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Re: CONFIRM JOINING
开云体育
Yes, I want to join.
From: [email protected] <[email protected]> on behalf of Karl Ei5DPB <karl.madden@...>
Sent: Monday, October 2, 2023 1:26 AM To: [email protected] <[email protected]> Subject: [Yaesu-FT-980] CONFIRM JOINING ?
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Re: 24V crowbar
Hola EA1FC !
To understand the purpose of this constant current source, first you will see that the rectifier diodes and the capacitors provide a negative supply (more negative than the emitter of power transistor). In combination with the JFET it behaves like a negative current source that can pull the base current more down as the GND output terminal. It gives the possibility for Q02, as driver,? and the power transistor on heat sink to conduct at its maximum current (close to saturation) By this way the voltage drop on the power transistor is minimized. ...and the voltage drop on teh regulation system too ! The voltage regulation is done by the transistor Q03 and the zener as reference. To get the best voltage stability, the zener is supplied? by the resistor R02. Since the output voltage is constant, the zener current is constant, and zener voltage too ! But to start the power supply the transistor Q03 has to conduct ! This is not possible without the JFET current source because Q03 is referenced at the emitter of Q02. The presence of capacitor after the current source is not a schematic error. I saw that on the PCB !
I don't know why the engineer did that ? This is odd !
Based on my experience as an electronic engineer, I was faced with solving instability in closed loop systems. And having such delay by capacitor in a loop circuit can cause instability ! The transistor of the FT-980 PA are 28V models. Supplied at 24 gives a little margin. An important remark is to have at least a 100-220 ?F on the supply line of a PA to damp current variations in SSB or pulsed CW that could cause instability of the regulated voltage. I had also a tantalum capacitor in short on the bias of the PA ! I changed all of them by 105°C aluminium. Having a variac to supply the FT-980 is possible ! I had the idea to remove some turns on the transformer, but there was too much risk of damage to the transformer... I changed also the trip point of the fan controler.... Now my FT-980 is perfect ! 73 F5RCT |
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Re: 24V crowbar
?Hallo F5RCT
I dont really undestand the constant courrent circuit Q01, even if I have known it since FP-707. I know what it does, but I dont know how it does it. BTW Yaesu has always used too much filtering capacity, FP-707 uses 0.1mF, what means litle angle of conduction and high peak intensity. Trafo suffering. So it is a good solution to reduce capacity as long as PS works. In the FT-980 I found best solution was to wire it for 234VAC and feed it with 200VAC, heath reduced a lot. I used a VariAC but if I used the radio as TX I would place an autotrafo 230/200VAC,? this PS maybe is not best Yaesu design. I think the first capacitor in 13.5V PS Q01 must be an schematic error, of course it must be placed before the FET. But all these Yaesu PS's? have one capacitor after the FET, and as I said, I dont know how it works, but it worked very well in the FT-980 TX13.5V short circuit failure (PA tantalun capacitors). Voltage went down to 3V and no damage in RF unit placed between PS and PA. I mentioned the crowbar, because I have seen it in LA of over 1kW, with transistors at 50V that die easily by overvoltage. I had this problem in one LA (4 transistors blown by 69V) and the LA is in the way to be changed linear PS for a 48V switched PS, it has a design fault and I dont trust it anymore. 73 EA1FC ?? |
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Re: 24V crowbar
After a repair I documented in other thread, I tested it and "best input voltage" was 200V (wired for 234V) for clean 100W out. I mentioned there too about the advantage of lowering voltage to increase degrees of conduction similar to reduce capacitors, the idea is to lengthen the conduction time and reduce intensity as heath os proportional to I square.
I studied the possibility of adding a resistor in series, before capacitors, but it went to over 100W resistor. This radio as it comes is extremely bad in efficiency, some 540VA in for 100W out. But besides all above, when I bought the radio near 35 years ago people were talking about the overvoltage and destruction. I have many PS and no one has a crowbar but anyway, you never know. As this radio was in the expensive side at that time, maybe someone had to find some real or unreal faults. What works quite well it is the 13.5V PS. When my tantalun capacitors in PA went shortcircuit, the 13.5V PS protection cut voltage. Otherwise extensive damage in the RF unit, in fact the best site to check that fault is in the TX13.5V in RF unit. Anyway it is a very good receiver. It is the way I use it, and the reason why the 24V fuse is out. Thanks for the idea on reducing capacity, thanks for the PDF |
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Re: 24V crowbar
Hello dear OMs,
Personally, I don't see the point of installing a crowbar circuit.?
This circuit protects against a possible overvoltage that could result from the destruction of the power transistors on the power supply regulator.
The causes of destruction can be thermal or by exceeding the current. The FT-980's two power supplies heat up far too much (it's a well-known problem!).
The transformer delivers far too much voltage if it's not configured for 2x 117 V for Europe. That's the first thing to look at!
Next, the capacitors after the rectifier are far too high. The filtered voltage is too high and the current flow in pulses to charge the capacitors reduces the transformer's efficiency.
I've modified the two power supplies by halving the capacitor values. Another problem is a design error in the control circuit which makes the power supply unstable! It is not conventional to have capacitors (C02) in the regulation loop after the current source T01 ! In attachment you will find all details of my modification. Test the power supply before re-installing ! 73 de F5RCT JMat (See my rig on QRZ.com !) |
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24V crowbar
I use my FT-980 mainly as a receiver. I have INRAD Xtal 455kHz filters.
