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EA1FC,

Thanks for your previous post.? I appreciate the info. I have been looking at the Q03 in the RF unit. Is that the one you meant.? It is the large one near the front corner.? In GEN the emitter and base are 12.54V and the collector is 0V.? In HAM the emitter and collector are 12.54 and the base is 11.84V.? (My power supply only puts out 13.06V and 23.9V.)? All this is with the PA unit removed.

I did power it up with the PA installed but with the RF in and out both disconnected and it did not overheat like before.

I'm still looking for someone local who might be able to work on this radio.

Happy New Year!

Bob N9IB

I don't mind you pointing out the obvious.? I will take any suggestions I can get.? I was aware of the MOX button and had checked it.? I will attempt some of the voltage checks you suggested. Thanks, Bob N9IB

Sorry for the obvious that follows, but it has happened to me before hahaha. There is a MOX knob that puts the radio in transmision without pushing PTT. If it is pushed in, the radio goes in TX without PTT. Maybe it can happen too with the VOX. Of course to go into TX has to be in HAM mode. So if any of the events are "ready" as soon as you go in HAM the radio goes on TX. So check that you dont have MOX or VOX ready to activate TX.

In case the radio goes on TX when in HAM, you lose reception. As I told you it had happened to me during repair. ?Why does it not receive? SILLY it was in transmission? because MOX was ON. Some modes FM FSK or CW can produce full power

Because the PA (alias "the brick") has only 3 connections, 24V for finals, 13,5V for drivers, and (switched RX/TX) TX13.5V for predriver Q01 and bias 13,5V>8V>0.7V with the two voltage regulators. It is very pasive just follows the orders, but has no decision.

You can test the PA outside the radio. and measure intensity. TX13.5V in mine was about 200mA. 24V for finals, and 13.5 for predrivers should be almost 0 without TX13.5V (reception). I have not measured intensity because mine worked OK, but I think that 24 and drivers should take about 1A each in TX (no signal out) and nothing in RX.

Check voltage out of Q01 in RF unit in RX and TX with PA out. That is the TX13.5V output to PA.

It inhibites (cuts) TX13.5V in GEN and allows transmission in HAM, I mean ALLOWS, because RL01 in RF unit is the one really switchin RX/TX. In a very brute way Q01 in RF unit can be bypassed, it only inhibites in GEN or TRANSVERTER, in other words KILLS the PA even if RL01 goes in TX, RF unit Q01 stops TX13.5V to the PA. As all is OK in GEN, I think Q01 in RF units makes its job cutting TX13.5V from RL01, even if RL01 moves from RX to TX, Q01 stops 13.5V to PA. Only when Q01 in FREE (HAM mode) you get the problem. You have to check Q01 output. If you get 13,5V in HAM RX the problem is in RL01 ?welded allways in TX? I think this is the first thing to do, and it is easy. Just disconnect the PA and open the low cover to have access to RF unit.?

As you see, nothing should change in PA unit as long as the radio keeps in RX.

Check MOX and VOX. and relay RL01 in RF unit. Maybe does not cut TX13.5V out in RX mode. Easy to check in Q01 in RF unit. just in a front corner, a large transistor, acting just as a switch.

Even so, you have a problem, because even in TX should not smoke. So when (AFTER) you clear the first part (RX/TX switching), you have to check the PA. I think something makes drivers and finals high intensity. Maybe some are damaged (short collector-emmiter) or bias that should be about 0,7V from second regulator, is extremelly high ?8V? and makes drivers and predrivers crazy.

I have repeated myself a lot hahaha, but I think the message it is clear.

73 EA1FC

This is definitely not a Tx/Rx issue.? I have not even attempted to transmit since Nov. 14th when the first problem appeared with the C20.? Everything seems OK until I switch from GEN to HAM and then it gets hot fast.? At this point I'm stumped.? Why it gets that hot in receive I do not know.

There is no one close to me that can repair this that I know of.? I would have to ship it to someone and hope they have experience with these radios.? That's why I have been doing the things I can do to try to troubleshoot this.

As far as I know, nothing changes in the PA while in reception HAM or GEN.

Maybe you mean in transmision. Then voltage TX13.5V appears (13.5V line is allways present for drivers and finals collectors). After the fac mod, predriver Q01 takes from TX13.5V too. This TX13.5V voltage is reduced for bias to 0.7V in two cascaded regulators. If they are shorted an extreme high bias can pass to the drivers and finals. And some disaster may happen. TX13.5 comes from Q01 in RF unit, via RL01 in RF unit. Check both. They made the Rx/Tx conmutation.

If a tantalum capacitor in Q01 collector shortens and the 13.5V PS protection does not work (mine lowered to 3v), RL01 may have damaged by overcourrent, because Q01 in PA takes power via this relay once the fac mod has been made. In schematic PA Q01 takes from 13.5V line, after mod it takes from TX13.5V via RF unit Q01 and RL01.

But all this is related to Tx/Rx, not with HAM/GEN.

I think the mod was done to avoid PA Q01 to autoscillate in Rx. If you get TX13.5V line with voltage during Rx (RF unit RL01 stuck), the whole PA can oscillate madly.

If it gets hot in HAM Rx... you have a problem somewhere.

I replaced the two resistors in question and now some else smoked.? It worked fine in GEN but when I selected HAM it smoked briefly.? I cannot see any damage or figure out with component caused the smoke.? It still works fine in GEN but in HAM it gets hot fast and smells hot.? Still trying to determine the source of the heat.? It is something in the area of Q05. A non-contact thermometer quickly shows a temperature of 180 F in that area in HAM mode.

73 N9IB

I believe they are the R16 and R18 shown in the parts list as metallic film, 1W, 1.5 ohm.? They are right next to transformer T02.? They appear to run in parallel to C27 and C29 caps.

73 Bob N9IB

L05 it is not missing. Just changed place :)

L05 feeds Q01. In the schematic takes from 13.5V line. That means Q01 has collector voltage all the time.

The ?factory? mod changes L05 to feed from TX13.5V (only in transmision) you can see it in your radio feeding with a YELLOW wire that takes from the regulator Q06 input. A post in which the yellow wire connects with the red TX13.5V. Therefore L05 in somewhere in the air close to Q01 ferrite collector coil.

I guess you have not replaced a new L05 in the position of the schematic without removing the yellow wire, otherwise you had connected together the 13.5V and TX13.5V lines.?

Maybe they changed L05 to TX13.5V to avoid Q01 oscillating in reception. In TX it is piloted by RF signal.

Can you be more specific about the resistors that smoked?

73 Frank EA1FC

Hi EA1FC,

I replaced the C20 which had blown and the C18 like you did.? I got some 10uF, 16V tantalum caps from Mauser Electronics.? They are yellow and about the same size as the originals.? I also noticed in your picture that the L05 inductor that shows on the schematic is missing. Mine is that way too.? I put mine back together and it smoked again.? This time I can see two burnt resistors by the T02 transformer. (See picture)

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

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
?

Hi Robert,

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

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

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.

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

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

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 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

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