I appreciate the post. I have an RFG-30 that needs repair but I can't figure out how to remove the top cover without breaking it. Can you explain the procedure?
Thanks in advance.
Walt
i also have a problem with my metcal
Checking the voltage at the 74hct04 inv is only 2.5v , and the rf output is at 3.5mhz , done the norm change of electro caps which are over 15 years old etc , doing diode check on transistors , and diode showed nothing , and slowly working the schematic of mx-500 as a guide that you have here and comparing to the rfg-30 unit , so far with out any success ,
i have found that the resistance on the board over the q4 is close to dead short , even when the q4 is removed , which surprised me , will try replacing all the transistors if i can with equiv if can as a test , but i am bit lost at this point
if anyone can can verify what the sig / voltage at the test points on the board should be would be very helpfull
What i see at the moment :
1. voltage over R1 (100 ohm ) is 20V - DOES THIS LOOK CORRECT
Don't know,what is voltage on Q1 emitter?
2. Q1 collector is 6.8v
The Q1 collector is connected to L2 as in #3
3. R2 via L2 voltage is 6.8v , but on other side of R2 is 2.5v , which is appears wrong
According to the MXP500-11 circuit,D2 ,which is the only 6.8 Volt zener on the board is on the opposite side of R2 from L2,so the voltage on L2 should be higher.---different circuit?
Check across D2 to see if it is working.
4. 74htc04 pin14 vdd = 2.5v , - looks wrong
Definitely wrong,with 2.5 volts on the 74HTC04,you will have no oscillator or buffer.
Some input on this would be good guys
Cheers
Sheldon
I was going to say that the turn on/turnoff specs for use as a switch would be worse than the capabilities of the device in linear mode,but looking at the circuit,I can't see any biasing,so it certainly looks like it is being used in a non linear class of operation.
If that is so,the filtering (LPF after Q4) is probably just to get rid of any harmonics of 13.5MHz.
C24 is just a coupling capacitor,R27 & R28 constitute a 50 Ohm termination for the secondary of T1.
L10 doesn't have any resonating caps--perhaps it is self-resonant at 13.5MHz?
There are no circuit components included that can divide down in frequency ,so I suggest that you will still see 13.5MHz at the handpiece in an operational unit.
I have seen PowerFets used in "homebrew" Ham Radio transmitters,so that may be somewhere worth looking into.
P.S.:Re-read the OPs posting ,it will help more now you have reached this point.
i also have a problem with my metcal
Checking the voltage at the 74hct04 inv is only 2.5v , and the rf output is at 3.5mhz , done the norm change of electro caps which are over 15 years old etc , doing diode check on transistors , and diode showed nothing , and slowly working the schmatic of mx-500 as a guide that you have here and comparing to the rfg-30 unit , so far with out any success ,
i have found that the resistance on the board over the q4 is close to dead short , even when the q4 is removed , which surprised me , will try replaceing all the transistors if i can with equiv if can as a test , but i am bit lost at this point
if anyone can can verify what the sig / voltage at the test points on the board should be would be very helpfull
What i see at the moment :
1. voltage over R1 (100 ohm ) is 20V - DOES THIS LOOK CORRECT
2. Q1 collector is 6.8v
3. R2 via L2 voltage is 6.8v , but on other side of R2 is 2.5v , which is appears wrong
4. 74htc04 pin14 vdd = 2.5v , - looks wrong
Some input on this would be good guys
Cheers
Sheldon
- forgot to put the series cap in the handle on reassembling the cable This made the whole thing no longer a tuned LC circuit which did not warm up, not even after the generator was fixed
finding that VN0106N5 ( N ch power Mosfet) hard to find - is now been dropped from the supertex product list , and VN0109N5 is also dropped from what i can see, some suppliers on the net show some stock and i am looking to get one.
VN0106N5 - To220 - 60v @2.5A , VN0109N5 - 90v @2.5 , there are many equiv for voltage and current but not many with a @ 5ns turn on / turn off delay time , most mosfets have higher delays typicality about 40ns or more but have greater power output that i have found so far.
if you know of an VN0106N5 equivalent me know ASAP
Also note that if your looking for Q4 - IRF130 - T03 package they are on the net , Q4 on the MX500 shows a IRF 530 on the cct , and its in T0220 package , with same spec's but not fun to retro mount by the looks on RFG-30 heatsink
- forgot to put the series cap in the handle on reassembling the cable This made the whole thing no longer a tuned LC circuit which did not warm up, not even after the generator was fixed
I'm curious about that. In the original patent for the handle, there is a series cap mentioned. However, in my actual RM3-E handles, there is no such cap. It is a straight connection to the tip cartridge. A Talon tweezer i just got also has no series cap.
