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

Is the frequency noisy at pin 10 of IC2 ? (when using the injected 4V at TP2)

Are RA3 and D149 OK ?

Is R140 correct value ?

I feel it is time I had a go.. Check for frequency problems at Pin 2 of the PLL, if it is noisy or erratic then lift R121 and inject a stable 4.00V into TP2 (pin 5 of IC2) and monitor frequency at pin 2 of PLL, if problem persists then check C97, C98, TR29, TR28, if they are OK then replace IC2. If ...

I had increased the file size limit on the forum to 70MB, but obviously the server wouldn't allow it.

I will look into it.

A good way to avoid loading the circuit down if you are not connecting through a scope is to have a small value ceramic capacitor in series with the counter probe, something like 5-10pF is usually suitable. Also come more comments, L23(AM), L24 (USB)and L25 (LSB) are the 10.7MHz I.F. offsets, these ...

It would be best to sort out the internal wires, otherwise it could cause problems later in its lfe for people trying to wire mics for it. Lucky for you, once some time ago I made some notes... Pin - Function - Colour 1 - Audio - Pink 2 - Audio Earth - Coil Inductor 3 - RX - Green 4 - Earth - Black ...

Lets try this without a mic, to give us a definite cause, be it the radio or mic. Unplug the mic, now with a bit of wire or some other metal object short between pin 3 and pin 4, this should make the ext.+ int. connection earth properly, and would normally turn on the audio, HOWEVER, you had an issu...

I am 99% sure it should be TR43, not 45, I compared the diagram to one from a very similar chassis, and it was 43.. I will have to fix up the numbering!

C186 not C182

After having a second look at my diagram, it could be TR43 not TR45, the 3/5 is hard to read due to a mark.

The RX speaker feed comes via a different source than the PA speaker feed, that I why you need to confirm that the RX wire from the mic plug does indeed go to the external speaker socket. When in PA mode, the PA socket gets its earth directly from the PCB, but in CB mode the earth comes from the RX ...

OK, firstly I would check that the wire leading from pin 3 of the mic socket is heading to the rear of the radio and connects to the ext. speaker socket, to confirm that the RX wire is correct, as if that is incorrect it will kill RX audio. After that I would start by assuming that there is a compon...

have you tried an external speaker, to rule out a problem with the internal one.

I will look into this further shortly

Put it in the normal repairs category, you can try to upload the file, I do not know if it will work though.

No idea, I have never seen a HTX10, I have worked on a 485 though.

I found the above info after doing a quick search.

However, seeing as you want the HTX10 info, which is somewhat different, I found this... 1.open radio look up on front face board if you look very carefully you will see 2 solder pads where there could of been 2 pins for a jumper plug you will see one side goes to a smd and the other goes to a groun...

You should really try looking on the site first...

http://www.radiomods.co.nz/trc485mod.html

Well done on working out the problem! Rick, maybe we should keep on the same radio for these puzzles, that way we can cover a lot of the common faults that occur to it, then people could use it as a reference for repairing the HR2510/Lincoln radios. I have come across C60 being shorted myself before...

5KHz is in between channels, so although the main mod gives you more bands of channels, the 5KHz shift gives you an OFFSET that is between channels. a 5KHz shift is probably over kill, and I doubt you would use it, but over here in NZ (and probably Australia) it comes in handy, as the NZ band is 635...

ooh ooh I know !!

Pick me, pick me !

Come on guys, this is good one, and a great idea by Rick, so join in, see if you can work out what is wrong.

The guy doing those is actually a member of this forum, I do not think he has been around for a little while though.

It sounds more like the regulator may have failed, I think it was Q36, a 2SD device.

It could also be the big adjustable resistor that is mounted inside the chassis, I have known those to fails also.

I recommend that you state the PCB number, as there are a few different versions of the selector, depending upon the variation of the model it came from.

Glad to have been able to help, I have worked on a fair amount of the 2510's and Lincoln's, the VCO's failing is a common problem.

Here is the VCO section, in case you dont have it.

Do you have a circuit diagram there ? you will need it to work out where the caps are in relation to the other parts.

OK, with that now ruled out, the next thing is to look at the surface mount capacitors, as I have found bad ones before (usually the 100pf in series with the crystal, but I do not think that is the cause this time around). Check C379 (33pF) once I found this was faulty, this stopped the 100MHz VCO f...

