RCI 2970

DJ · Post by DJ » Friday 30th Nov 2007, 16:56

Radio receives ok in AM far as I can tell but on ssb , the stronger the signal is the more distorted it is. If I crank the rf gain all the way down the strong signals come in clearly. Its so bad that I cant hardly understand a really strong signal. I just had a 2950 here and its receiver didnt do this. The buddy I got it from says that it has been like this from the begining.

Does anyone have a clue what it might be? perhaps a defective cap or voltage regulator? AM works fine, ssb receive VERY distorted on good signals.

any help is greatly appreciated

thanks
DJ

Rick · Post by **Rick** » Saturday 1st Dec 2007, 0:49

To help us help you please read this link
http://www.radiomods.co.nz/forum/viewtopic.php?t=312

There are two 2970 to my knowledge, that why its best to give us all info you can like Board Number ect.

It sounds like you have an AGC fault, check to see if the AGC is active in SSB, let us know what you find.

DJ · Post by DJ » Saturday 1st Dec 2007, 1:51

OK lets see here, its an RCI 2970
the board number is EPT295013Z
not sure what the pll is
this looks like a 2950 to me but with an amp added on inside.
I dont see the battery up front on this one like a 2950 I had so Im thinking this is the second series with no battery.

main problem is that on ssb mid to strong signals are distorted, turning the rf gain way way down clears it up. AM seems fine in rx and tx.

I have not done anything to it yet other than look for bad solder joints. This one dosnt look like anyone has been in it messing around too much.

Rick, how would I go about testing the AGC

Thanks
DJ

Radio Make.
Radio Model.
PCB number.
PLL number.
What doesn't work on the radio.
What does work on the radio.
What you have tried so far.

Rick · Post by **Rick** » Saturday 1st Dec 2007, 3:02

Check the voltage on pins 12, 13, and 14 of Op-Amp IC1 (NJM324D) in AM and SSB, let us know what you find.

You may find that Q13 is bad. I do remember repairing 2950 where Q13 was not fitted from new.

There was a mod to the AGC timing circuit, which is easy, just solder a 270K resistor across diode D9 (1N4148) it best to solder this on the copper side of the PCB.

As for testing the AGC you need very good moving coil meter forget the DVM it just to slow. Connect the meter positive to the cathode of D8 and the negative the ground one of the steel tuning cans will do, if the AGC is working, you will small meter movements the difference will only be about 0.1 to 0.8 vdc. Hope this helps, let us know how you get on.

DJ · Post by DJ » Saturday 1st Dec 2007, 4:00

IC1
pin 12 ssb .4.0 volt and am also .4.0
pin 13 ssb 7.2 am -.1
pin 14 ssb -.1 am is 6.56

thanks Rick

DJ

Rick · Post by **Rick** » Saturday 1st Dec 2007, 10:01

The voltages you have given are about right. What is the Serial No?

DJ · Post by DJ » Saturday 1st Dec 2007, 10:06

Rick I just edited my last post I think I measured the wrong pins
ser736640

from the solder side of the board, 12,13 and pin 14 are on the bottom right of the chip with the front of radio facing me. that sound right?

dj

Rick · Post by **Rick** » Saturday 1st Dec 2007, 10:52

Look at the chip from on top (components side) you will see a half moon cut out or a small hole at one end of the chip, look at the cut out or hole with it on your left hand side the lower left pin is pin 1 going a long the lower pins to the right is pin 7, moving up to the right hand corner is pin 8 and moving to the left is pin 14.

The voltages you gave me first time was about right, so you must check the right pins.

As from Serial No 741000 Ranger made changes to the AGC circuit (see blow).

To speed up the AGC you need to changes the following components

Change R46 from 47K to 39K
Change R48 from 680K to 820K
Change R51 from 220K to 270K
Change R52 from 1K to 680R
Change R53 from 1K to 1K5
Change R58 from 4K7 to 3K9
In addition, solder a 270K across D9

C39 and C40 maybe Tantalum bead type capacitor if so change them to standard electrolytic radial of 10 volt, if you can get small 16 volt ones use them.