What handle do you have/use? A friend of mine got a newer handle (those shiny metal/aluminium thing with replaceable grips), and no cap in there as well. So unless the RFG30 is "missing" something in it's RF output section, i'd say that there is no cap required at all.
Greetings,
Chris
Talking about a delayed answer...
Not sure which handle type I have. It sure is an old one, I am pretty sure it dates back from the 1980-1990s.
Talking about a delayed answer...
Not sure which handle type I have. It sure is an old one, I am pretty sure it dates back from the 1980-1990s.No worries. As it turns out, there is no cap in there. A friend of mine checked with a network analyzer, and found no hint of a cap being there. Also, the tip detection works by biasing the tip, which in turn requires a DC path, any series cap would make that impossible. This applies to the RM3E handpiece, as well as the newer ones, and also the Talon tweezers, from what i have been able to find out.
Isn't there a feed-through capacitor instead of a series capacitor as we talked about earlier from here onwards: https://www.eevblog.com/forum/projects/diy-metcal-13-56-mhz-rf-supply/msg310381/#msg310381https://www.eevblog.com/forum/projects/diy-metcal-13-56-mhz-rf-supply/msg310381/#msg310381
Isn't there a feed-through capacitor instead of a series capacitor as we talked about earlier from here onwards: https://www.eevblog.com/forum/projects/diy-metcal-13-56-mhz-rf-supply/msg310381/#msg310381https://www.eevblog.com/forum/projects/diy-metcal-13-56-mhz-rf-supply/msg310381/#msg310381
From what my friend told me, there _seems_ to be none, according to the analyzer. Of course something could have gone wrong, and there is one and he just missed it, i don't know. After all, there is also the capacitance from the cable, so that any internal cap was simply "hidden" due to that.
Greetings,
Chris
Looking at the MX-500 shematic, a short on the gate of Q4 is normal because there is an inductor from gate to source. I found that C24 was blown in my unit which explains why Q1 fried: with C24 blown, this inductor shorts the supply. Replaced C24 with Kemet PHE850ED6100MD18R06L2 and unit works fine.i also have a problem with my metcal
Checking the voltage at the 74hct04 inv is only 2.5v , and the rf output is at 3.5mhz , done the norm change of electro caps which are over 15 years old etc , doing diode check on transistors , and diode showed nothing , and slowly working the schmatic of mx-500 as a guide that you have here and comparing to the rfg-30 unit , so far with out any success ,
i have found that the resistance on the board over the q4 is close to dead short , even when the q4 is removed , which surprised me , will try replaceing all the transistors if i can with equiv if can as a test , but i am bit lost at this point
if anyone can can verify what the sig / voltage at the test points on the board should be would be very helpfull
What i see at the moment :
1. voltage over R1 (100 ohm ) is 20V - DOES THIS LOOK CORRECT
2. Q1 collector is 6.8v
3. R2 via L2 voltage is 6.8v , but on other side of R2 is 2.5v , which is appears wrong
4. 74htc04 pin14 vdd = 2.5v , - looks wrong
Some input on this would be good guys
Cheers
Sheldon
Looking at the MX-500 shematic, a short on the gate of Q4 is normal because there is an inductor from gate to source. I found that C24 was blown in my unit which explains why Q1 fried: with C24 blown, this inductor shorts the supply. Replaced C24 with Kemet PHE850ED6100MD18R06L2 and unit works fine.i also have a problem with my metcal
Checking the voltage at the 74hct04 inv is only 2.5v , and the rf output is at 3.5mhz , done the norm change of electro caps which are over 15 years old etc , doing diode check on transistors , and diode showed nothing , and slowly working the schmatic of mx-500 as a guide that you have here and comparing to the rfg-30 unit , so far with out any success ,
i have found that the resistance on the board over the q4 is close to dead short , even when the q4 is removed , which surprised me , will try replaceing all the transistors if i can with equiv if can as a test , but i am bit lost at this point
if anyone can can verify what the sig / voltage at the test points on the board should be would be very helpfull
What i see at the moment :
1. voltage over R1 (100 ohm ) is 20V - DOES THIS LOOK CORRECT
2. Q1 collector is 6.8v
3. R2 via L2 voltage is 6.8v , but on other side of R2 is 2.5v , which is appears wrong
4. 74htc04 pin14 vdd = 2.5v , - looks wrong
Some input on this would be good guys
Cheers
SheldonJoshua what blew your C24 cap? curious!