cb repair in Dublin

billy the cb

Is there anyone fixing cb radios in Dublin, I have a superstar 3900 that needs tuning up and maybe a repair. I have tried shops in Dublin that sell them but they do not repair and they say they don't know anyone they can recommend which seems strange

watty

Normal.

You need someone very skilled, highly educated and years of experience. A repair bill could be as much as a new one if Insurance, PRSI, Rent, Electric, Depreciation of very expensive test gear and wage commensurate with a long professional training/Education.

Unless someone has fiddled with innards they never need "tuned up". What's the problem with it?

billy the cb

watty wrote: »

Normal.

You need someone very skilled, highly educated and years of experience. A repair bill could be as much as a new one if Insurance, PRSI, Rent, Electric, Depreciation of very expensive test gear and wage commensurate with a long professional training/Education.

Unless someone has fiddled with innards they never need "tuned up". What's the problem with it?

Thanks Watty am and fm don't seem to modulate but ssb seems ok , only just got this superstar 3900 given to me, I have only tested it on a scanner but fancy sticking up a antenna, any help would be appreciated.

watty

Unless you run it into a 50 Ohm "dummy load" or the scanner is next door, you'll overload the scanner.

jmcc

The other thing to bear in mind is the age of the rig. If it is an old one (early days of CB in Ireland), then it might be cheaper to just buy a new one.

Regards...jmcc

billy the cb

As I said it seems to work on ssb, tried listening to it at a distance with the scanner, get a signal ok on fm and am but no modulation. Would hate to throw it out if it is something simple. by the way thanks jmcc and watty for your comments .

jmcc

billy the cb wrote: »

As I said it seems to work on ssb, tried listening to it at a distance with the scanner, get a signal ok on fm and am but no modulation. Would hate to throw it out if it is something simple. by the way thanks jmcc and watty for your comments .

It very much depends on the distance. A few metres away will overload the scanner, as Watty pointed out. You might need to test it from about 100 metres or so depending on the antenna setup. The point about the age of the rig has to do with the way that components age. The obvious components that would have age related failure would be the power transistors (heat stress) and the electrolytic capacitors. However this would take place over years of usage.

Regards...jmcc

billy the cb

Opened it up to have a look for wires out or lose connections, got exited when I saw a few connectors not attached, but i think they are for testing.
I need to test it on am and fm some how or get it to someone who knows what the are doing , no dxing for me yet

watty

Don't adjust ANYTHING!

jmcc

One possible way to test for AM would be to key the mike and then whistle. The modulation/signal meter on the front panel should move or fluctuate when you whistle into the mike. It is a very crude way of checking if there is any AM modulation happening.

The other thing about that image is that it looks like the rig might have been modified in the past. Look at the switch that changes between AM/FM/SSB and see if there is any damage or disconnected wires.

Regards...jmcc

billy the cb

jmcc wrote: »

One possible way to test for AM would be to key the mike and then whistle. The modulation/signal meter on the front panel should move or fluctuate when you whistle into the mike. It is a very crude way of checking if there is any AM modulation happening.

The other thing about that image is that it looks like the rig might have been modified in the past. Look at the switch that changes between AM/FM/SSB and see if there is any damage or disconnected wires.

Regards...jmcc

No movement on am or fm but moving on ssb when I whistle, looked last night for lose wires but couldn't see anything will have a good check tonight, thanks jmcc

billy the cb

watty wrote: »

Don't adjust ANYTHING!

No just took the top of looking for wire outs , not going to twiddle, cheers watty

watty

FM works by varying the VCO and putting the carrier full power, so if SSB works all the RF is working and only one connection missing.

AM works by using an audio amp to vary the voltage on the RF PA, with carrier applied, sometimes the amp used to drive the speaker on receive.



So AM and FM missing needs an expert engineer or technician. It suggests the rig has been "got at" and/or twiddled.

I do have information on an SS3900 (there are maybe 4 or 5 version). Expert test gear is needed too.

No CBs are very good, and the cost of repair vs new ones is high. Other than adding Mosfet instead of bipolar PA and frequency counter/Display little has changed on them in 25 years.

billy the cb

watty wrote: »

FM works by varying the VCO and putting the carrier full power, so if SSB works all the RF is working and only one connection missing.

