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

The forum is very quiet these days yes, it certainly isn't anything like they way it was 10 years ago when it was busy.

I would just try replacing the diode with a new one and seeing if it works.

I don't have any info such as diagrams for them yet.

It is a 2SC2078, I do not know if RS stocks them.

It's good to see you are still around!

I dont have any info on that model myself, but it sounds more like a bad capacitor (or a few of them) in the audio path, effectively hi-passing the audio, cutting off the lower tones.

An incorrect SSB offset calibrations could also be possible, resulting in the frequencies being cut by the IF filter.

I suspect that it has overloaded the front end of the RX chain, most probably the shunt diodes, D1,D2,D19,D20.

Sounds like it needs to go to the tx from the mic, I would have to check it though

Mount the new MRF455 / SRF3775 on the rear panel on the bottom of the radio instead of the top, much more room there

It would pay to have a close look at the reset circuit which does a reset every time the radio is powered up, I have seen them fail to produce a sufficient reset pulse time, causing the MCU to not correctly reset. The MCU reset pin is 49, the circuit consists of Q316, Q317, IC314 and a dozen other m...

The only way to read the TX and RX freq on a radio is to hook into the offset oscillator, however, this will not give you the on channel frequency, as it would need to be mixed with another frequency (to match the radios IF), for instance if you hooked into the 148, you would be seeing a 34MHz frequ...

I have just used some very short hookup wires to the main PCB after mounting the 455 on the rear panel, worked fine, I think I did rogerbirds mod from memory.

This is a great post, thanks for sharing it.

I am always on the look out for parts radios, especially radios like the HR2510, Lincoln etc.

So if you have anything, please let me know what you have and what you want for it, international shipping may be feasible if it is a radio I particularly want to get for parts.

I found a mistake on the PCB layout, there are two r27 on it, one below q8 and one just to the right of it, one of those will probably be r37, see which one connects to d22/r569 and then q18

I got a bunch of used mcu from the guy that was doing the chip switch installations in the USA, you might be able to get some from him, you need to specify the exact mcu number you want, as there are a few variants.

If only I could remember who it is...

Am finally home (for today anyway!) had any more progress with this radio ?

Thanks for the diagram, that was slightly better ! the resistor to lift is R37, not 57.

Unfortunately the circuit diagram I have for that radio is rubbish, I cannot make out most of the part numbers etc. But the first couple of things I would do is try removing the AGC function in case that is staying turned on, this can be done by lifting R37, Q18 is the AGC control transistor. The RF...

Replace it, as it effects the serial communications with other device such as display and plls, I have also come across issues with the factory glue causing shorts to the traces underneath them, so it might pay to clean original glue off, and replace it.

Pull and clean every plug on the mpu pcb, also pull the display pcb and resolder it all. Especially the through holes as I have seen those fail killing the display and confusing the mpu. If you have another radio you can pull the display pcb from it helps, as that can eliminate that as the problem. ...

Sorry for the delay, I had been away, I cant process registrations until I get home to generate the serial number.

I emailed you your serial number a few minutes ago.

Can you please answer EACH of the questions I asked, I need to know the answers to all of them in order to be able to narrow down where the fault could be. On the back of the vol/on/off control there are two connections, usually a red wire and orange wire, you should have 13V on BOTH wires when the ...

Alignment info is on the site here: http://www.radiomods.co.nz/pc385align.html

Glad to hear you got it sorted out. An easy way of getting the existing MPU IC out is to actually cut all the pins off the IC, and then desolder and remove them one by one, I found that to be one of the simplest ways of getting a faulty one out, and also helps avoid damaging the PCB traces from exce...

Does the meter light up? Does the channel display light up? Has the inline fuse blown in its power cord? Have you checked for 13V at the on/off switch to confirm that power is getting to the radio itself ? Have you made sure it is not set to PA mode? You should be getting 5V at D19 with the radio tu...

I should drop in here more often by the looks ! I wish I wasn't so busy with other things, anyway. One thing to try, as weird as it will sound, is swap out the LCD PCB, I have seen instances where a faulty LCD PCB has caused the MPU to appear to be faulty, it is a long shot, but an easy thing to rul...

Hi,
there are 3 possible causes, listed in likelyhood of failure.

C33 (10uF 16V), TR35 (2SC945), IC4 (MB3756)

The forum handles images differently, if it is a very large image the forum will link to it instead of displaying it on the page. There is also a button shown under the image name after you have "added" it to "place inline", if you want to have it display on the page then you nee...