DJ · Post by DJ » Saturday 1st Dec 2007, 11:08

so are you saying the early 2970's like mine all had the symptoms I mentioned? This thing you cant hardly understand a strong ssb signal ( like someone a mile away without lowering the rf gain. I dont have all those resistor values here but I can get them. Ill order them up

thanks, I appreciate your help here very much

DJ

Rick · Post by **Rick** » Saturday 1st Dec 2007, 11:20

All I can say is I have not come across the very early 2970 so I do not know what they sound like, but Ranger must have changed the AGC timing for a reason.

I have add a drawing of IC1 pin out.

DJ · Post by DJ » Saturday 1st Dec 2007, 11:38

Thanks Rick, I will change those resistors and report back here with my findings. May take several days to source them but you can bet Ill get them. if the local radio shack has them I will do it tomorrow.

Im not just being picky, this thing is unintelligible on ssb if the signal is strong ( and I dont mean like in the driveway strong) a few resistors are a cheap enough thing to try.

thanks again

DJ
edit: RS only had 2 or 3 of the resistors so Im ordering them from mouser, probably take 5 days or so to get.

DJ · Post by DJ » Friday 7th Dec 2007, 16:43

Update:
,Rick
I replaced all the resistors and both caps you suggested and it is still the same. I have not replaced Q13 yet but I have a replacement and will try that tomorrow, is there any good pictures out there that show the copper side of the board with the components labeled?

Could a bad Q13 cause the severe receive overload on ssb but not on AM?

DJ

Rick · Post by **Rick** » Saturday 8th Dec 2007, 9:30

Has the mod made any difference? If the answer is no then it looks like the AGC is not working, Q13 is switched on when you switch to SSB mode, which speeds up the AGC. It looks like you need to monitor the AGC line for this you will need very good moving coil meter to do the test. If you have a meter. Connect the meter positive to the cathode of D8 and the negative the ground one of the steel tuning cans will do, if the AGC is working, you will small meter movements the difference will only be about 0.1 to 0.8 vdc. Hope this helps, let us know how you get on.

DJ · Post by DJ » Saturday 8th Dec 2007, 10:12

Rick it goes from .7 to 3.0 volts when I transmit on a radio close by. I have not done anything with q13 yet, is that the culprit?
that is measured with a fluke 76 digital meter with bargraph display I dont have a decent analog meter
thanks
doug

DJ · Post by DJ » Saturday 8th Dec 2007, 10:50

I just replaced Q13 with a nte289a npn transistor and voltage at d8 cathode are still .7 to 3 volts or slightly higher

with no signal, switching from AM to LSB or USB it is .7 on ssb and about .18 on am

Rick · Post by **Rick** » Sunday 9th Dec 2007, 2:47

Check front end diodes D21 and D22 (1N4148) also check D18 and D20 (MC301), see what the voltage is at the anode and cathode, the problem is you may load the circuit when on the cathode of D18 with a DVM, I would you a scope to do this test. Can you also check Pin 14 of IC1 in SSB and AM with a strong in put signal leave the RF gain control at full gain.

It difficult to sort out an AGC fault with out the right test equipment.
but there is one think you can do and that is to clamp the AGC using an external voltage, you will need a PSU which can be adjusted from 0 to 5 volts, if you have a PSU like this then unsolder the anode end of D8 and apply the test voltage to the anode of D8 varying the voltage on in coming signal you should see if the AGC control line is working. Let us know how you get on.

While D8 is out of circuit, DO NOT TRANSMIT, as this will probably blow up the front end.

DJ · Post by DJ » Monday 10th Dec 2007, 11:09

OK, I replaced D21 and D22 just because I had some 4148 diodes and it may have helped just a little bit but not much.

with a dvm on D21 and D22 I get ZERO VOLTAGE on either end of both diodes. I have an Oscilloscope and on D18 cathode I get from 0 to 1.4 with a strong signal and .1 to 2.0 on the anode

on D20 its .8 to .9 cathode and .1 to 1.3 at the anode all readings are no signal then high signal ( is there a comon replacement for D20 and 22?, is it some kind of pin diode?

