EraSynth Micro Damaged Output - Page 1
Forum section: electronics / rf-microwave

author: Mechatrommer
author_rank: Super Contributor
timestamp: September 02, 2020, 06:51:17 pm
content: long story short, bought Dec last year, the output stage of my lightly used EraSynth Micro is dead... L4 L5 L2 (attachment 1) got pretty hot and then L5 got damaged (opened at 1.7Kohm resistance), now everything is cold but no output... possibility is GVA-83+ got damaged, but how i'm not sure, its AC coupled and i got the output on 50 ohm termination shorted while probing, but its only for a brief moment i can see it on DSO. its still survive during the probing until i turned it off, few second later i turned it on and no more output... opening it up everything is hot, and while probing, L5 burnt up as already mentioned...1) is it possible to damage an AC coupled MMIC by shorting the other end for a short moment?back calculating the output level, max output is 15dBm, thats 3.55Vpp according to my android apps here (RF Power Converter), GVA-83+ gain is 20.5dB at 100MHz, so at its input there should be 3.55V / (10^(20.5/20)) = 335mVpp of signal, but i'm not seeing that kind of level either. its from another AC coupled MMIC stage GALI-2+ (AMP1 in 2nd attachment) it didnt go that hot and its still have Vdc on the output indicating biasing still working, but no 335mVpp on the output, there's about 50mVpp signal though i can see on my DSO jumping about. since its gain is 16.2dB at 100MHz, at its input should be 335mV / (10^(16.2/20)) = 52mVpp. i sort of see that outputting from synthesizer LMX2572 + RF ATTN (F2250), so i guess LMX2572 and F2250 are ok? since AMP1 (GALI-2+) shows no gain, is it safe to say its damaged too? but how? it doesnt go hot and doesnt directly interact with user like on the output stage (AMP2). what sort of possibility of all of this unfortunate?ps: i'm contacting the EraSynth support, while waiting for the answer, may i ask here as well thanks.

author: jan48
author_rank: Newbie
timestamp: September 07, 2020, 09:08:43 am
content: The inductors getting hot indicate that your AMP2 has shorted to GND. Its input impedance is now very low and your AMP1 is feeding an approximate short instead of its nominal 50 ohm load. This would explain the low signal level that is present at AMP1 / AMP2 junction. Try to replace the damaged inductor and AMP2 . And YES ! It is possible to damage RF devices by AC coupled shorts to ground due to sudden changes in RF impedance.

author: Mechatrommer
author_rank: Super Contributor
timestamp: September 07, 2020, 10:05:54 am
content: you are very spot on.. you must be familiar with this kind of RF design and thanks for chiming in after these few days of zero interest/reply. refering to the attached pic, is internal of the GVA-83+ MMIC (almost all MMICs if not all, are similar like this) i checked with DMM, RF-OUT to GND is shorted near 0 ohm (R4), but RF-IN is about 800+ ohm to GND, so the MMIC input is not shorted, at least when its turned off, but i guess you are right, when its turned on, the T1's emitter will meet the short hence its base (MMIC's input). anyway i concluded (fixed) the repair that AMP2 is indeed damaged, with advice from Mr Adnan of EraSynth Inc, i removed the AMP2 and after that i can see some -5dB signal coming out of AMP1, luckily its not dead. GVA-83+ replacement part is on its way now from Russia, and i also ordered GALI-2+ (AMP1) from China just in case for future repair or other RF project. very difficult to find the parts online (or too expensive $9/chip), digikey and lcsc dont stock them, Mouser cant send to my country (military grade potential of terrorism i dont knowwho cares i have more advanced 8GHz ERA-1SM+ in stock), while waiting, i temporarily installed SOT-89 compatible HMC480 (with recommended biasing) into my EraSynth Micro, and now it can output somewhere at 9dB max.. cheers. edit: and i also modded the EraMicro PCB by adding a heatsink underneath (as recommended by datasheet) so the MMICs will not get very hot later...

author: andy-g0poy
author_rank: Newbie
timestamp: February 05, 2022, 11:22:38 pm
content: I bought an ERAsynth micro a year or so ago, and the same thing has just happened, the GVA-83+ failed, most likely due to me shorting it out. I was glad to see this post that confirmed the problem for me.My fault entirely, but every sig gen I've ever used inn the past would not worry about that at all. I guess the "Ruggedized Design" in the GVA-83 data sheet means something different to them :-)Managed to make a successful repair so all working again with a new GVA .I would like to do something to prevent the same ham-fisted error causing the problem again, but I have never used these devices before. My initial thought is to simply connect a 3dB attenuator on the output and leave it there, also a better quality dc block might be worth while.Would that be enough to protect the GVA, or should I consider something else?Andy

author: Mechatrommer
author_rank: Super Contributor
timestamp: February 06, 2022, 05:47:13 am
content: Quote from: andy-g0poy on February 05, 2022, 11:22:38 pmin my case i didnt do anything, the GVA just failed by itself.. anyway my GVA and inductors part arrived from LCSC long time ago, i dont have time yet to put them in erasynth. currently my erasynth was repaired with HMC480 (or ERA-1SM+?) iirc and jelly bean inductor as temporary replacement while waiting or the part to arrive, it works so far its just i believe out of spec and not as good as original GVA-83+.Quote from: andy-g0poy on February 05, 2022, 11:22:38 pmi added a plate of aluminium that works as heatsink iirc to the temporary HMC480 so it is contacted to the aluminium casing to dissipate heat. i suspected heat is causing the rf-amp to burn.

author: andy-g0poy
author_rank: Newbie
timestamp: February 07, 2022, 02:04:11 am
content: i added a plate of aluminium that works as heatsink iirc to the temporary HMC480 so it is contacted to the aluminium casing to dissipate heat. i suspected heat is causing the rf-amp to burn.I could do something similar, but the two devices are different and there is nothing in the data that says anything about short cct on the output, for either device so you may well be right.I will add a small piece of metal to the main tab to give it a little more heatsinking. I happen to have a small sheet of thin 99.9% silver that will provide a small heatsink. I'll still add an external attenuator as well just in case.I had a fair bit of trouble getting the dud amp off the board, so if your unit is working well enough - leave well alone !Thanks for the reply.Andy

author: Mechatrommer
author_rank: Super Contributor
timestamp: February 07, 2022, 03:27:46 am
content: Quote from: andy-g0poy on February 07, 2022, 02:04:11 ami think the source (erasynth) will still see 50 ohm load even if through a terminated attenuator, so it will not make any difference. attenuator only to save target device/dut... even if you can make up something from attenuating idea, you'll lose full voltage swing out of the erasynth. the safest bet is to reduce output swing (rf-amp gain) from FW GUI, or use/replace with low power low gain output amp/mmic (less heat), but again, voltage swing reduction will be permanent and flatness compromised. ymmv.

author: 9aplus
author_rank: Regular Contributor
timestamp: February 08, 2022, 09:35:03 am
content: Just to report that my unit is still working ok.Have noted the heat problem on early testing stage.Since that time, have the whole unit attached to heavy passive sink / dummy load with burned R.So far, so good.