I am newcomer to this Forum which I was very pleased to find on the internet, and got even more pleased when I read a message from a Danish member, Lisa, who happens to use an amp. I recently bought from RFsource, Greece, together with her SSTRAM, mod. AMT3000, tx
That made drop her a line, and while I await her reply, maybe I can in the meantime ask you members a question precisely about RFsource envolving their “SDH203M”, a 400 mW PLL exciter, and the “PM62FDC Those should be a giant’s step as compared to the tiny “iTx” valve tx I am using for nearly a year.
In early March, after installing and wiring the exciter, there was no reaction after applying 12 V= as the display indicates nothing & the 2 control LEDs are off.The exciter does bring a ribbon cable with a socket meant for the amp. but I suppose the exciter should work alone as the amp. is merely an extra: in fact, it’s the amp. that needs an exciter!
After connecting the amp. to the exciter, I applied 12 V= to it, and... two of the SMD components (resistors?) to the left of the +/- 28 V/.3.3 A connection simply burned. I have no means to know their values and replace them.I explained Mr Theodoros Kotsalidis I could use 12V= for the both items or then 12V= for the exciter and managed 24 V= for the “pallet”, the amp.
Sadly, the leaflets coming with both items, exciter & amp., are meagre in details, and the circuit diagram don’t have component values, and on top of all this, RFsource doesn’t reply to my repeated mails, either because it’s no more working, which I very much doubt as several recent searches led me to www.facebook.com/RFsource
where we can see there are messages dated 9th April which is an indication they’re alive, or then simply because they simply don't care.
Does anyone has any experience with this PLL exciter?I will highly appreciate your help so that I can finally put the box into work.Thank you very much in advance.
I hope Lisa also replies so that I can get a tip on those two burned SMD components.
Applied 12vdc to the pallet amp and it fried a couple SMD parts? The pallet amp is designed to operate at 28vdc. And the exciter did nothing with the same 12vdc applied as well?
At this point I would suspect something is drastically wrong with your power supply, or connection to both units was in reverse polarity. If your power supply has a large current capacity, and things got connected in reverse polarity, that indeed will fry a few things.
Peace!
K-ROCKS RadioOne
ZeroPointRadio
AM Stereo 1670
FM Stereo 92.1
I'm glad, that there was finally one reply to my RFsource issue.
Thank you!
No, there was no polarity change. I connected the antenna first, left the modul. & RF controls as they were (fully counterclockwise, just as they were when I received the items), then applied 12V= to the exciter alone., i.e. w/o the amp. being connected at all, but the display & LEDs remained unlit. Needless to say the dispaly ribbon cable *was* connected to the exciter.
After that, I wired the amp. to the exc. & ant. socket, then applied 12 V=, and that's when those 2 SMD components right near the +/- solder contacts on the "pallet" got smoky... I think I was careful enough when connected the 12 V=. I would have already replaced the SMDs, if the diagram had any component details.
Apart from all that, I suppose, and expected, the seller would provide some assistance, or at least would reply to the new customer's question... I even sent them photos of it all so that they could examine everything, and then report back: surely, that wouldn't take them too much time, and would work in favor or their reputation.
In the absence of RFsource's reply, I'd be most pleased, if a member also using the "pallet" could help me identifying those bloody SMDs.
One last note: I was tipped about not feeling surprised, if the exciter doesn't work *if* the ribbon cable to control the amp./"pallet" is not connected to it - but it was when the SMDs "experienced" a sudden heat blow.
How long since informing them? I can understand if it's been more than a few days.
The online documentation would suggest that the units can operate individually without the other, so you should have seen that display indicate something as well as the LED's.
Appears to me that if operating both as a single unit, your B+ to feed the whole works goes to the amp board's 28vdc+ input, and exciter power comes from CN1 Pin 1 on the amplifier board and would go to the exciter's 28/12 vdc input.
CN1 Pin 3 would go to the exciter's PA Voltage measurement connection, CN1 Pin 2 to a ground on the exciter, CN1 Pin 4 to exciter Temp, CN1 Pin 5 to exciter Forward, CN1 Pin 6 to exciter Reflected. Also note a +5 volt connection point right next to the Temp connection point on the exciter. (may need to put +5vdc there)
Can you post or link up to those photos of the units? Would help in analyzing whats up.
K-ROCKS RadioOne
ZeroPointRadio
AM Stereo 1670
FM Stereo 92.1
The first e-mail to RFsource was on 8th March, so quite a long time ago. As I said, if one can find April posts at their Facebook page, then Mr Thedoros Kotsalidis must be "alive & kicking", but doesn't bother to provide needed assistance. Interesting to note he's not only advertising his products via RFsource webpage but also via eBay (!)...
The .pdf data you saw on the RFsource webpage doesn't not show the 6-conductor ribbon cable that came already soldered onto the exciter board and which is meant to be connected to the amp. and thereby control it. Only 5 conductors are used.
I have checked the photos I sent Theodoros, and can see all connections are pretty visible. Please let me prepare everything and come back with the photos, hopefully tomorrow.
The URLs below refer to the photos of the amp./"pallet" and the exciter inside the box.
The amp. is not shown inside the box yet because I wanted to use the exciter alone first, and then install the amp. for which the cooling fan is visible too, yet not connected.