I do have a adjustable power supply and it seams to vary the output of pin
14 on ic1 on ssb it goes from .6 at zero volt to 6.0 volt and on am it goes from .9 to 6 volt

from .5 to 3 volt with a strong signal when d8 is installed normally.

I think I got that right but if something looks fishey to you let me know and I will retest.

thanks man

doug

Rick · Post by **Rick** » Tuesday 11th Dec 2007, 4:34

Your Quote
with a dvm on D21 and D22 I get ZERO VOLTAGE on either end of both diodes. I have an Oscilloscope and on D18 cathode I get from 0 to 1.4 with a strong signal and .1 to 2.0 on the anode

I think you are loading the AGC line. Your scope probe needs to be 10:1.

on D20 its .8 to .9 cathode and .1 to 1.3 at the anode all readings are no signal then high signal ( is there a comon replacement for D20 and 22?, is it some kind of pin diode?

Yes D20 and D22 are very fast switching diodes. I have seen them fail but it is not common

End Your Quote

Setup the test like so unsolder anode end of D8 so it is isolated from Pin 14 of IC1. Next connect the positive from your adjustable power supply (PSU) to the anode of D8 and connect negative to ground one of the steel tuning cans will do.

With your adjust PSU set at zero on the anode of D8.
Switch to SSB and find a stronger signal it should be very distorted.
Now increase the PSU voltage (Do not adjust the voltage more than 6.5 vdc if you do you may destroy various components in the front end) and you should get decrease distortion to the point where the received signal is ok. Let us know how you get on.

Before you replace any components, you should check the component is faulty, it not a good idea just to replace them this can be very misleading, for someone that is trying to help.

DJ · Post by DJ » Tuesday 11th Dec 2007, 11:08

OK this is with the scope probe on 10x
D21 and 22 at anode AND cathode both read the same, about .1 volt at low signal and maybe a little over .1 with a strong signal

on D18 cathode its 0 volt then 2volt with strong signal The anode goes from .1 up to 2.5volt with high signal

D20 cathode reads 1.0 volt at low signal and 1.2 with strong signal the anode goes from 0 to 2.0 volt

Now I remove D8 cathode and hooked the + lead to it and ground to a can and had a buddy that is close enough to make it distort and at 0 volt he is distorted and if I turn the voltage up to 5 or so volts he gets clear for a second or two then it gets bad again. if I lower the voltage then run it back up it does the same thing ( gets clear then goes bad after a sec or 2 )

So it has some effect but something kicks in and overides it somehow.

make any sense?

THANKS FOR YOUR PATIENTS
DJ

Rick · Post by **Rick** » Tuesday 11th Dec 2007, 11:50

Ok voltage at D21 and 22 is ok.

Next unsolder the anode of D16.

Connect the positive from your adjustable power supply (PSU) to the anode of D16 and connect negative to ground one of the steel tuning cans will do.

With your adjust PSU set at zero on the anode of D16.
Switch to SSB and find a stronger signal it should be very distorted.
Now increase the PSU voltage Keep the voltage as low as poss (Do not adjust the voltage more than 5 vdc if you do you may destroy various components in the front end) and you should get decrease distortion to the point where the received signal is ok. Let us know how you get on.

DJ · Post by DJ » Tuesday 11th Dec 2007, 12:53

OK, I did that and it does clear them up when the voltage gets up near 4 or so volts .

dj

Rick · Post by **Rick** » Tuesday 11th Dec 2007, 21:42

So is working ok then with the test applied to D16? I ask as I do not quit understand your last answer.

If is working ok then re-solder all back in place.
Then you need to isolate from Pin 14 of IC1 from the rest of the circuit.

