The Defpom Forum, for RadioMods, S&M Software and Music by The Defpom

Rick

Remove the jumper PCB, this is at the back of the radio (A small vertical PCB that connects TP7, TP8, and TP9), then check the voltage at TP9 in USB or LSB Mode TX and you should have about 13.2 volts. In AM it should be only 5.60 volts, you can reset this by adjusting VR13 in AM Mod TX, so that the...

Rick

If the display is flashing ''codE'' then it is in the Test Mode, to stop the test press M1 and hold it for 5 seconds. If the display is flashing Random Codes then it is most likely that the CPU is faulty. If the display is flashing “codE 1 to 5” then the VCO or Mixer has a fault. If the display is f...

Rick

Looks like the finals have gone south.

Rick

Any osciliscope that will do 30 MHz plus will do not job.
I have Tektronix scope for sale (UK only) I am open to offers.

Rick

Remove the jumper PCB, this is at the back of the radio (A small vertical PCB that connects TP7, TP8, and TP9), then check the voltage at TP9 in AM Mode TX.

Rick

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.

Rick

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.

Rick

It is not a good idea just to change components without test them first as this can make fault finding harder.

Have you realigned the RX strip?

Rick

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 ...

Rick

Check D12, D13, D14, D15, and D16, D12 and D13 are a special type of diodes and must be MC301, all the other diodes can be replaced with 1N4148. The radio may have AGC fault, just try unsoldering one end of D68 and check to see if the RX is any better, DO NOT TX WITH D68 OUT OF CIRCUIT. You could al...

Rick

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 an...

Rick

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

Rick

If you need more swing than the radio will do from stock. Then you will most likely need to do some sort of swing modification, as it not something we do hear in the UK. You will need to do a search on the forum or do a search on Google and if you do not find what you are look for, then put a new po...

Rick

For a beam to be efficient, it needs to be about a wavelength away for ground, but this is not always easy to accomplish but any lower than 3/4 a wavelength is a waste of time.

Rick

Try replacing TR51, the transistor bolted to the side of the radio near the power socket right hand side.

Rick

There are a few thinks that can cause bad TX audio on this radio. You need to test the PA is working ok before do any more. If the PA is ok, then check the following caps C306, C314, C316, C318, and C322. Now ever if the PA is low then check the following caps C204, C205, C207, C209, C210, C211, C21...

Rick

The Cobra 148 GTL-DX is not the same as a 148 GTL, they are to total different radios.

I think you would be better off starting a new post, and when you post in is always best to put some info in the Post Subject line, as this make it easy to keep up with the Post.

Rick

You need to get it setup at a workshop that has a Spectrum Analyzer.

Tune any PA stage, should always be done with the Spectrum Analyzer.
There all too many people, which just tune in to a power meter with a dummy load and this look very impressive, but all you are doing is fooling you self.

Rick

You do not say which ones of the S9 it is, but if its the first one with MOSFETs PA stage then check out caps C158, C166, C165, C211, and C417.

Rick

Dave,
You can get the cap from Digi-Key http://uk.digikey.com.
Check D10 known ot go leaky and ZD2.
Not a nice PSU to work on.

Rick

You do not say if you DX33 is the HML or the HP model.
Check the choke on the back of the mike socket, it maybe O/C.

Rick

Look at SIL chips with the chip ID front of you the pin number go from lift to right.
The Audio and Voltage reg in you radio are of the type SIL that stands for Single In Line.

For more information check out
http://en.wikibooks.org/wiki/Practical_ ... le/Pinouts

Rick

Was TR51 low DC gain?

Rick

You should never adjust L38 as in is the 54 MHz trap. It may look like you are getting more power but you are putting out more spurious emission, which only lead to trouble.

Rick

Sorry I did not read all your first post.

Do you have any RX audio?
Is any of the LEDs in the bargraph working?
What is the voltage at transistor Q505, and Q506 in RX and TX?

Rick

The LS102 only has USB has it was made for 10 meters where USB was only sideband mode used up 1994, but most hams still use USB on 10 meters today.
The clue is in the model number LS102L.

Rick

Check the radio in the PA mode.

Rick

The right MOSFET to replace the RM3 is HUF75343P3. Amps using the RM3 have been around in the UK and Europe for over ten years now. The IRF520 will work but with lower power output and how it will last is any ones guess. You can find the datasheet at this URL http://www.datasheetcatalog.org/datashee...