AM works by using an audio amp to vary the voltage on the RF PA, with carrier applied, sometimes the amp used to drive the speaker on receive.



So AM and FM missing needs an expert engineer or technician. It suggests the rig has been "got at" and/or twiddled.

I do have information on an SS3900 (there are maybe 4 or 5 version). Expert test gear is needed too.

No CBs are very good, and the cost of repair vs new ones is high. Other than adding Mosfet instead of bipolar PA and frequency counter/Display little has changed on them in 25 years.

Thanks watty for your time, I am no expert but do have a rudimentary understanding of electronics, I can see from the meter (if that is ok) that it it punches the deck on am and fm but no movement on talking or whistling, on ssb meter dose not move unless you talk or whistle then only half way. unless l hook a watt meter up to it that I can trust I cant tell the power output, receive seems ok as I can hear the boys from Europe on 27.555 no problem with the springer antenna l got with it on a biscuit tin in the sitting room. Any how half wave silver stick arrived today hopefully I get it up over the weekend and swr it with the built in meter!!! and have ago on ssb if that is all that works that will do me as I have no interest in local contacts, propagation is my thing ( fascinates me ) still I would like it checked out by a expert, hence my question cb repair shops/ ham shops, once again thanks for your help.:):)

billy the cb

Well I got to test the 3900 today and it works got a contact, me in Marino and contact at the airport on ssb. Asked him to check am for me and he said he could hear me so it must be working. But the way the needle acts is still baffling me ie full key up on am but no movement when you speak, Still back to the same question is there anyone in Dublin who is a rig doctor that can check it out?

watty

AM there is 1/4 of the carrier of FM.
On AM you may only see the needle move a little and on FM not at all.

Often people turn up the power on AM (on preset) and then it distorts badly. The RF MUST be at 1/2 volts (= 1/4 power) or else it can NOT be fully modulated.

The FM though is at the power of the loudest SSB whistle always at all levels of microphone. Turning up the FM drive simply interferes on adjacent channels without increasing power at all.

AM is of no real interest or Value here. Originally it was the only mode allowed in US. The UK allowed FM but not AM or SSB when it was first legalised.

SSB is best for DX and FM is for "very local" and much better range than AM. FM is good for "mobile" as no "clarifier" adjustment is needed.

sensormatic

is it just the case of the rig being set in swr mode/?

billy the cb

Well I wish I hadn't go the bloody thing (superstar 3900), got a silver stick half wave up today and having a job swring it. Its grand down at 26 but at 27.555 it is 2.2 have to take it down and shorten it tomorrow. Sill don't know if the superstar is working properly!!!

carbon nanotube

billy the cb wrote: »

Opened it up to have a look for wires out or lose connections, got exited when I saw a few connectors not attached, but i think they are for testing.
I need to test it on am and fm some how or get it to someone who knows what the are doing , no dxing for me yet

nice to see an old skool electronic circuit board.:D

watty

Only SSB is good really for DX.
AM is obsolete since 1950s and FM is for local / Mobile

Molloys Clondalkin

agreed am is very obsolete unless your a russian taxi dispatcher or of the religious variety

billy the cb

well you boffins explain ssb to me in a way I can understand

watty

Read
http://en.wikipedia.org/wiki/Single-sideband_modulation

and then come back and ask questions.

SSB is harder to tune and needs more electronics. But compared to AM uses 1/2 the Bandwidth (50% more range or less power consumption) and has no carrier (x2 to x4 range or less power consumption).

A 4W PEP SSB rig can only do 1W AM without distortion.

billy the cb

watty wrote: »

Read
http://en.wikipedia.org/wiki/Single-sideband_modulation

and then come back and ask questions.

SSB is harder to tune and needs more electronics. But compared to AM uses 1/2 the Bandwidth (50% more range or less power consumption) and has no carrier (x2 to x4 range or less power consumption).

A 4W PEP SSB rig can only do 1W AM without distortion.