The large IC is not the PLL, it is an MPU, which controls TWO PLL's, along with many of the radios functions, such as the display etc. There are differences between the MPU programs, and this includes the functions of its pinouts. Personally I would just keep the 2510 working, electronically they ar...

I can do radio work via post if you cannot locate anyone down there that knows what they are doing, to be honest, I do not actually know of anyone else apart from me that works on AM/SSB CB's in NZ. As far as getting CB items in NZ, that can be hard, if I need anything I import it from the US or UK ...

HI,
Sorry, I know little about HAM equipment, all the ham information on the site is what I had collected from other sites and people over the years, I did not write those bits I'm afraid.

That sounds fine at that point.

Check the voltage drop across R111 (tell us the voltage on both sides of it, in TX and RX), I have come across issues on this and similar chassis where a capacitor is loading down the DC supply causing a large voltage drop across that resistor, it sounds similar.

What I have done is move the 10.24MHz xtal to the PLL, break the tripled 5.12MHz output, add a crystal for NZ and then modify the oscillator to allow it to work 4MHz higher for the new crystal. the tricky bit is that sometimes this can load the oscillator when on SSB and the clarifier is turned full...

I have converted AX144 for NZ channels before, it is a bit involved, but can be done by modifying the current circuitry's design and adding a few parts, realistically it can be tricky to get working properly sometimes, which can take a lot of time to convince it to work properly on all modes, as one...

I would suggest upgrading the Zener, you can use any 10V Zener, but I suggest you get a 5W version, which is less likely to fail again.

lbcomms posted whilst I was... Definitely worth checking the AVR to confirm it is operating correctly, I have replaced that circuit with a 7809 without any problems (I did add a 220uF 16V Electrolytic cap to it as well to ensure it had good smoothing, just a part I had a lot of, a smaller value woul...

I am trying to see how pin 6 can be fed with 11V, as it passes through the band switch and returns to the VCO via the VR1/VR2 trimmers, so I am suspecting that there may be a short on the band switch wiring. (unless my diagram is a bit dodgy and is not showing a connection, which I suspect may be th...

What are the voltages of all the pins on that IC (mid band ch 19).

There is a Zener diode on that PCB, marked on the diagram as MZ205 (next to C5), it would pay to check that it is OK.

I think that I only have one set of diagrams for a spartan, I do not know if it is the same as yours, as they do not have the PCB number marked, but it is for a uPD858 PLL, so it may be the same one. According to the diagram AM power is VR6, so if that matches up then it will likely be the right dia...

Thank you very much Sue, that will definitely come in handy !

If you are meaning the Nato 2000 FM then that information is on the website:
http://www.radiomods.co.nz/pcma001salign.html

Hi, What did you find to fix the display ? If there is no audio in all modes then it is something to do with the last signal or amp stages. If you have a RX signal with no audio then at a guess the squelch amp may be shorted out, check IC101 (NJM2902) on the main PCB slightly right of center towards...

The MPU PCB is a complex thing, without suitable test gear you stand no chance of locating the fault, at the very least you would need to determine what is working correctly on the PCB (if anything), you need to check the frequencies and control signals of the VCO's, and also the digital waveforms c...

Hi, the upload limit for a post is set to 5MB, so you may be able to post it in another message, would be helpful for people to see it here.

I believe (although I have never tried) that you cannot replace an MB8719 with a MC145106, as they have a different PD output, one is reversed from the other.

You can replace the MB8719 with an RCI8719-99, which can be obtained from various places online.

The Cybernet chassis (which the Jumbo is) is known for having poor AM power, I have come across many radios that could not do 4W on AM because of the audio problem, in reality your probably best to just set the AM power at 2.5-3W so that you have some swing on AM, if you need more power just drop a ...

Check TP1 first, if the voltage is at one extreme (close to 0V or 5V) all of the time then the PLL is trying to compensate for the frequency being incorrect, if the voltage is 0V the first thing you should do it try replacing C3, C4 and C5 (they smooth out the voltage feeding the VCO), if one has sh...

L20 is the 54MHz filter, it is tuned to limit RF output on 54MHz (1st harmonic), you need a spectrum analyser to adjust it properly.

Your probably best to just adjust it back to about 3/4 (towards the top), that should at least be approximately correct, certainly closer than where it is now.

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