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Re: Intermittent Loss of Pre-Driver signal
Hi Neil
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I now need to focus on some other things here for a week or two.? ?But I am satisfied that the fan modification is keeping things cooler than before.? ?And it's important to note that the fan is positioned close the two pre-driver FETs!? ?I'm reasonably sure the the increased cooling will keep this rig going for several years - and will probably outlast the rig's current owner!
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With best wishes
Steve G4ALG |
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Re: Adjusting
I'm interested in this as well. Bob W4JFA On Sat, Nov 30, 2024 at 5:30?AM Steve G4ALG via <steve=[email protected]> wrote:
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Re: Intermittent Loss of Pre-Driver signal
Hi all, Now I'm not sure if this would work. Maybe someone with more knowledge?about FET's can comment. Attached is the data sheet of the factory FET Also attached is what I found that may be a possible replacement that is more robust. Since this is an RF component, I'm not sure. Judging by the physical size of that resistor in the picture, this TO-247 case FET should? physically fit. Any comments? Factory? RD01MUS1 Possible replacement? ?IRFP260NPbF Bob W4JFA On Thu, Nov 28, 2024 at 11:28?AM Steve G4ALG via <steve=[email protected]> wrote:
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Re: Intermittent Loss of Pre-Driver signal
Hi Neil
I'm very pleased with the initial results having done the parallel resistor part of the fan modification by Richard PA7FA.? ? The fan comes on a lot more now, but will stop reliably once the internal temperature drops.? ? When doing the mod, Richard is quite right that the plated through hole surfaces need to be cleaned to expose the copper in order to solder to them.? It's a tricky process.? Great care is required.? I happened to have some conventional 33 k resistors with unusually thin leads.? This enabled me to poke the leads through the PTHs from the other side of the board, thereby providing some support for the resistor, and reduce the force on the PTH 'pads'.? ?I sleeved the resistor leads using insulation removed from some thin 7/0.2 hook-up wire.?? It's unlikely that the PTH pads are strong enough to support a leaded resistor 'surface mount' style.? Personally, I would not attempt to even solder a SMD resistor to the PTHs either, because of the small surface area of each PTH pad.? ? I did wonder about putting heatsink compound under the FET.? But, to be honest, I already had enough to deal with to solder the darn thing in place? :-)? ?The last thing I wanted was to contaminate my soldered joint with foreign stuff!? ? I'm not entirely convinced that the drive level would affect Q102 much.? ?According to the , once the rig is on 'TX', the Q102 FET (with about 3 volts on its Gate) appears to be biased in Class A.? If this is the case, the drive level probably won't affect the operating conditions of the device significantly. It's nice to have the rig working again.? It's still very new to me, so I'm still learning my way around the menus, features and functions.? Another incredible box of magic from Icom.? The TX fault was a bit of a distraction.? The only other modification I've done is the super-brilliant mod by SM6VFZ to significantly improve frequency stability of the TCXO.? ?But this is probably only of use to CW/SSB operators who use 2m and 70cm.? ?See: I implemented the modification differently, but the improvement was truly amazing for such a simple idea.
72/73 Steve G4ALG |
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Re: Intermittent Loss of Pre-Driver signal
Thank you, Neil ZL3ADC, Dave ZS1DFR, and Bob W4JFA?
Neil:? For now, I will hold off applying a heatsink to Q102 while I consider internal fan modifications.? I didn't feel that I needed to run the fan continuously, as I use the rig a lot for monitoring the VHF and UHF CW centres of activity.? ?Today, I have implemented part of the modification written up by Richard PA7FA.? See: I only added the 33 kohm resistor.? ?I was happy to let the temperature sensor detect the general internal temperature without pinning it to the heatsink temperature.? For this reason, I didn't go wild with the heatsink compound? :-) Dave:? Thank you.? ?It's much easier to keep focus when we feel part of a team. It was a team effort. ?
Bob:? A1: Yes, I used the exact same .? ?A2:?I can't find a date on the rig, but the serial number is 1002893, if this helps.? ?A3: I don't know anything about the history of this rig.? It was an eBay purchase, and I may be the third owner.? But it is in good general condition.? The rig came without a mobile mount, and there are no signs that the rig or the control head was used mobile.? But it may have been.? ?A4:? Regarding the mounting of Q102.? I also considered different ways of mounting the FET.? In the end, I decided that it was better to follow the construction method as used on thousands of production models rather than go it alone with a new approach.? I'm reasonably sure that having the tab and source (ground) plate of the FET in intimate contact with the copper foil of the PCB probably helps to keep the device cooler than if the casing of the FET is simply dangling in mid-air.