Cheers watty:o

billy the cb

Well here it is so far on my adventure with the 11m band, old rig acquired not sure how well it works!! Swr come atu acquired , half wave antenna bought, rig seems to work. Talked to a few locals told I am slightly of frequency. Now waiting for my first dx.

watty

The inner smaller knob beside channel sets frequency as does the larger outer. One may only affect RX and the other RX & TX. Using a frequency meter (do not connect it direct to rig!) or someone local believed to be accurate you can find what slight adjustment and put a pencil or CD pen mark on the faceplate for each knob. The coarse adjustment is either +/- 5kHz or maybe 10KHz so you can even tune some of the "missing" channels. The 40 channel switch on each band A to F only mostly goes in 10KHz steps, some are 20KHz I think

Most of the bands that rig does are actually illegal to transmit on. Only one set of 40 channels on the A to F switch are legal in Ireland to transmit. It does the Irish Public Address band and the UK FM band too.

I have one of those I modified to Amateur Radio 10m (nearly it does 28 to 29.4 instead of upto 29.7) to do 10m and also SSB on 2m and 70cm (144MHz and 430MHz via old Microwave Modules boxes).

For Dx it's a pretty poor set really, for decent performance and DX you need an Amateur licence and for do-everything 100W mobile and base a Yaesu FT857D or FT897D. You'll get DX 100x more often as you'll be able to operate in bands from 1.8MHz to 440MHz with over 200x power allowed on CB. (25x on the rigs mentioned)

http://www.yaesu.com/indexVS.cfm?cmd=DisplayProducts&ProdCatID=102&encProdID=8CBB7C4BDBAF40129AD4253A4987523C/

I've not used my SS3900 at all since I got an FT101ZD and a Yaesu FT817ND.

billy the cb

watty wrote: »

The inner smaller knob beside channel sets frequency as does the larger outer. One may only affect RX and the other RX & TX. Using a frequency meter (do not connect it direct to rig!) or someone local believed to be accurate you can find what slight adjustment and put a pencil or CD pen mark on the faceplate for each knob. The coarse adjustment is either +/- 5kHz or maybe 10KHz so you can even tune some of the "missing" channels. The 40 channel switch on each band A to F only mostly goes in 10KHz steps, some are 20KHz I think

Most of the bands that rig does are actually illegal to transmit on. Only one set of 40 channels on the A to F switch are legal in Ireland to transmit. It does the Irish Public Address band and the UK FM band too.

I have one of those I modified to Amateur Radio 10m (nearly it does 28 to 29.4 instead of upto 29.7) to do 10m and also SSB on 2m and 70cm (144MHz and 430MHz via old Microwave Modules boxes).

For Dx it's a pretty poor set really, for decent performance and DX you need an Amateur licence and for do-everything 100W mobile and base a Yaesu FT857D or FT897D. You'll get DX 100x more often as you'll be able to operate in bands from 1.8MHz to 440MHz with over 200x power allowed on CB. (25x on the rigs mentioned)

http://www.yaesu.com/indexVS.cfm?cmd=DisplayProducts&ProdCatID=102&encProdID=8CBB7C4BDBAF40129AD4253A4987523C/

I've not used my SS3900 at all since I got an FT101ZD and a Yaesu FT817ND.

Thanks for your comments, looked at the rigs you suggested they are some bit of kit, would love one of those baby's. but of coarse we all have to start some where, I got the SWR come atu to see how I was doing as I did not trust the rigs meters, just as well as the Swr seemed incorrect. Maybe Watty you could answer this question when I use the atu on ssb the watt meter reading on the unit dramatically reduces but seems fine on am and fm. Big learning curve for me all this rf malarkey but thanks to people like you and the tinternet I have learned a lot in the last few weeks.

watty

You need to whistle. There should be ZERO power on SSB without audio.

Also to measure SWR you need to calibrate the forward to the "set" line and then read SWR on Reverse.

Only use AM to measure SWR as SWR is the SAME on all modes and AM uses the lowest power. If there is a power setting (I think not on these), then you set to low power.

On a 100W rig I might use 1W AM to measure SWR.
On my 5W rig I use 100mW AM to measure the SWR.

Never use SSB mode to measure SWR and avoid CW/FM mode. Always measure SWR and "tune" aerial at lowest practical power (set needle at full sensitivity). Properly set up AM is 1/4 the power of FM. Peak SSB or CW anyway.

One... "tuning up" at full power can damage the rig if there is a bad mismatch. At 1/4 power (AM) that's almost impossible.
Two... "tuning up" at higher power blocks other users. It's rude.