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FT-980 no power out in HAM mode

After? many years iddle I switched on the FT-980 and it did not transmit.

To make a long story shorter, the transmissión is inhibited if a trasverter is used or in General mode. It does it cancelling voltages to PA bases (PA cut).

Q01 in RF unit makes the control job and Q03 acts as a switch.

I measured 5V in its collector and 3V in the emisor output (should be 13,5V/13V).? I thought upwards the relay RL01 had a bad contact. It changes Rx/Tx 13,5V or 0V

But then I measured only 20 Ohm load in the output of Q03. So suspicion changed to PA. 600mA is far too much for controlling base bias.

The PA was receiving from RF unit 3V instead? of 13,5V for the bias internal regulacion. 13,5V>8V>1,3V. The PA includes a 7808, plain diodes? and zeners for the job.
PA is full of tantalum capacitors. 2 outside in fan control and 7 inside.

I opened all but it is beyond my capabilities to desolder heavy things in PA to access the capacitors.

Maybe I can cut the first capacitor and place it in the RF unit output to PA and maybe even the second capacitor after the 7808. But it is impossible for me to go beyond that. Most of the tantalum capacitors have ceramic in parallel... maybe I can feed PA and bias control with 13V and start cutting tantalums until I find a reasonable iddle courrent. Distorsión? Maybe if not enought iddle...

I have not read about a similar problem. Waiting what to do... Maybe move the FT-980 where it has been the last 20 years. It is a good receiver. I replaced the Murata 2,7kHz 455kHz Width control with a Quartz filter 2,1KHz and now it is very effective.

I plan to test the PA outside the 980, at least voltages and intensities to confirm the tantalum disaster.

73

Continuing the story

I am still looking inside the PA. This rig was bought in 1987 from a store when it closed, and might have had a previous owner.

Today I found a modification not documented anywhere (as far as I know). I mean modification because it can be seen the place in the PC where components were before, choke L05 in PA cut from original place (13.5V), and moved to TX13.5V.

The predriver Q01 takes now collector voltage from TX13.5V line, that is the bias (TX ON) voltage. There is another 13.5V line for driver's collector. That is a mod. In the manual the prediver and drivers take voltage from 13.5V all the time. TX13.5 in only live when "transmision and HAM and not transverter used". 3 conditions. The logic is in RF unit.?

So before I start cutting tantalums, I better look at Q01. BTW it is not thermal connected, the screw has never been there.

The fact that Q01 takes power from TX13.5V instead 13.5V may have consequences because for base bias not much intensity is needed, but for Q01, I guess maybe 200mA are needed. I dont know because this mod was done or who did it. Maybe self oscillation, because same mica capacitors around output coils seem a bit toasted.

In short, a new protagonist, Q01 missing the thermal connection it never had, but should have had. I was centered in capacitors, or any of the two cascaded TX ON regulators (BIAS), from 12.5V to 0.7V. ?

73 EA1FC

Today I have seen a video of a FT-980 PA repair with the Q01 mod, taking collector voltage from the TX13.5V. So it seems to be factory made. In my rig the lacker on the screws seemed original. So I guess it is original, even if it is not documented. Q01 had no screw either.

Damaged was a tantalum capacitor in Q01 collector blasted. Another one in 13.5V for driver's changed too. Most of other capacitors are in base bias line carrying 0,7V, so in the video were left unchanged. I guess because some were not easy to change (cut and weld from top) and removing the whole board was out of scope.

Waiting for a PS to test PA TX13.5V behaviour.

73 EA1FC

Thanks for the updates on your progress.? I have a new-to-me FT-980 that only receives on 80 and 20 meters.? It also has a loud squeal when attempting to transmit.? Please continue the updates, I am very interested in your progress.

73 N9IB

Hallo N9IB

Regarding the no reception, I have not clear the situation. Does it show frecuencies in display? How in GEN?. Only in HAM?. There can be some things. if it is only in Ham. I would first discard problems in the RF unit. I am not an expert, but there is some info regarding problems in the HAM band filters due to electrolytic capacitors in the 11 band filters losing capacity. Much easier is to check connectors J10 and J11 (push and pull) (they are close to Xtal filter). In general it may help to move out and in the connectors in this 40 y.o. radio.?

