Yaesu FT-7 No Transmit

[Sufferinghusban]

I purchased an old FT-7 for parts, but in all honesty the receive side this radio is so good I cant pull the parts I want! Tested the TX and nothing coming out. Put it on a dummy load and tested what I can on the finals MRF433's. They have 12v on the base, and when keyed I get about 0.7v on the emitter. I have a receiver setup near the FT7 and when I key it in CW I can hear a tone coming through on that freq but only very weak. I have never touched transisters like these before, but believe they are blown and I have to replace them. Basically just looking for some advice on removing them as they are the oddest thing I have seen in a while. Thanks.

[mickm3for]

Hi the transistors are 2sc2099 in the 50w pa they contain beyllium oxide this is in the heat sinking within the transistor case do not put force or excess heat as this will cause the top to become adrift exposing the oxide this is toxic.
the col is at 12v Bace is a low bias voltage via a regulator this is Q2205. The driver is Q 2202
place an amp mtr in series with connection final 13.5 v this should show the standing current when on tx and increase with modulation
As to removing remove the 2 screws and carefully remove each of the 4 legs 1 at a time do not subject force to transistor body i find a thin blade helps to lift tab
when used with soldering iron.
the cut off tab is the c one op. is the b the other 2 the e

[G6Tanuki]

Quite a number of transceivers from that era had the ability to bypass the HF PA and instead produce a low output (a few hundred Milliwatts) to drive a transverter so you could operate on VHF.

The idea was that you bought your HF-transceiver as a Class-B-licensed ham, for use with said transverter on 2M/70cm, but then when you got your Class-A licence you could operate on HF too.

Check there's not some 'special' wiring of a facilities/interconnect plug on the back!

[mickm3for]

That is a point my unit is a 7b it has a 50w pa no lo power plug etc but has a drive pot this varies from about 5w to 50w

[HamishBoxer]

Using de solder braid may help if these are soldered to the circuit board.

[Terry_VK5TM]

No, you definitely shouldn't have 12v on the base of the MRF433's.

And 0.7V on the emitters is strange as they are directly connected to the negative line - are you sure you are probing the right leads of the transistors?

And for reference, these early models had no low power output option for transverter use etc.

[Sufferinghusban]

Thanks for all the info guys. This is a FT-7 not the Bravo. In all honesty I am flying blind with this. I can't find a circuit diagram for the board. There are ones about for the Bravo but not the plain Jane 7 that I can locate. All I know is that I have 12V permanantly one one of the lines, and the line opposite it gets close to a 0.7v when I key the mic on CW. I have been trying to find where I can adjust the RF output as I thought it may have been knocked down as well, but no such luck, nothing about that I can find. This radio has been modded at some stage to get it onto another band, probably 11m. If that was the case they probably had the RF turned up all the way, as some people did back in the day Hmmmmm.. Hmmmm..

I more than likely have the E B C confused as I can't tell what is what by looking at it. There is so much solder I can't find the tab with the corner cut without pulling them. With no diagram for it as well it makes it difficult.

[Terry_VK5TM]

Here's a link to a zip file file with the manual and copy of the schematic from my Dropbox.

I coloured the supply lines to make it easier to follow.

https://www.dropbox.com/s/y76b60depenvbk8/FT7.zip?dl=0

The link will expire on the 31 May 2019, but if anybody else wants it after then, pm me and I will email it to you (approx 7.5Mb file).

The permanent 12v will be the collector and the 0.7v line (if opposite the 12v one) will be the base. Other two are emitter.

[Jon_G4MDC]

If your MRF433 are proper Motorola ones then locating the collector is easy.
The batwing "M" is placed adjacent to the collector tab.

The base is diametrically opposite leaving just the 2x emitter tabs either side.

[Sufferinghusban]

Just a quick thanks for the info. No time at the moment to have a good look, but will later on. The schematics will come in handy for sure. I know I have been getting the legs of the transistors mixed up. The photo posted might be off an FT7B as I only have two RF finals.

Originally Posted by Terry_VK5TM

Here's a link to a zip file file with the manual and copy of the schematic from my Dropbox.

I coloured the supply lines to make it easier to follow.

https://www.dropbox.com/s/y76b60depenvbk8/FT7.zip?dl=0

The link will expire on the 31 May 2019, but if anybody else wants it after then, pm me and I will email it to you (approx 7.5Mb file).

The permanent 12v will be the collector and the 0.7v line (if opposite the 12v one) will be the base. Other two are emitter.

Terry, thanks for the info, at least I can identify the lines now. Are those voltages correct though?? I want to ensure that the power hasnt just been turned all the way down before I start pulling things apart, but not sure what controls the RF out.

[mickm3for]

Hi. Don't forget to peak the tune control as this controls the tx drive circuits Mick

[Terry_VK5TM]

The collectors of the PA transistors are permanently powered whenever the set is turned on, so you should see very close to whatever the voltage of the power supply is, on the collectors all the time.

If you look at page 2 of the coloured schematics, just to the lower right of the 10w amp module, you will see VR2105, which adjusts the collector current of the PA transistors. This will have some effect on the collector voltages and output power.

Re the base voltage, again on page 2 in the 10w amp module schematic, you will see diodes D1302 and D1303. They are connected to the centre tap of the transformer feeding the bases of the PA transistors (along with the bias voltage supply) and ground, being forward biased, you will see a voltage of about 0.7 volts on each base.

A common problem with both FT-7 versions is that the various plug in modules can get tarnished connections and also move slightly causing connector alignment problems. It is a common trick to remove and re-seat these modules to cure these various problems. No Tx can be one of these problems.

