth considering when they all get replaced. If the new capacitors are all running cool, this probably isn't the fault.

Just not seein' it.

73

Thanks, ya the first thing I checked against my pics, I took a Ron of pics prior to changing out the caps and everything is good. I’m going to change out the transistor maybe it shows good cold but has a thermal issue. If the new one heats up I’m expecting a resistor or cap going to ground must be shorted???

Andrew

 

[Crambone]

Ok I tracked it down to a 1K resistor that was shorted, changed out and nothings getting warm / hot & receive stays for hours.
New issue and I’m suspecting it was also caused by the shorted 1k resistor but I may be totally wrong. Channels 1-11 and 30-40 are all on frequency but remaining channels are off frequency
12 27.305. 21 27.415.
13 27.315. 22 27.425.
14 27.325. 23 27.455
15 27.335. 24 27.435
16 27.355. 25 27.445
17 27.365. 26 27.465
18 27.375. 27 27.475
19 27.385. 28 27.485
20 27.405. 29 27.495

Any help would be appreciated

 

[TM86]

Just a guess because I'm in a spot with no technical info. Sounds like one of the programmable divider inputs might be having an issue. You may need to build a truth chart from the working channels and then extrapolate to what the bits should be for the non working ones.

With that you can check the programmable divider inputs to see if what those chips are getting is correct. If not, start looking at what feeds those chips. If the inputs are good then you might have a bad IC.

Of course you'll have to test at every step to make sure you're on the right path, but as long as it's not the EPROM you can probably fix it.

 

[AudioShockwav]

I think the truth chart is in here:

Communications Power Inc. CP2000 Base Service Manual - CBTricks

May be of help

73
Jeff

 

[Crambone]

Ok I figured it out 3 electrolytic 10uf had gone high aver 12uf so I changed out all of them turned on and everything is back to normal.

 

[nomadradio]

Rock on! Just goes to show that the advice to change all the electrolytics really can save some aggravation.

73

 

[N8YX]

Rock on! Just goes to show that the advice to change all the electrolytics really can save some aggravation.

73

I have a couple CP2000s in my stash. One definitely is in need of recapping. They're both going to get it done as soon as my bench is back up and running.

Love that radio. My late friend Hank had one and I was very impressed with it when we had it on the air.