When you have the radio opened and upside down to show RF unit, check in RF J015 in radio front, between attenuator shaft and a large transistor, this transistor inhibites transmission in some logic circunstance. Red cable in J015 coming from RL01 (input to transistor)? should have 13.5V on transmission. White cable is TX13.5V to PA I have been talking about. Checking voltages in this J015 it is important. White cable (output to PA) has a lower voltage than red cable (input from RL01). In case of overcourrent in PA, the voltage can be low, and the relay? RL01 (switches 13.5V Rx/Tx) can be damaged.

If you look in youtube for a video on "Reparacion FT 980" (in Spanish) you can see some damage and repair in PA.

Overintensity in 13.5V PA can blast capacitors (video), and even trip the overintensity protection in 13,5V PS, where Q01 is some kind of constant intensity source to comparator. In this radio as the real power is in 24V, the 13.5V PS is not that powerful. That is why it is important measure voltage in white cable of J015 of RF unit when Tx allowed (HAM and no transverter). If the 13.5V PS is cut to very low voltage, all voltages are low, and the radio can make anything it likes. So... Check that voltage...

And closing the circle, the mod in PA so PA Q01 takes collector from TX13.5V instead from 13.5V, means some added ?200mA? intensity to RF Q01 and RL01 originally designed to handle only PA bias intensity, but it seems this mod has been made at factory. ?To avoid autoscillation of PA? Might be feedback between Q02 & Q03 to Q01 via the 13.5V path. So they changed Q01 to TX13.5V line, physically far from 13.5V path. Who knows... I keep in mind from the PA in video mentioned that the blasted capacitor C18 and the "cut and moved" (green wire) L05 choke are in Q01 power path. Changed from TX13.5V to 13.5V. ?Coincidence?

Unfortunately it is difficult to lift the PA board from the aluminium radiator to check/change capacitors in PA, like C30 330uF in 24V or the many tantalium in 13.5V and TX13.5 lines. It is all very compact. But the aluminium sides where 7808 is, can be easily dismounted to have lateral access and weld new capacitors on top wires of damaged capacitors (not easy in all cases)

73 EA1FC

Hallo N9IB

Speaker noises in Tx hidden in my long speech. I make it short.

If 13.5V is "killed" "protected"? to 3/4V due to PA problems, the radio makes funny speaker noises in TX as you report. So check that TX13.5V in RF unit J015

On Mon, Oct 24, 2022 at 01:50 PM, radio_ozu wrote:

Regarding the no reception, I have not clear the situation. Does it show frecuencies in display? How in GEN?. Only in HAM?

By that I mean that in those bands I get background noise (static) but do not receive signals that my other radio can receive with no trouble.? The display seems to work fine.? Happens in both GEN and HAM.

73 N9IB

You say only receives "on 80 and 20 meters". With a 9MHz filter that would be tipical? problem in a convencional radio using 5-5.5MHz VFO. But I have not gotten into the frequency mix of this receiver yet. I will try to check. I guess it needs a frequency adjustments in case one Xtal is not oscillating, and is needed for other bands.

