I did manage to find both MOSFETs as well as the 0 Ohm SMD resistors, so I'll start by replacing the damaged ones and then what happens.
Luckily, those 2 resistors aren't on a too much "crowded" area, but I wouldn't want to perform the desolder / solder operations myself as I lack the equipment for this sort of SMD stuff, so I'll look for somebody else to do it; if not, I have no other means but to try the "tradition" approach.
And what about for MF? I wonder whether many actually use "ununs" between the antenna, typically an inv. L type or a simple Vert.
As far as MF and inv. Ls are concerned, some just use an air core var. capac. between the lead in and the tx given the Z of this sort of Marconi which is in the vicinity of 50 Ohm. I mean, no coil, nothing, just the capacitor which IMHO may not work.
Others use a tuner w/o a coil, others a tuner+coil.
So, would a unbalanced to unbalanced xfrm be irrelevant?
Look forward to reading your comments. Thanks in advance.
In your detailed photo, it's the resistor right next to the + lead that really shows sign of damage - whereas the other one indicated the resistance I mentioned, but, of course, if you say both have that (same) value, then it was my measurement that was inaccurate. This 2nd resistor is surely damaged too as I said from the beginning although it doesn't entirely look so.
Let's see if I can find a pair and replace them, then it's the MOSFETs.
Thanks for explaining that abbreviation "mystery", but curiously or not, I decided to take a closer look at both resistors, and found out the 2nd one on the +28 V= tab indicates something like 97 kOHm on my dig. multimeter. I even mentioned this to RFBurns in a priv. message sent today.
And as I also told him, I feel there's no point in messsing more about his exciter and amp.. It's fine, very fine indeed, if, *only *I manage to get them checked and, hopefully, put into work, otherwise, I have no alternative but to leave them as they are.
Finally, you are right, the circuits seem to contain a "dirty little secret"; curiously (...), the only sheets with data on them don't bring any schematics, otherwise it would be a lot easier for the end user. As to having the PLL exciter display indicating something, yes, it does, after injecting +5V= on the respctive tab, but nothing else happens.
It must be exactly as you & RFBurns say, they work in tandem. However, as I said right in the beginning, a certain Danish member, Lisa, uses the same amp. together with a SSTRAN as I think to remember, so the amp. isn't just designed to work with other RFsource stuff. Probably too, her amp. doesn't even bring the ribbon cable or even the socket that receives such cable from this particular RFsource PLL exciter.
She reported both items work all right. Unfortunately, she hasn't replied to my message, so no more details about this.
Kage and RFBurns raise the money issue that allows stations to be on the air because they pay the licences and, if there's a technicality that should be corrected, then, well, this is indeed often ignored by those who get the licence money, i.e. the radio authority.
In my country for instance, there was a certain respected regional station, www.pef.pt, located in island of Madeira, that b/cast years on end with a 1 kW tx on 1017 using a "temprary" antenna, viz. an inv. L. At a certain timewhen I was a WRTH www.wrth.com collaborator, I decided to inquire why on earth that particular ch. was never included in the official lists: two replies came, one from the station saying "everything is in order", one from the radio authority saying that PEF channel was not listed because they, www.anacom.pt never issued a license for it. Again, that went on for years on end.
Other cases with several other stations here, both on mainland and in the Açores are different: the MW operation was halted for a number of reasons, either because the monopoles fell during a severe storm (fact) or because they continued on VHF-FM for their MF txs meant higher costs, particularly in terms of electricity.
The stipulated period for halting b/casts on a given, licensed fq does exist, those stations have them long overdue, but their fqs keep being listed. At this time, well, perhaps one of them actually lost or then gave off MF.
No fines, nothing, the licenses are being paid - and this, €€€€, is what really matters.
Exactly, SMD components, which have already became trivial in all things electronic, are to avoid. I have seen a few small MF txs on manufacturers' webpages that do show the inside, and they have no such silly components.
I think it was because of those, that I inadvertely caused a minor fault (static discharge perhaps) on a portable rx while changing IF filters for the VHF-FM band. Did the same on another portable and on a tuner, and everything went smoothly, no problem whatsoever.
Yes, things are not well in Greece, but that doesn't justify a lack of response; I believe that, being honest and eager to assist is nothing but a good recommendation for keeping a customer and winning new ones either via the previous one or directly.
I have in the meantime asked Sotiris / CQuam, who I suspect is the man behind the co. you mean, about what he meant by "are just for protection [fuse] and are *OR* in series."
Their 400 mW exciter for instance is one of examples that can be seen on the inside, and I believe there are no SMDs there.
As far as a repair is concerned, I am simply afraid of causing yet more damage in view of procedures against static, etc., so I'd leave it as is.
Having said that, yest, I shall prepare a priv. message via the forum, and will send it to you tomorrow.
To be frank, I supposed you'd say "it all needs to be connected together so the on-board sensing and diagnostics function and let the unit operate", so I feel it's pointless to connect that ribbon cable to the damaged amp. even if I don't apply any voltage to it, and hopefully, just hopefully expect the PLL exciter would indicate more than it did.
If my reasoning is correct, then you guess it, I'm stuck with two useless items that I could only hope might get properly fixed by someone with the knowledge & skill to do it.
One lesson from all this may be, that anything as sensitive and using feeble SMD components is perhaps not the best option.
The other lesson regards RFsource themselves - not to be recommended, otherwise they'd try to satisfy a customer.
Mind you that I have even suggested a guy I know who was here to contact RFsource because of a small VHF-FM tx, but they never bothered to reply either. As far as I'm concerned, using that band is a lot easier, particularly in terms of aerials, but 88-108 is simply not my cup of tea - I prefer MF for a number of reasons, one of which because I'm an MF DXer too.