So I decided long ago to remove the 24V fuse. I heard alarms about PA destroyed by 24PS failure destroying PA transistors by overvoltage. But I have never seen a real failure. So I dont know how needed is to install a 24 crowbar. It is simple and easy to connect it at the 24V fuse output. But I have never heard in "serious" forum about the need for the crowbar, o even about overvoltage problems. Has anybody any notice about it? Or installed a crowbar? 73 EA1FC |
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Re: FT-980 tuning issues
Any resolution on this issue? My FT-980 has the same problem. Spinning the VFO knob results more in flickering of the frequency but no significant change in frequency. If I hold the up/down button on the radio or my desk mic, the knob works perfectly (until I let go of the up/down button). Alternatively, I have to manually enter a frequency.
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Super Clean working 980 about to sell/who is interested?
Mark Randy
I was given a nice looking 980 apart with a broken attenuator shaft. I fixed that, and cleaned/lube all controls. It did not want to go to Ham fr Gen coverage and I tracked to and replaced a 40 pin IC (socketed) in the PLL . This rig works great, and I have a MD1 for it and hand mic. I really would rather sell it to someone here-before I go to Ebay..I have video of it and get great reports. Send me email and an REAL offer above $300...Randy K5SL
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Re: Yeasu FT-980 No Transmit
开云体育Wald, many thanks for the reply. I had no idea that it would not
transmit in the GEN mode. Guess I had better read the operation
manual that I downloaded. But I did try the Ham band button and
nothing also and I note that if I press the VFO button nothing
happens. It always come on at 7.000.00 right on 7 megs. I would
like to get this off my bench as I have a Drake TR7 of mine to get
transmitting and TR5 for the same reason and also working on a
KWM2A plus a Dentron DTR-200L, A Heathkit SB220 and a Drake L4b
all for me hi. All the radios are mine except this Yeasu. I will
either print the manual off or read the pdf file and try and get
more use to the radio as I would like to get it back to the owner.
I do appreciate you help. Thank you. 73, Jim VE1RB
On 2023-03-31 16:14, Wald N4PL via
groups.io wrote:
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Re: Yeasu FT-980 No Transmit
Jim, Just to eliminate the cockpit errors... you are in HAM mode, right?? Not GEN??? You probably do not realize how many times I tried to call someone while in GEN mode...? So please confirm and we will move forward. 73, Wald N4PL
On Friday, March 31, 2023 at 02:07:35 PM EDT, Jim Harris <radiove1rb@...> wrote:
Hello and I am new here. I am Jim VE1RB and I have a friends Yeasu FT-980 on the bench and have been working on it most of this week. The receiver appears to work okay but nothing out of the transmitter. I can't hear anyting on another Ham radio. I wonder if anyone has run into the problem and knows how to fix it or anyone have any suggestions of things to look at. I do have some test gear and not new at this. I appreciate any help and thank you. 73, Jim VE1RB |
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Yeasu FT-980 No Transmit
Hello and I am new here. I am Jim VE1RB and I have a friends Yeasu FT-980 on the bench and have been working on it most of this week. The receiver appears to work okay but nothing out of the transmitter. I can't hear anyting on another Ham radio. I wonder if anyone has run into the problem and knows how to fix it or anyone have any suggestions of things to look at. I do have some test gear and not new at this. I appreciate any help and thank you.
73, Jim VE1RB |
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Re: Help with very poor receive
You've made my day!? The 980 lives on!? Just to reiterate, the grain of wheat bulb fuse was blown and it saved the front end transistors.? As a bonus, it is in an easy place to get to, so I won't have to remove the board.? Additionally, thank you for the helpful link.? The part is on order. Thanks again! Ed WA2AMS On Thu, Feb 16, 2023, 1:43 PM Roger VE7LB <Roger_VE7LB@...> wrote:
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Re: Help with very poor receive
Hi Ed, If you are lucky the "grain of wheat" receiver input fuse bulb has blown. See eBay # 165671785895.
Try temporarily shorting out the grain of wheat bulb to see if receive improves. ?
Not sure why FM seems OK. May just be noise generated if the RF amp. transistor is still working. Can you hear any stations on FM?
?
73 Roger VE7LB |
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Help with very poor receive
My 980 just failed and I am looking for help:
The good: I have display & transmit on all bands
The bad: I can only receive well in FM mode.? SSB and AM are nearly dead.? I can hear very strong SSB signals faintly with AF turned all the way up.
The radio may have been exposed to a very strong 160m transmitter signal while an antenna?was mistakenly attached to it,?but I am not 100 percent?certain of this..
If I took out an RF amp transistor, why does it still work on FM???
Both the Gen and Ham receiver modes act the same... pretty much dead.
Any insight would be greatly appreciated.? I have limited test equipment.
I love this radio!? Ed |
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Re: rigctl options
Good news Fred - count me in to try the alpha version!
toggle quoted message
Show quoted text
Peter G0LQU Fred_N8YX wrote: I'm going to write an FT-980 driver for flrig. |
Karl Ei5DPB
N4PL
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