72/73 Steve G4ALG ? |
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Re: Intermittent Loss of Pre-Driver signal
Steve, Congrats! I have three questions, was the new FET the exact same part number? And, how old is this radio? Was the radio used mobile? I'm not sure about your wx but here in North Carolina inside car temperatures can be 20 degrees F in the winter, and up to 140 degrees F in the summer. I know because I monitor HVAC temperature all the time. If a radio is installed mobile you can see what I'm getting at. Something else I always wondered about is if a component like this mounted just slightly above the circuit board to allow some air circulation under it, seems to me that may help. Any comments on that? Bob W4JFA? On Thu, Nov 28, 2024, 4:37 PM Steve G4ALG via <steve=[email protected]> wrote:
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Re: Intermittent Loss of Pre-Driver signal
Thank you, Kurt KD6LZV.? That's very kind of you.
And I have some good news!? ?I've now installed the new FET, and the rig is working again!? ? My SMD efforts looks OK from a distance, but not when viewed in a close-up image, such as this one: But initial tests on the bench look good.?? It seems that FET Q102 on the Main Unit board does, through poor design, run too hot; and that my intermittent fault was entirely due to internal failure of the device due to it being over-stressed. My thanks to all who have contributed to this successful repair, including Neil?ZL3ADC,?Mark K5LXP, Geoff, and Mike ZL1BTB.
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With best wishes
Steve G4ALG |
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Re: Intermittent Loss of Pre-Driver signal
Update: New FET received & old FET removed
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The new FET arrived today, ahead of the de-solder wick.? Upon inspection, I was pleased to see that the FET 'tab' and 'source' connections are made from a single piece of metal, which is clearly visible from the underside of the device.
This knowledge helped me in two ways.? Firstly, the FET source terminal had to have a path to ground via the tab terminal, if not via the pad under the source terminal.? ?Secondly, I now had confidence that heating the source terminal with the soldering iron would probably release the tab terminal also.?? So, armed with my 50 year-old Weller TCP soldering iron, I first heated the tab, and then quickly moved to heating the gate, source, and drain terminals, thereby releasing the FET from the board.? Actually, it didn't happen quite this cleanly because the device fell apart during de-soldering.? I was half expecting this to happen. I then cleaned each pad of solder, a whisker at a time, by repeated application of a 'dry' soldering iron tip.?? Here is the result: ?
Note that the PTHs each side of the 56 ohm resistor look much nicer from this camera angle? :-)
I have since checked the FET PCB pads for continuity, and all look to be solid, with no solder bridges caused by my ham-fisted work with less than ideal tools.? Note that I still haven't removed the Main board from the rig. And here is a photo of what's left of the dead FET: I'm now planning the next part of the repair.? There does at least seem to be a good chance of installing the new FET without removing the Main board.? All suggestions would be greatly appreciated.? ?
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Re: Intermittent Loss of Pre-Driver signal
Hi Neil ZL3ADC, Mark K5LXP, Geoff, Mike ZL1BTB
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Additional Notes I've looked for a crack in the case of the FET, but the case appears to be sound.? All the PTHs associated with the FET test OK, but I will have a more detailed inspection of all tracks, pads and PTHs once I have removed the Main board.? ? Mike: I believe that suspect PTHs can be easily dealt with in the manner you describe.? Thank you. Neil: I will make another detailed examination of the PTH that you are concerned about; which is, I believe, this one: The 'gas fuel' freeze spray does have a spray tube (straw), but the tube has larger internal and external diameters than, say, the tube supplied with a can of contact cleaner or WD40.?? By spraying into a small plastic container, I can probably transfer drips of the freeze fluid to where it is needed, so I will try this later today. Once the board is removed, I will be unable to test circuit operation until it is reinstalled.? It would be nice to remove the suspect? FET with the board still in place, and then tack solder the new FET in place to do a quick confidence test before embarking on the strip-down.?? The new FET should be here by the weekend.? Actually, I ordered three of them? :-)???? The de-solder braid should arrive by the weekend also.?? I will now fabricate a custom 'FET removal attachment' for my soldering iron. |
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Re: Adjusting
I wish I could help you.? ?I had hoped that someone would have good news for you by now.? ? I assume that L701 is now broken, and that the faulty inductor means that the IC-7000 is now unusable. If the tuning slug is some kind of iron powder slug that can be removed, I would remove it.? I would then put a miniature trimmer capacitor across the tuned winding, and adjust the trimmer to restore resonance.? (Perhaps the ground side of the trimmer can be soldered to the side of the can?)? Naturally, the Q of the inductor will now be different, but the existing coil and new trimmer might still do the job well enough.? ? If the inductor in L701 has completely fallen apart, I would attempt to make a new one using a standard inductor, and modifying or re-winding the coils within the standard inductor. I hope that my suggestions here might prompt others to suggest better ideas.? Good luck! 73 Steve G4ALG |
Steve G4ALG
Bob
ZS1DFR