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RCI 2995DX CF troubleshooting help needed

Crambone

Well-Known Member
Jan 22, 2019
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Well while im waiting on parts I decided to look at my RCI2995 again. Im noticing on my friends he gets 4.5Vdc on TP7 that supplies 4.5Vdc to TP 8 and 9. Im only getting 2.4Vdc on mine?
My radio sounds like its keying, the fan speeds up the "ON AIR" & "TX" light up but I get NO POWER or MODULATION on all MODES but the PA works and sounds great.
Checked a few points for power
Q60 Collector (middle post) has 2.4V, Q62 has 2.4V Collector (middle post)
Q66 has Base 13.2Vdc RX and 13Vdc TX, Collector 2.3Vdc RX and 0Vdc TX, Emitter 13.7Vdc RX & TX
IC7 1)13.6Vdc, 2)6.45Vdc, 3)0, 4).85Vdc, 5)1.4Vdc (#5 speaker hums)
Q51 Base 13.6Vdc, Collector 8.8Vdc, Emitter 13.9Vdc
Test Strip:
AF I/P 0Vdc
AF O/P 0Vdc
GA 0Vdc
SQ 0-4Vdc
8V O/P 8.7Vdc
PTT 8.7Vdc
GND 0Vdc
MOD I/P 4.3Vdc
MOD O/P 4.6Vdc

TEST Points in Vdc: RX only
1) 0
2) ? Cant locate
3) 0
4) ? Cant locate
5) 8.1
6) 0
7, 8, 9) 2.4
10) 1.7
11) 2.3
12) 2.4
13) 0
14) 0
15) 2.3
16) 2.3
17) 0


Were does power for TP7 receive its power from?
 

TP7 gets power from the collector of Q60, one of the amplifiers (Q60-Q64) that amplify the exciter signal from the tx mixer, Look at your service manual and you will see the procedure for setting up TP7 (driver bias) for 10mA adjusted at VR13.
 
Ok I will look for a replacement thank you. I did have a question in ref to setting the bias. The manual states, “Set radio to 24.890 MHz, AM RX mode. Frequency setting at 29.699 MHz. Connect Multimeter to TP11.”
I’m assuming frequency setting 29.699 MHz is what you would set the Signal Gen at?
 
Ok I just checked the voltage on Q66 again just to make sure I had it correct and I did. I also looked at voltage on the 3 SM capacitors C265 is showing no voltage readings, C265 shows 13V towards C263 and 2v opposite, C255 shows 2.1v towards 263 and 0 opposite.
I also grabbed voltage off Q67 just to see. Looking at it from the top ishow 2v on the single top tab and on the bottom three left to right 13V. 2.3V. 13V
 
I just found a 2SB754Y in my parts bin I will install it tomorrow. What luck that was a buddy gave me a bunch on new parts he didn’t want anymore and 1 was in it!
 
So I pulled Q66 2SB754Y and replaced with new and still the same voltages? I tested the one Installed and the one I pulled and they tested good.
old new
hfe 184 144
Ube 536mv 547mv
Ic 6.3ma 6.4ma

I popped the collector pin off and Its showing 13Vdc but when installed it drops to 2.4Vdc Im thinking something shorted from the Collector to the TP7?
So I pulled the alignment board from TP7, 8 & 9 and tested continuity of each to ground. TP7 shows continuity but only for around 3 second then stops then shows again 3 seconds ..........! So it only does it under power if I unplug power it doesn't show continuity to ground? so plugged in switch on we have continuity as explained above. unplug with switch on no continuity, plugged in switch off no continuity. So only power and switch on will it show continuity?
Had a friend check his on the phone the same way and he doesn't receive any continuity to ground like I am seeing?
 
Last edited:
Ok. I just did some measurements on that transistor in AM mode. Here is what I got.

Base 13v RX 12.75v TX
Collector 4.3v RX 3.44v TX
Emitter 13.6v RX 13.61v TX
So I would look around in that area to see why you have zero volts on your Collector during TX.
 
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Had a friend check his on the phone the same way and he doesn't receive any continuity to ground like I am seeing?
There you go. Now you know the area to check and a problem to solve. Look at the schematic and figure out why. Your a couple of steps ahead of where you were yesterday. I measured the correct voltages in AM mode for you and you can use that to also help your troubleshooting. If you get stuck, post back. :)
 
sounds like you are on the right track.
Unit 75 already has you pointed in the right direction.

leave the collector of Q66 and the mirror board disconnected while you do your testing.

if you have a friend who has one of these exact models, then you can have him disconnect the same two components and ask him to measure the ohms to ground.
not just continuity, but an actual ohm value.

this will help you to know what "right" looks like as you test things.

most likely something along that line is either leaking to ground or shorted to ground, thereby pulling the voltage down.

start at one end of the trace on the schematic and work toward the other end.
never start in the middle.
this would mean that if you started at the Q66 collector end, your first suspect would be the collector of Q67, then R298, then C263, then C258, etc...
basically everything that parallels off that line. so, starting at the beginning, lift one end of each of those components, one at a time, and test the trace again.
look for the most drastic change and then test the part you removed.

now, how to interpret the results of your tests, well that's where the experience is handy.
I suspect that you will either find Q67 bad, or one of the caps that goes to ground, but that is just a guess.

good luck,
LC
 
Great thank you guys. I’m not sure how to lift an end on a surface mount component as most are?
 

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