Setup the test like so your adjust PSU set at zero, and connect the positive to the solder pad where you have isolated pin 14 (and not pin 14) or the anode of D8 and or D16 and connect negative to ground one of the steel tuning cans will do.

Switch to SSB and find a stronger signal it should be very distorted.
Now increase the PSU voltage (Do not adjust the voltage more than 6.5 vdc if you do you may destroy various components in the front end) and you should get decrease distortion to the point where the received signal is ok.

Also let us know what the voltage is at Pin14 with it isolated from the rest circuit and with a strong signal on SSB. Let us know how you get on.

DJ · Post by DJ » Wednesday 12th Dec 2007, 9:52

Yes it was working with the test applied to D16

OK I have isolated pin 14 (lifted it out) and by applying voltage to the anode of D16 like you said and it does clear up the distorted ssb signal as the voltage is increased.

with ZERO volts applied to D16 the voltage at pin 14 is 6.9 with or without a strong signal

but with about 1.5 v it reads zero at low signal and 6.9 at high signal levels

at about 3.5v and higher pin 14 reads 0 at low signal and 0 at high signal levels but strong ssb signals are nice and clear. a REALLY strong signal might require 5volts.

does that make sense?

tnx
dj

Rick · Post by **Rick** » Wednesday 12th Dec 2007, 12:11

You need to apply the test voltage to the solder pad where you have isolated IC1 pin 14 from, and not D16. It begin to look like the fault is with IC1 or components around IC1.

DJ · Post by DJ » Wednesday 12th Dec 2007, 13:27

Whoops, Ok I just did it at the pin14 solder pad ( pin 14 removed)
with no or very low signal its and 0 volts applied it reads 6.9v at pin 14 but as soon as any voltage past .1 or .2 it goes to zero at pin 14 with no signal

with a strong signal pin 14 goes to well over 5 volts and even 7 if I key another radio up here.

and like before when voltage is applied to that pin14 pad, it clears up the ssb audio a ton

I have an extra LM324 quad op amp here, is that the same as ic1? it says 324D on the original ic1 chip

thanks
DJ

Rick · Post by **Rick** » Wednesday 12th Dec 2007, 21:50

Yes the LM324 is the same chip. I would solder in a 14 pin DIP socket this will make it easy to fault find.

DJ · Post by DJ » Thursday 13th Dec 2007, 12:35

I installed a socket and the new chip, still works the same, distorted on high signal strength.darn it

Rick · Post by **Rick** » Friday 14th Dec 2007, 0:08

Unsoldering one end of R318 and see if this resolves the problem with a strong signal and can you give me the voltage reading once again from IC1 Pins 5, 6, 7, 12, 13, and 14 on AM and SSB with strong signal and same with no signal.

DO NOT TRANSMIT, While R318 is out of circuit.

It would appear that they is one or two problems, one is the AGC is being loaded or there is a bad component around the IC1. I think we are getting very close to finding the fault.

DJ · Post by DJ » Friday 14th Dec 2007, 13:00

Rick it still distorts with r318 one leg up. here are the voltages

pin 5 .1 low 5 volt high
pin6 .11 low 4.1 high
pin7 .2 low 4.7 high

pin12 .28 low 8.8 high
pin13 .28 low 3.1 high
pin 14 .63low 5.6 high

dj

Rick · Post by **Rick** » Saturday 15th Dec 2007, 0:21

The voltage you have given me for (IC1) are they for AM or SSB?
As I ask you for them in AM and SSB and assume that low means no signal and high means with strong signal.

Put R318 back in circuit.

Isolate IC1 pin 14 from the rest of the circuit.

Setup the test like before, adjust PSU set at zero, and connect the positive to the solder pad where you have isolated pin 14 (and not pin 14) and connect negative to ground one of the steel tuning cans will do.

Switch to SSB and find a stronger signal it should be distorted, and can you do the same test on AM. Now increase the PSU voltage to the point where the distortion just stops and let me know what the voltage is and check the current, it should be under 80ma. At this point it is important to let me know the current being used.