In the meantime look for voltages in RF unit J015. When transmiting in HAM mode it should be something like 13.5V (red wire input) and 13V (white wire to PA) this is called TX13.5. It is very easy just open the lower case, J015 is easy to see. If you dont have over 13V in TX13.5 you have a problem. Then unplug J015, plug it turn it 90? ACC to keep the red wire? to transistor, white in the air,? and measure again. pluged 90? (no output) and un pluged. This can tell you if you have a problem in transistor or in the PA. In case of failure there are only three posibilities
1.- Damage source (13.5V PS or RL01 in RF unit)
2.- If RL01 delivers 13.5V Problem in RF Q01 if no voltage out TX13.5 disconnected
3.- If output of Q01 was over 13V with white wire of J015 removed, then problem was not in RF unit. Too much intensity in PA. Has to be handled soon, so it does not damage PS o RF units, See blasted tantalium in video. In this circunstance of extreme 13.5V >>> 3V when PTT is ON the radio does not transmit and strange sounds can be heard in the speaker. Don't insist or something will blow up. In the meantime place J015 turned 90?ACC or remove it, to make sure 13.5TX does not come to PA. Anyway there are other capacitors in 13.5V line of PA. So better think about inmediate open/check of PA. It is easy to remove, only 4 screws in the back and the whole brik goes out. Before the grilled cover side to side has to be removed, for what you have to remove one by one the radio covers. I always replace one when I remove the other. Take care not to damage wires, specially the one to the RAM battery.

Take in mind that this transistor RF Q01 is a switch, without a mod (Tx in GEN) this transistor RF Q01 is a switch to allow only 13.5V to pass to PA with MOX ON (or PTT) when transmission is allowed (HAM and no transverter). It cuts in Rx, if transverter, o in GEN.

Today a went to a friend that has a lab PS and as expected it showed a short cutting in regulated 0,5A, obvious too much for the bias line, even with the predriver taking from TX13.5V. All was tested very provisionally. Short voltage was 3V, similar as measured in RF Unit Q01 when connected there. And consistent with 20 Ohm measured in PA TX13.5V line.

Next step is to work comfortably. I guess I have to cut the mod that gives volts to PA predriver, then cut regulators, and in the end start destroying tantalum capacitors on 13,5V. Job for Freddy Krueger, cut and test, cut and test.

I hope in some moment the intensity goes to normal. Some mA for bias and maybe 200mA for predriver.

I am not testing 13.5V line to drivers. I have seen a repair with blasted tantalum in TX13.5V. The one in the 13.5V (drivers collector) was changed too. Leaving the ones in 8V and 0.7V. In case the problem are the capacitors, I think I will change the one at 8V between both regulators 13.5>8>0.7V to vias.

73 EA1FC

New advances.

I lifted (cut) from T13.5V the choque L05 feeding predriver, and TX13.5V intensity went down to 250mA. In this line only transistor Q01 or capacitor C18 can produce the short. I guess it is the capacitor.

At the same time I noticed 3,3V zener D01 has only 2,9V. It has capacitor C13 in parallel. Therefore voltage Bias for predriver is low. In short whenever I look close to a tantalum I see they are not fully OK. I dont pretend to repair it "as new" but at least to clean possible dangers upwards as a damaged tantalum mean a short. I guess I will not touch the ones in very low voltage lines, 0.7V and similar. But I think I have to take care of those directly on the 13.5V lines from the PS. Specially TX13.5V because it passes a relay in RF unit that can be damaged. Luckly the PS intensity protection worked (I hope) when I measured only 3V in the relay output.

I dont have the right tools neither the eyes for a good repair, but I hope I can make it functional.

I have found other tantalum in IF unit, but I guess they are not in essential places, NB f.i. So I dont know if I will change them. A pitty because 30 years ago I installed 3 IF filters, and then if would have been easy to change tantalums in that board. Now 30 years later, I am 30 years older...

73 EA1FC

?I have cut C18 positive leg in Q01 collector. Leaving some mm of it to be able to solder new capacitor. Negative is surface soldered, large area.

Removed capacitor show 14.5 Ohm in both senses. No capacitance. BAD.

Before I measured 19 Ohm both senses between collector and emisor. Emisor goes to ground with a 4.7 Ohm resistor consistent with above. Now Q01 shows OK.

Now I have two option, replace C18, close and try, or keep checking capacitors.

In the only detaliled video in youtube the spanish OM changed this capacitor (obviously BLASTED) and another in the 13.5V constant voltage to drivers collectors.

To note that all others 10uF capacitor are identical in aspect and 16V, and might be more or less OK. This is differente color, 25V, and much larger.