Rick

To get the counter working you will need to do some voltage reading, you can get this info from the link I gave you in my last post.

I have had the frequency counter control board (EPT091V30A) fall in the past and a replacement is not cheap.

Rick

The DX95T2 is normally quit a nice radio, not my cup of tea. I have setup lots of them and only ever found a few faults from new. The push button switches, which are on the controls, Mic Gain, Dimmer, and Coarse and Fine shift, normally have a positive switching feel to them. The power cable (cord) ...

Rick

It must be very hard to do a search on this forum, as know one check it out and ask the same questions over and over.

www.radiomods.co.nz/forum/viewtopic.php?t=2243

Rick

Just go in any electronics specialist shop like Maplin and ask for 8.5 volt 500mW Zener diode, its that easy.

I wish I had a Gecol lol.

Rick

The Zener D11 is 8.5 volt at 500mW.
The radio is the same as a Academy, Elftone, and Fidelity 1000.
Nice radio lol.

Rick

The subject header dx99. Is not saying what the fault is.

The reason you are probably not get an answer is because you have not let the forum know, what you have try and what voltage reading of the fault circuitry.

If you what people to help you, you need to help them.

Rick

The smoothing caps are C194 and C195 (1000uf at 25 volt), I replace them with 2200uf at 25 volt. The fault lies somewhere around TR49 as the base voltage is to low in SSB, the components which control TR49 is a feedback circuit, which is formed by R240, R241, and D91. C190 is the AM audio roll off c...

Rick

If that is the case, then it looks like you are not turning the pass transistor fully on. If you can give the voltages base, collector and emitter of TR49, 50, 51, 52, 53, and 54 in SSB TX with full modulation. What is the R242 and R243 reading? Remember that the pass transistor is a PNP, hence it b...

Rick

No the pass transistor is TR51.

Rick

There is something wrong you say the Collector voltage of TR52 is 13.10, it needs to be 13.65 to 13.70, or the pass transistor will not turn fully on. Try this unsolder the pass transistor and solder a link from the emitter to the collector, now see if you have full power on SSB. CAUTION do not use ...

Rick

Thanks but I now have a front.

Rick

Maybe R243 has gone HR, check the voltage on the base, collector and emitter of TR52, the voltage in SSB should be base 7.75 vdc collector 13.65 vdc emitter 7.05 vdc.

Rick

An easy to check the NB is to use an hair dryer or electric drill, close the antenna socket and try tuning L10 for minimum noise, if you put your scope on the base of TR22 you should see the NB pulse, if not check the diode D3 it may test alright but may fall, also check C138 and C139. Most of the p...

Rick

What is the base voltage is SSB TX of TR51 with full modulation?
What is the collector voltage is SSB TX of TR51 with full modulation?
What is the voltage drop across TR51 in SSB TX with full modulation?

Rick

Have you ask the same question on CBTricks, as this forum is more world wide and that maybe why you are not getting a answer.

I could service or set your radio up for you but I am in the UK.

Rick

If you have a scope, check to see what is happing at the NB pulse amp and the NB shunt switch transistors, and check the coupling caps in and out of the NB circuit.

Rick

Most voltages are about 1 to 1.2 volts higher than they should be.
Check the regulator and RX/TX switching and let us know voltages you find.

Rick

Try a second radio before you go looking at the NB circuit, as maybe the vehicle or wiring causing the fault.

Rick

The AGC look a bit low on AM but this maybe just a Red herring. Set the radio to AM with the RF gain full CW and 20uV signal no modulation. Check the voltage on the following transistors TR13, 14, 15, 16, and 17? I know its a lot of work but its the only way to track down the fault. I assume you hav...

Rick

It would be best to let us have the PCB number.
What is the part numbers on the IC bolted to the chassis.
Without the above info it will be hard to help you as you can not read schematic.

Rick

I bought the radio with no audio Which audio RX or TX? out just a 1/2 watt dk in AM , SSB has audio but with low swing of 1 watt to 3 watt swing. After adjusting VR14 I was able to get back some swing on the AM, 1/2 watt swing to 1 1/2 watts. I have no RX . I have a Fluke 77 but no RF probes so vlo...

Rick

Any test above 50uV is pointless, as the AGC will load the front end, you are only trying to see if the AGC is working. Try the test in FM and SSB. Also check to see if there is any difference between USB and LSB, if there is try swapping out the SSB filter (FT5) as the AM signal goes through the fi...

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