Do not adjust the voltage more than 6.5 vdc if you do you may destroy various components in the front end.

DJ · Post by DJ » Saturday 15th Dec 2007, 1:55

Rick, that was the ssb voltages in the last post I forgot to post the am, here they are and yes low= no or not much signal and high is a very strong signal
here are the am voltages and Im working on the rest right now

pin 5 .2 low 5.0 high
pin6 .23 4.2
pin7 .6 2.4

pin12 .35 10 volt yes 10 volts
pin13 .33 3.9
pin14 .7 2.1

more to follow
need coffee

Rick · Post by **Rick** » Saturday 15th Dec 2007, 2:21

I do not understand your voltages.

Your Quote
pin 5 .2 low 5.0 high
pin6 .23 4.2
pin7 .6 2.4

pin12 .35 10 volt yes 10 volts
pin13 .33 3.9
pin14 .7 2.1
End Quote

The easy way to write it is like so
Pin 5 low 0.2 high 5.0 AM
and so no.

Can we start again with SSB and AM or we will be here every, and I will lose the will to live.

Can you do the test in my last post.

DJ · Post by DJ » Saturday 15th Dec 2007, 2:49

sorry , not enough space between readings let me space them out more

heres the SSB voltages

pin 5 .1 low -- 5 volt high
pin6 .11 low -- 4.1 high
pin7 .2 low -- 4.7 high

pin12 .28 low -- 8.8 high
pin13 .28 low -- 3.1 high
pin 14 .63low -- 5.6 high

Here are the AM voltages

pin 5 .2 low -- 5.0 high
pin6 .23 low -- 4.2high
pin7 .6 low -- 2.4high

pin12 .35low -- 10 volt yes 10 volts high
pin13 .33low -- 3.9 high
pin14 .7 low -- 2.1 high

On the last test with pin 14 isolated and variable ps on ic1 pad 14
it takes about 4.5 volts to clear up a strong ssb signal

current on AM is 2.8ma with low signal and 3.0 ma high
on ssb it is 2.1ma low and 3.7ma with high signal

all voltage checks done with Fluke dvm

Rick · Post by **Rick** » Saturday 29th Dec 2007, 10:30

Change
C53 33p to 4n7
C56 10n to 4n7
R72 3K9 to 6K8
R73 1K to 2K2

Remove
D19 FC54C
R74 100K
R80 100R and replace with link
R318 100R and replace with link

You need to unsolder one end of R34, the end which was connect to R318 which is now a link, insert a 1N4148 diode with the Cathode connect to R34 and the Anode back to the R318 link.

This should make the AGC 90% better. I am still working on this and will get back to you hopefully later next week.

DJ · Post by DJ » Saturday 29th Dec 2007, 12:30

what does the n stand for in the capacitor rating
for example would a 4n7 be a 47pf cap in the US ?

thanks Ill dig up the parts and try that.
DJ

Change
C53 33p to 4n7
C56 10n to 4n7
R72 3K9 to 6K8
R73 1K to 2K2

Rick · Post by **Rick** » Saturday 29th Dec 2007, 23:37

Modern capacitor values are indicated as the following
Cap values (p) is used to denote (pF) picofarads
Cap values (n) is used to denote (nF) nanofarads
Cap values (u) is used to denote (uF) microfarads

1000p = 1nF
1n = 1000pF

1000nF = 1uF
1u = 1000nF

So 4n7 = 0.0047u or 4700p cap marked as 472

Modern resistors values are indicated as the following
Resistor value (R) is used to denote ohms
Resistor value (K) is used to denote kilo ohms
Resistor value (M) is used to denote mega ohms

2R2 = 2.2 ohm
3K9 = 3.9 kilo ohm
3M2 = 3.2 mega ohm

Period or full stop is replaced with alphabetical letter; this is to make it easier to read schematic diagrams.

Hope this helps.