You can probably replace it with a MRF455 instead,it will require different mounting, and some capacitor changes (as per the HR2510 / Lincoln mod), but I expect it would work, and I doubt the final would ever fail again.

HI David,
thanks for the offer, I do not need the part now though, as the person that diagnosed it, got it wrong, once I got the radio here I traced the fault back to a mixer not the PLL.

TP305 will be correct also, as the 38MHz VCO will be compensating for the incorrect frequency from the 100MHz VCO (as TP306 is correct). The main PLL checks for the correct frequency from the last mixer (IC304), and adjusts the frequency of the 38MHz VCO to suit, on 28.000 IC304's output should be 6...

Sorry, ignore TP301, it is a voltage test point for the 100MHz VCO, I misread my notes, you need a scope to see the voltage jumping around at that test point, which happens when the caps are failing. It sounds like the counter is not picking up the 38MHz signals very well. I do suspect though that t...

If you do not know which parts they are, just replace all of the Elect. Capacitors around IC306.

Also, from your description, it does sound like one of the VCO's is faulty, as one of them changes ONLY between <28MHz and >28MHz (the voltage stays the same below 28MHz, and jumps to a different voltage above 28MHz.

So from what I know so far, I would say C305 and C306 need replacing.

If you have a frequency counter and scope you can fault find which section is playing up, a common fault is drying out capacitors, which can cause one of the VCO's (the radio has two) to switch rapidly between two different frequencies, so the AVERAGE is correct ! Set radio to AM, 28.000 MHz, RIT de...

I would check L101, it could have burnt out the coil winding or shorted it.

Q104 would also be a suspect.

Personally I would replace IC101.

Has it always been this way or has it just suddenly changed ? The radio has two VR adjustments inside it, for the minimum and maximum power levels (to adjust what range the front panel control allows), off hand I can't remember the pot numbers, I seem to remember that they may even be marked as &quo...

Are you sure that is the correct PCB number, I do not have that one listed (although it could be an earlier version of something). If the circuit design is like the current models (most likely), I would try replacing C117, as it could be shorted, in which case it could be making the transistor turn ...

Personally I would use the full scale calibration, and then verify the scale reading afterwards at lower levels to ensure that it is OK

The forum only allows private messages to be initiated by people with a status of "technical helper" or higher, this was implemented to prevent spammers, and to also try and keep discussions within the forum, so everyone benefits from assistance, instead of just one person. If you are tryi...

A hole in the PLL is probably not a good sign... My suggestion it to set the radio on CH1 on EACH band and get the N codes, post them here, that will tell me if the EPROM is the problem or the PLL, as if the N code are shifting by the correct amount for each band, then it should indicate if the EPRO...

You can drop in another EPROM which has been programmed for the radio, as long as all of the band switch options have also been programmed into it, the raw data stored on the device is not "read" in the normal way, so you cant just go into it and see what it is doing, you have ton understa...

Divide the difference in frequency by 3, to give you the required frequency, as the 11MHz crystal is tripled before mixing in the the VCO.

So if you want 1 band up (or down), divide 450KHz by 3 to give you 150KHz, which is the difference in frequency from the original crystal and go from there.

It sounds like the balanced modulator has probably failed, that is where I would start. It could also be something wrong with FT3, as both SSB RX and TX pass through it. What I would do is start by trying to do an alignemnt and checking to see if any freqencies are missing, once they are all correct...

Glad I could help.

Tektronix have a very good name, I have a Tektronix scope myself, a 2432A, which is an old, but still very reliable unit.

I have not come across Lecroy before, but they seem OK too.. personally I would go with Tek.. purely because of the name.

If you have an audio probe I would suggest you connect it to the volume pot and see if audio is at that point.

Things to check:
C186
C72
Volume pot
TR19

At the top of all forum pages is a "search" link, you can use that to search for existing topics. Here is the thread I was thinking of: http://www.radiomods.co.nz/forum/viewtopic.php?t=2136 Also here is the modification page on the main site (this forum is only a small part of the site): h...

The mod is on the site, and it has already been mentioned in these forums, do a seach of the forum, and look at the site for the mod.

I would say try replacing the IC101 (NJM2909N) as that is the squelch amp and signal meter drive source (near the middle of the main circuit board), it is a fairly common part, so you should have no trouble finding one. I have only seen this part fail twice, one time gave symptoms like you are descr...

It depends on the version.

Look on the site, all the mods are there no point repeating myself here.

Heres the user manual.

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