It was easily accesible removing the side plate to wich nothing is attached, even if it has a hole to screw Q01 and use plate as radiator. I will do it. For what I need a mica, now there is only some paper in the aluminium "radiator" never has been a screw there, the paper does not have hole.

Now total power intensity in TX13.5V is less than 300mA. 50mA for Q01 collector. 250mA for bias of finals ( I hope in these 250mA there are not included some mA for a bad capacitor), there are 4 of them in this line. And another 4 capacitors in 13.5V constant voltage for drivers collector.

All above could have been better documented with photos, but it seem it is not possible to add them.

73 EA1FC

Final, radio working OK. Puts out 100W.

Lesson learned. Anyway the broken capacitor was larger, 25V instead of 16V and different color otherwise 10uF like the others. From factory from sure. I guess why. Maybe programed obsolescence hahahaha

73 EA1FC

I have added some photos related to the text. Photos have a short name

73 EA1FC

I initially said it only received in 80 and20 meters.? It does in fact receive on other bands but only for very strong signals.? It's like the RF gain was turned down but it's not.? The S-meter never moves either during reception.

N9IB

To N9IB
Your problem it is hidden in my former title, and maybe other members will not find it, maybe you should open other thread. I have opened a new thread regarding malfunction in the first 10 minutes after switch on the radio.

I asked about reception in GEN because the band filters in RF unit for HAM or GEN are different. And the electrolytic capacitors in the HAM filters have given problems sometimes, so the first thing would be to discard the filters. As you say the lack of reception is similar in both modes, the problem it is not in the filters themselves. Once filters discarded, comes teh voltages that selects the filters.

So you have to check J10, J11 (HAM), J12 (GEN/HAM) and J13 (GEN) just pull them and push them. J13 should have 13.5 in the selected band and 0V in the others. J10, J11 0/4V, and J12 HAM/GEN 0.7/9 and 0.7/8. I am a bit lost in the logic and uP. But I think I am right. May someone know better.

Another problem is than the band filter is OK but the logic HAM/GEN is opposite in this case.

But you can check in the filters that the diode are ON, even if when testing the reception is affected by the voltage testing

So I think this is the first thing to do.

I dont know how to analyse the logic that generates those voltages, uP and so on. I am old and I manage better tube radios hahahaha

But first thing is to cleac/ check voltages in those connectors, before I told you to lift them and put them to clean them. But it is easy to check that the correct voltage arrive to the band, and.... no voltage to the other bands.

Maybe you should copy this text if you find it interested, for your new thread on your problem. Here is hidden for most.

After I commented with a friend about the tantalum problem in PA predriver, he look at a FT-107 bought in a lot (interested in the tuner FC-107) he look in the PA and found predriver tantalum blasted too.

PA in these radios are very very similar.

In the FT-107 it is 16V (blue), and in the FT-980 they changed it for 25V (red), the only 25V tantalum on the PA the remainder are 16V (brown)

Curious that Yaesu changed voltage rate in the FT-980 to 25V. Maybe had some feedback from other radios. I guess FT-707 is similar. And there are the first transistor finals radios.

73 EA1FC

I finally got this radio working after re-reading the manual and adjusting several settings.? It worked for one day and blew a capacitor in the PA unit.? The capacitor is brown and the schematic lists it as 10uF and .50wv.? In the diagram it also has a T in parentheses like (T).? Is that tantalum?? I want to make sure I get the right one to replace it.? Any help or suggestions would be appreciated.

73 N9IB

Hi Robert,

I was just re-reading this thread and noticed your comment about the missing screw in Q01.? Mine had a plastic machine screw in the hole but no nut was on the screw. I took the screw out before taking the picture. You can also see my blown C20 capacitor.

73 N9IB
?

I thought I had uploaded the 10uF capacitor. I placed a plastic screw in Q01

This capacitor is specially prone to fail. 4 that I know up to now. There are many more in the radio, bur this one besides being of higher voltage is the one that fails. With different color, maybe another maker

73 EA1FC