In the amp. photo, a circle shows those two SMD components.
The last URL refers to the schematics I made for RFsource.
I hope those will help, and I'll most grateful, if the bunch is clear enough to explain something I may have done wrong.
Note: the somewhat crude heat sink I used for the "pallet" is in fact half of a heatsink salvaged from a old computer PSU. The PCB comes with a 4.9 mm thick aluminium plate to help cooling, but that isn't enough for heat dissipation.
Hi Carlos I see that you still haven't solved your problem, with that amplifier. I'm very sorry to hear that! And mostly because I can't help you about it, as this is not one of our products... as I've told you on telephone. However, I'm going to try to help, if its possible. For start you should leave the amplifier alone, no connection of any exciter signal at its input, while you must have a 50R load connected at its output, in case it will self-oscillate during testing. Next you will apply DC power at it, at the specified by the manufacturer appropriate voltage. I think that was 24-28V, you must check it by the instuctions they provided to you with the board. Take extreme care not to connect it in rverse polarity, as I'm not sure they have put a reverse polarity protection circuitry, and if not, that could be a reason for damaging the MOSFET's. Turniong the DC power on, there should be a very small current of about 70 - 120mA by estimation. If you have far more than that , ie 1 or more Ampers, then the one or either MOSFETs are short circuited and should be replaced by new. If that happens, replecing them is NOT so simple like just soldering the new ones in place of them, and firing up the amplifier to see if it works! There should an adjustment procedure of the idle MOSFET current, and that is something we should dicuss if needed. For now plese do check what is the current drown from the amplifier, as I said above, and inform me here. Best regard for now Sotiris Now
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.
Hi Carlos My wild guess from even when we spoke on phone, is that the MOSFET (IRF840 I think they use) has blown!!! Yes the SMT parts are resistors, I know that! The think I'm asking you to measure is the drawing current of the board, without any driving siganl attached at it. Just plain board current! If that is way more than say ~100mA then my speculation about the IRF's will be 99.999% correct! Do that measure and tell us the results. Best regards Sotiris
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).
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.
The IRF640 is indeed an RF Power MOSFET.
The L7??? is most likely a voltage regulator. Possibly an L7812CV.
Floating the ground on a voltage regulator just means the regulator circuits work without a true ground connection. It is fooled into working above the true ground of the circuit, so it can maintain the specified safe difference between its unregulated Vin and its regulated Vout. Note that this regulator also provides your bias voltage source.
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.
The one next to the board edge looks more like a capacitor and the one above it looks like a resistor. Can't really tell by the photos or the online documentation. Though I do notice a PCB foil pattern difference in that very area.
The rest of the PCB foil pattern before that SMD area seems to look the same. Your main B+ in feeds that RF choke toroid which feeds the center lead of the IRF640. If that MOSFET were short, those SMD parts would not be blowing smoke, your power supply crowbar protection circuit would kick in killing power, or your power supply's output fuse would pop.
If the foil pattern is still the same after the SMD's, one of those leads to the SMD IC chip Pin 8. Probably B+ for that chip.
Hi again OK I have located some more informative pictures of the specific amplifier, that showing clearly that the 2 small resistors are just for protection (fuse) and are 0R in series!
So if those 2 have blown there is a MOSFET short circuit for sure! So, to meke it simple you have the IRF640 as you say it is there, blown!!! Yes... I know... but that the truth! You have to replace it and before making anything else, readjust the Idq (Idle current) of it as the manufacturer says at their "manual" !!! From then you will start, and hopefully that will be the only needed repair for it. If not, then you should find why in the hell thta unit blowing up the IRF's. Also I would suggest to work it with the 28VDC required by the manufacturer of it. Working MOSFETs like these with other voltages than those they have designed to work by a spoecific circuit, is not a very good practice!
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.
Hi Carlos OK Probably the photo I've included doesn't show up from your side, although I still seen it here! As I've told you the 2 small burned SMT components are simple 0 Ohm resistors, of 0805 size I think. These are acting as fuses in the way the designer have put them there. There are in series with the +V in of the MOSFET Drain coil/transformer, so if htose have been burned, that means the IRF640 should be short between Drain (middle pin) and Source (right pin - grounded). A simple measure of it with an ohmmeter will reveal almost 0 ohm to you, and confirm my prediction of a short circuit from it. That could have happened because of extreme drive during power up! It's not my way of design things so I can't comment further about it. However if you're lucky that should be the only faulty parts. the 2 0R resistors and the IRF. replace them, adjust the Idq (Idlee current of Mosfet with NO drive at it, should be ~80-110mA) and then it should work. If you try it, start from 0 driver power and then increase no more than getting an RF OUT of 2-3W WITHOUT MODULATION!!! Just plain carrier! Wait for 5-10 minutes to watch if the RF OUT start increases by itself as time goes & temperature of MOSFET rises! If you see the smallest increament of it decrease immediately the driving power a bit, until this situation stops! Add a cooling fan fopcing air to the IRF itself & the heatsink part below it. That should make it more thermally stable to such situations. However most of these design methods are vulnarable to temperature instabilities due to high gain mosfets. And when that occurs, is just a matter of a few seconds before destruction of the MOSFETs!!! However you have at least a PLL from them, working. If the amplifier finally doesn't work, you may find some other unit to work with it.