DJ · Post by DJ » Sunday 30th Dec 2007, 5:32

my r72 is 6k8 from the factory , You didnt by chance mean for me to replace the 6k8 with a 3k9 did you? just though Id ask to be sure.
R73 was 1k so I will put a 2k2 in there if I can find one today.

=========
Change
C53 33p to 4n7
C56 10n to 4n7
R72 3K9 to 6K8
R73 1K to 2K2

Remove
D19 FC54C
R74 100K
R80 100R and replace with link
R318 100R and replace with link

Doug

Rick · Post by **Rick** » Sunday 30th Dec 2007, 7:49

Ok leave R72 as is. On the radio I work on it 3K9 and was change to 6K8.

DJ · Post by DJ » Monday 31st Dec 2007, 4:58

OK I did the mods. my radio didnt have D19 installed . I tried it last night and I would say it has improved some but still nowhere near as good as the 2950 i had here recently. the fairly strong ssb signals are still distorted but maybe not as much. The really strong signals are still bad. When I had the power supply installed so I could feed the agc manually that would totally clear up any strong signal by putting 4 or 5 volts to pin 14's pad. I didnt get to sxtensivly test it last night so I will use it some more to get a better idea of how its working.
I really appreciate the help Rick. I owe you some beers for your hard work

DJ

Rick · Post by **Rick** » Monday 31st Dec 2007, 6:41

D19 is SMD and is on the track side. See picture.
I am still working on a total fix and will get back to you.

DJ · Post by DJ » Monday 31st Dec 2007, 16:52

I found it , thanks.
that is one SMALL diode. heh!
Im also getting reports that it is a little distorted on xmit, maybe not warbling like i had thought. its hard to get a good reliable radio report here lately, Ill have to put my son on the mike and listen to him from the moble.
I have a couple mics to try on it now.
I think receive sensitivity is down a little bit with this latest mod

Rick · Post by **Rick** » Monday 7th Jan 2008, 7:38

I have been very busy, sorry.
I have last track of what you have done so can you check you have the right components installed,

R44 = 100K
R45 = 82K
R46 = 39K
R47 = 220K
R51 = 270K
R52 = 680R
R53 = 1K5
R72 = 6K8
R73 = 2K2
R318 = 100R Remove and replace with link
R327 = 10K Remove and replace with link
Solder 270K across D9
C52 18p
C55 Remove and replace with link
D21 and D22 Remove

As for warbling TX audio, how many amps is the PSU?

Can you check the voltage around Q38 in RX and TX?

On my test gear I have just under 85db range on SSB which is ok for a CB radio.

DJ · Post by DJ » Tuesday 8th Jan 2008, 3:14

Ill check that stuff tonight, I know I did not have D21 and D22 removed but I do now. I was wanting to check the driver and final bias current but I cant seem to find test point 7,8 and 9 . I see tp 1 2 and 3 with the big plate type jumper used.

My ps is an astron 35

Thanks

Dj

Rick · Post by **Rick** » Tuesday 8th Jan 2008, 8:02

The test points are TP3 which is common, TP1 which is for driver and TP2 which is for the final. Set the driver for 60ma with VR11.
Check the final for 140 to 170ma there is on way to reset this, do not adjust VC3 as this is part the harmonic trap.
On the PA board there is a pre-set for the PA bias but I can not remember the current setting, it maybe some where on the net.

DJ · Post by DJ » Wednesday 9th Jan 2008, 16:37

I did a quick look tonight and I need to do the following,
r52 is 6k8 change to 680
r327 remove and jump
change c52 to a 18p ( cant remember what it is right now but Ill dbl check it
c55 remove and jump

it may be a few days before I have time to mess with it again, I will let you know how it goes

Dj

DJ · Post by DJ » Saturday 16th Feb 2008, 17:14

Rick, I have been taking a break from this radio, it is ticking me off. Ill get back with it soon. Im starting to think it has other problems in addition to the agc. Ill get back on it soon.

just taking a sanity break

Doug

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RCI 2970

RCI 2970

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