I think those two SMD resistors are there for inrush current. Thing is they won't have much elbow room in the way of how much they could handle...SMD's as they are.
I'm going to guess that while handling this out of the box, you took precautions to avoid static discharge, especially when initially connecting up power to that PA board? IE..making sure there was no residual voltage on those power leads before connecting them, making sure no static charge was present on your bench or yourself.
1 watt resistors would work better for inrush current protection than those SMD's..considering the MOSFET type it has and the operating voltage and current involved.
Bottom line to it all though..is the response time from them should have been a lot better!
I have to agree with Sotiris, it is a questionable design around that MOSFET, particularly the B+ feeding. Tiny SMD's inline with a primary B+ feed where an amp or more will be present is hardly a robust way to design the thing! If it were me, I would have used 1 watt resistors and added a reverse polarity diode across that B+ input and included fusing, which would have protected those resistors instead of burning them up like that.
Well good luck with it if you intend to replace the blown parts. Me...I would be on the air with something else.
Gotta love them LPB's! Built like tanks!
Peace
K-ROCKS RadioOne
ZeroPointRadio
AM Stereo 1670
FM Stereo 92.1
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?
Hi RFB How it goes with the ASMAX? You still working your back-up unit with it? Best regards Sotiris
Yes. It's still working perfectly and sounding as good as the first day it was fired up. I have actually added another for a total of two LPB's with ASMAX exciters and two LPB's using the C-CUFF C-QUAM exciters.
Peace!
K-ROCKS RadioOne
ZeroPointRadio
AM Stereo 1670
FM Stereo 92.1
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?
Have you checked the +5VDC tab which is next to the temperature sensing tab on the exciter for the presence of +5VDC? If no +5VDC is present at that tab, apply +5VDC there, and apply +12VDC at the +12VDC tab and I bet that exciter will fire right up.
Peace!
K-ROCKS RadioOne
ZeroPointRadio
AM Stereo 1670
FM Stereo 92.1
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.
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.
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<=="
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<=="
Best 73, Carlos.
Yeah it's looking for the PA B+ sensing signal from the PA module. If the exciter's micro-controller was set up to rely on sensing that PA supply voltage in order to function then the PA module has to be plugged in and fed with the 28VDC supply voltage. The exciter will get it's 12VDC via the PA module and the ribbon cable, but your going to have to keep that +5VDC feed going to the +5VDC tab as well. You can use a positive 5 volt regulator and feed the regulator from the 12VDC tab on the exciter. Ground of the regulator connects to ground on the exciter. Output of the regulator to the +5VDC tab.
It would seem to me that it all needs to be connected together so the on-board sensing and diagnostics function and let the unit operate, or at least indicate something more on the display than those two items you mentioned.
Peace!
K-ROCKS RadioOne
ZeroPointRadio
AM Stereo 1670
FM Stereo 92.1
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.
Sad that you went through all that trouble and no response out of the vendor. Though things over in Greece are not exactly sunshine and birds chirping, I deal with another company in Greece that seems to have plenty of time and attention for it's customers. I get responses from them within a couple of days at most, sometimes within minutes of emailing them.
I'm sure the amp module can be repaired. It doesn't sound like too much is poofed on it. SMD parts can be a pain replacing. The MOSFET replacing will require having static protection to prevent damage to the new one. Just the slightest static discharge can damage them instantly. I doubt that MOSFET took damage from a static discharge while in circuit. My guess would be that either that MOSFET does not like operating at a lower voltage and killed itself upon applying the lower voltage, or it was bad prior to connecting voltage as pointed out by another member earlier.
If you get it repaired, might I suggest you put an inline fuse and holder on the B+ feed line inside your enclosure for that amp module. The design should have included fusing IMO. A pico fuse would fit nicely there and be far easier to replace than those silly SMD resistors! And I would replace those SMD resistors with good ol axial lead resistors.
If you don't find someone to repair it...contact me via private message and we can arrange something if you like.
Peace!
K-ROCKS RadioOne
ZeroPointRadio
AM Stereo 1670
FM Stereo 92.1
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.
Hi both of you. I was out of count ry the last 15 days, to a vacation trip, and just came back to office. OK. Carlos, FYI the SMT or TH components are acting exactly the same (and the SMT much better in most cases) when they are at a well designed circuitry. Only withdraw for SMT's is that most people lack experience to replace them in case of a failure. Otherwise its just the same component just shrinked in size! Now, about the 2 small burned SMTs, those are 0 (ZERO) Ohm resistors, as shown at a photo I have seen. They are SMT size 0805 and they should have just a "0" on top marked at them. However if those have been burned out, that is clearly a sign of MOSFET short circuit failure, that leads to an extreme overcurrent. Those 2 resistors then acted as fuses, and burned by the extreme current passing thru them! So at this time, you don't have DC voltage at the Drain pin of the MOSFET, and thats the reason there is no current draw from your amplifier. About the "exciter" board, I have no clue how it is supposed to worked, if it needs a feedback from the amplifier board to turn on the RF Out of it. I would try to find some info about it, although there aren't too much information available around, for them, not saying total lack of at least a basic schematic design... Seems that its a top secret of NASA or whoever else has done it... The good thing is that at least for now you have that board (PLL) showing some kind of life!
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.