After applying 5 V on that tab and connecting the 12 V= plug, the display immediately came to life (!)... but doesn't show anything else except "www.rfsource.gr" alternating with an indication saying "voltage alarm, VCC 25<=="
I is as you said, there's no current on the +5V tab, so I have already installed the +5V lead and soldered onto that tab.
I suppose the -5V goes to the left tab marked "temp" on the schematics - correct?
The schematics don't show, but the exciter came with a ribbon cable (soldered onto the PCB) to be connected to the amplifier. What I think is the -5V tab has one of the wires of that ribbon.
No, I never injected those 5 V=, but it puzzled me when I received the exciter, so I asked RFsource, and in a somewhat vague reply they said all I needed was 12 V=, so before I could make any silly mistake, I left the spot untouched.
But what you say does make sense, so I'll be doing it this evening, and then report back.
Meanwhile, I am using (don't laugh) this tiny valve iTx tx, and today I was amazed at the coveraged I got on a car radio.
This has been working with a somewhat crude ATU consisting of a 5 cm diam. coil with 100 turns of 0.5 mm copper wire, tapped every 10 turns, and (I know it should be the othe way round!) a tuner consisting of an old variable cap. (300 pF maybe, I don't know) and a 2nd another capac. of 1000 pF. The antenna is a 45 m inv. L with an 8 m lead. The coil was adjusted for max. signal on a rx, and I could notice a relevant improvement on the meter.
Now, this particular tuner and the external coil I am still to build is what I have in mind for the PLL exciter or any other.
"Well I guess the good news is that if there are less listeners, less radios, then there will be less stations on the air which will free up a lot of channel space." (Kage)
This is, on one hand, a very good thing just by itself, but is like paving the way for the disappearence of stations.
One other rather more technical aspect re. car radios is something I was haven't actually realised until paying a little more attention to what cars have already built in from the factory: the brand car rx that is "scattered" on the console, I mean, the display is one one place whereas the knobs are elsewhere, so quite unlike a good old, typical car radio.
Is it my plain ignorance or such car sets make the option for a car radio that the owner would like to choose & install almost or absolutely impossible?
Fortunately, there are still car radios on the market, but it seems certain old brands are currently with a zero or residual presence.
Another aspect: L&MW in the car radio. Despite many stations still using MW, and some LW, I suspect there's a heavy bunch of models around that no longer carry MW let alone LW.
Final aspect: the channel distribution on some car radio models. It simply makes me sick to see sets where one can't tune every 1 kHz, just 9 or, in the case of the Americas, 10 kHz.
Please excuse this belated post, but I have been away.
As I said more than once, the PLL exciter is not working either, and this is actually my main concern, so does it make sense to undertake the steps you both advise re. the amp., if the exciter is the way it is?
I fear not.
CQuam, would you mind, if I send you a priv. post via this forum?
You and Sotiris, I mean member "CQuam", have been very patient and helpul - thank you.
Yes, probably the 2nd MOSFET is the one you said, L7812CV, but, again, I can't tell for sure.
I think you included a photo, but nfortunately, it's not visible, just a square w/ a red X.
So, after having the amp. connected to the antenna PL socket of the metal box meant for both items, I apllied 12V=, and current reading was just 4.5 mA, and just a tiny bit higher the voltage (ZETAGI 1012-S pwr. supp. unit, regulated) was increased to its max. of 20 V=.
The RFsource owner was informed right from the beginning I would first use the same 12 V= for both the exciter & the amp. until I could use an idle 24 V= 6.67 A PSU for the amp. alone - and said it was all right; of course, less voltage into the amp. means less RF out, but it doesn't matter, I'm happy with the output level of the amp. working off less than the stipulated 28 V=:
" Yes the SDH203M [PLL exciter] board only needs 12V to power up! It can drive both PM62FDC and PM60F2 but it's designed to operate with the PM62FDC to enable all features (RF power measurement, temperature extra protections) If you don't need the full 60W PEP we can adjust the PM62FDC to operate At 12V for less RF output power (something like 20W PEP max or 5W carrier) And don't forget the output power is continuously adjusted by you from few mW to max (60W@28V or 20W@12V) I would like also to let you know that 28V/3A switching mode power supply Is available for 19.00 EUR " [09Jan'13].
Frankly, the main issue with both items is actually not the amp. for which I still need to know which components are damaged. The *main* issue is, as you certainly agree, the [more expensive] PLL exciter w/o which this or any other amp. is useless.
I am aware I risk having them just laying around & collecting dust, and that the "cure" so to speak may mean I should either look for something else that's more reliable or simply quit.
IRF640 (the one next to the [bigger] toroidal core);
L78IRCV () My eyesight doesn't allow me to clearly see the markings, and to complicate things, there are a few scratches or glue on the surface, that I can't erase; by the way, the central lead of this MOFET is unused.
If I could at least identify those 2 damages resistors, and replace them accordingly, then I could try to re-activate the amp., and then see what happens after properly connecting it to the exciter.
But tomorrow I shall connect the amp. and measure the current, and then report back to you.
(I know I should have built a dummy load, but I didn't, so in the absence of it, I'll use the antenna instead).
Very nice to hear from you. At first, I was puzzled when you mentioned our phone conversations, but then I read your name, and that was clear enough!
I partly understand your explanations, but please note the damaged SMD components aren't MOSFETs as they have only two leads, so, hopefully, they're simple components.
Also, I would leave the amp. aside for now, but, of course, can wire it to the PLL exciter again, and do the current measurements you advise.
What I would really need first is to get the PLL exciter to work, and I am sure it can work alone without the amp.
If you saw my photos, frankly, I can't think of what may be wrong.