RCI-2990 No Receive

Warbird · Post by **Warbird** » Wednesday 8th Oct 2008, 12:58

I was given an RCI 2990 with an EPT295013Z board. When I got this thing it was a MESS. Physically the outside was in great shape, and the display worked... a good start. Inside wasn't so good. It looked like the previous owner had tried to hot rod it in every way possible. The most classic was the MRF-477 for the final transistor... which was blown... Oh I shouldn't leave out the fact that the amp board isn't original, it's a custom affair with 2879s. There were numerous diodes and resistors cut and hacked everwhere, a resistor had been replaced with a diode at R281... drove me NUTS until I found that one.

After putting things back to where they should be, replaced the 477 with a 1969 (didn't have any 2312s laying around), and rebuilding some traces, I got the transmit working. Yes, even the homegrown amp board works. The receive is the problem. I have checked through the voltages and everything looks good except the base and emitter voltages of Q18. I am getting B=3.18v, C=7.3v, E=3.96v. The base and emitter voltages are higher than the voltage chart from CBTricks says they should be. I have replaced Q18 with no change. I can inject a signal at D20 and get good response from the receiver, but the farther I get away from Q18, the less I hear of the signal. Once I get to the antenna connector, I don't hear much of it at all. All of the testing is done in AM because that is the only generator I have, I listened for carrier whine on SSB, but could only hear a bit on LSB.

I hope I have provided enough info that someone might be able to nudge me in the right direction, hopefully it's nothing to serious. If there's not enough info, please let me know and I can try to provide it.

Thanks all for your help.

Rick · Post by **Rick** » Wednesday 8th Oct 2008, 20:13

A few parts to check.
R76
R78
D20, D21, and D22
What is the voltage at each side of D18, D19, and D20?

Warbird · Post by **Warbird** » Thursday 9th Oct 2008, 12:42

Rick wrote:A few parts to check.
R76
R78
D20, D21, and D22
What is the voltage at each side of D18, D19, and D20?

Checked 'em out. R76 reads 1.4K, R78 reads 2.1K. D20, 21, 22 are all good, voltages D18 c=2.7v a=3.4v (I think I got those right, D18 is SMT on the back side) D19 c=1.6v a=.1 D20 c=2.0 a=2.7.

Thanks for the help!

Rick · Post by **Rick** » Thursday 9th Oct 2008, 20:36

I think you have D18 and D19 the wrong way round, D19 is normally on the trackside and is of the type SMD.

Try unsoldering one end of D18 and see if the RX comes back, DO NOT TX THE RADIO WITH D18 OUT OF CIRCUIT.

You have a lot of volts a round the front end, so a few thinks to check before we do any more, first check the voltage regulator IC15 and RX switching transistor Q37, then check the RF gain control is working you can do this by check the voltage at the junction of R75 and R76.

Let us know how you get on.

Warbird · Post by **Warbird** » Friday 10th Oct 2008, 11:40

Thanks Rick, you are right about me having d18 and 19 mixed up. The voltages are swapped for 18 and 19. D19 is c=2.7 a=3.4 and D18 c=1.6 a=.1... sorry about that.

Q37 is good on voltage, I will get back to you on R75 & 76 and IC15, although I am pretty sure IC15 and IC6 tested in spec.

Warbird · Post by **Warbird** » Saturday 11th Oct 2008, 11:59

Taking d18 out of circuit DOES seem to help, the static level is higher and reception from a nearby radio is louder, although I can't don't receive anything off of the antenna. The junction of R75/76 runs 3.6v with RFGain all of the way down to 0 all of the way up. IC15 shows 1-13.9 2-0v 3-8v.

Rick · Post by **Rick** » Saturday 11th Oct 2008, 20:13

When you post can you put the reference in the Subject line as it make it easy to track the post.

The IC15 and the RF gain are working OK.

I am taking in for granted that you have check the RX strip is aligned correctly.

It would be a good idea to check all the components between the antenna socket and Q18 as it sound like you have a weak signal at Q18.

Check all the diodes and caps, D18 and D20 are a special type of diodes and must be MC301, it maybe worth just replacing D21 and D22 has they can go leaky under load.

I have just noted that the voltage at D19 is wrong, I know this is SMD but can you unsolder one end and see if the RX comes back.

Warbird · Post by **Warbird** » Saturday 11th Oct 2008, 22:31

Sorry, I thought the subject naturally followed the thread. I'll try 21 and 22 and then recheck the voltages on 18, 19 and 20 since I screwed that up the first time and may have even confused myself. The radio is on frequency when in receive. I've done the PLL alignment (I don't have a scope though) and verified transmit and receive frequency by wiring in an FC390 frequency counter.

Rick · Post by **Rick** » Saturday 11th Oct 2008, 22:37

After think about the fault a bit more. I think you will find that L8 is open circuit, as you say there is 3.4 volts on the anode of D19, this should be zero volts.

Warbird · Post by **Warbird** » Sunday 12th Oct 2008, 11:09

Rick wrote:After think about the fault a bit more. I think you will find that L8 is open circuit, as you say there is 3.4 volts on the anode of D19, this should be zero volts.

I changed out d21 and 22, and rechecked the voltage on the others. Here is what I have d20 c=2 a=0 d18 c=2.7 a=3.4 d19 c=2v a=0. I DID replace L8 and was checking things from the antenna connector toward L8. It seems I get decent response when injecting a tone to the L8 side of C55, but REALLY weak on the L31/32 side of C55. I don't know how it is supposed to respond. I would think the signal should be about the same level until it gets amplified by Q18? I pulled C55 and it checks OK.

Rick · Post by **Rick** » Sunday 12th Oct 2008, 12:02

I do not understand, you say the Cathode of D18 is 2.7 volts but the Anode of D20 is zero volts, now can is be has the Cathode of D18 is connect to the Anode of D20.

What frequency is the tone you are injecting?

Recheck the voltage around Q18 and check for the mixer signal at Q19.

Warbird · Post by **Warbird** » Tuesday 14th Oct 2008, 12:29

Rick, I want to thank you for your help and patience, I think I am going to put the covers back on and set the whole mess aside for a while. I've been fooling with this one long enough and it has just worn me down. Besides, it is taking up too much space on the bench. One day, soon I hope, I will pull it back out have another go at it.

Thanks again!!

Warbird · Post by **Warbird** » Sunday 14th Dec 2008, 14:33

Rick, I just wanted to update this thread. Again, thanks for your help and patience. I decided it was time to dig into this thing again after reading a message on another forum. The symptom was the radio wouldn't go into receive mode which I felt was more my problem than not being able to hear. In the back of my mind I felt this radio would come out of transmit, but not engage the receive. Someone mentioned to check Q38. I checked mine and there was 7 volts on the collector. I changed it out and I had receive again. Although the S meter doesn't seem to be registering quite right, even after adjusting VR1 (quiet on SSB right now), but at least it has receive now. The recieve is very quiet, although it is hearing everything my Galaxy right next to it is hearing so things seems to be on track.

Like I said, I just wanted to update this and pass along the info.

Oops, looks like the message was on this forum... the one about the 2970 being stuck in transmit.

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