Do not be tempted to wipe fresh solder over these connections either, but rather clean them with either a glass fibre brush or old fashioned ink rubber or similar (be careful, as these things get older, the pads have a tendency to lift if treated too roughly).

If you haven't already done so, check the Tx/Rx relay contacts.

[Sufferinghusban]

Terry If I am reading correctly, then the voltages that I am reading on the RF finals are ok then I have pulled all the board and cleaned them with alcohol and put them back in. Made absolutely no difference to the power problem like you said. I am a bit uncertain how to proceed, what would you suggest?

Originally Posted by mickm3for

Hi dont forget to peak the tune control as this controls the tx drive circuits Mick

Mick, using the tune control doesn't make any difference unfortunately on the TX side. Best I can do is tune in the RX to the best signal. One of the bands I could get a tiny amount of power out of, as in the needle would only just move a fraction. I can hear a TX tone on a local receiver but it's nothing great. From Terry's reply, it sounds like the RF Finals have the correct voltage on them but nothing is coming out of them worth noting. At this point I don't know if the finals are blown, or someone has turned the RF right down. From what I understand I should be able to adjust the RF output by using the VR 1501 access hole on the rear panel, but it doesn't want to turn. Its a of a spot to look in, let alone get a fine enough driver in to turn it. I am open to any advice at the moment. Cheers

Terry VR2105 is one that I have been looking for and cannot locate. It came up in some info I found last week, but I cannot find where it is located. I was going to look at VR1501 as it is supposed to be accessible through the rear panel but it's not looking promising either. I have not checked the relay contacts. The relay is working but no idea if the contacts are clean. I will tackle that next. Any advice appreciated, I am running out of what to do. Cheers

[Sufferinghusban]

I cleaned the relay contacts and they all appear to be fine.

On the RF Board I did notice something this afternoon. I setup a receiver on the tx freq of the FT7, and proceeded to check the voltages again to get my head around the RF finals, and what leg was what. When I had the radio keyed, into a dummy load, I checked the voltage on the C1589 on the RF board and as soon as I touch one of the legs the transmitted signal is amplified enough to give me an S9 on my receiver nearby. Without touching it, it is barely audible. No reaction to the signal from anything else. No noticable voltage out the other side of the finals. It still didnt draw any extra current, but made the signal stronger for sure. I am fairly certain that things are well to that transistor, but after that nothing happens. I am only using a digital multimeter for testing. Terry if you can confirm that the RF finals have the correct voltages on them ie 12v and 0.7v I can take it that the finals are probably shot. Your assistance is greatly appreciated.

[Terry_VK5TM]

Normally, if the PA transistors are shot, it will take out the fuse as soon as you turn the set on (they seem to more often than not fail short circuit C to E rather than go open circuit).

Did you check both relays?

RL2101 - Rx/Tx voltage switching and is in the body of the set.

RL2102 - Aerial changeover and is hidden behind the back next to VR1501.

Next on the check list is the switched Tx voltages of 13.5V and 8V which are routed to several modules. It would appear the 13.5v one is OK as you are getting the 0.7v on the bases of the PA transistors and it is derived from this line.

These checks will not be easy to do without extender boards, so you may have to pull a module out, solder a length of wire to a suitable point and refit the module (some of the check points are under the band switch and hard to get to).

Next would be to build a simple RF probe for the DVM and back trace from the aerial socket through to the Mod/Demod module while in Tx mode (use CW mode).

It will only give you a relative measure of RF level, but if that jumps up as you go back along the signal chain, it should pinpoint the problem area.

Another common problem if a set has been attacked by a CB'er is the low pass filter coils in the LPF unit, but that is normally only on the 10m band.

[Sufferinghusban]

Terry, the aerial changeover relay I did not touch. I gather the rear panel has to come off for that? If it's not the RF finals I feel it may be further along past them. I suppose in a sense when the signal got louder when I touched the other transistor on the RF Board I was basically giving it an antenna to send out to. Does that make sense? If VR1501 is the ALC adjustment I have been trying to turn it but no luck. The rear cover has to come off to just see in there, and get a screwdriver that will fit it as it appears very fine and with no light I can't line up a driver to adjust VR1501.

The unit has been modded, either for 10m extended or 11m. The 10m crystal is switchable to a blank crystal socket, but it is out of play. I am not testing on 10m at the moment but it appears to be normal. In saying that things may have been tweaked and left.

As you may have guess by all the questions, and dumbness, this is all new to me. I know the basics but never delved into it like this, however I love a challenge! If I can get it working again it will be a great personal accomplishment. I will look up how to make an rf probe and see what happens. I gather with that I should see something coming off the RF board? Thanks for all this.

[Sufferinghusban]

Update. Removed the rear panel and got good access to the relay. It was working but pulled it and gave it a clean. Nothing looked unusual. Had a good look at the VR that I was having trouble with. Managed to get it to move. Buttoned it back up and tried adjusting the VR through the access hole on the rear panel. It made no difference to output at all, so I put it back to where it was.

This time I put the receiver on and tested the FT7 on transmit CW/LSB/USB and I can hear it on the receiver and all modes working. Sounds quite clear on SSB. Just no oomf!

I am looking at getting a hold of a an RF Probe as suggested. At the moment the radio seems to be doing what it is supposed to just at very low power. I have not been able to locate the other VR that was mentioned. No hints of where it is located anywhere! Humbly awaiting advice. Cheers

[Terry_VK5TM]

VR2105 - > page 19 of the manual, left hand picture, second item from the top.

It's in the PA module, again with a screwdriver access hole on the top.

Beginning to sound like the problem is somewhere between the input to the PA module and the antenna socket.

So that leaves us with:

the PA module

band switch - as in any rig that uses a band switch such as this, dirty/tarnished contacts are common.

LPF (low pass filter) module - as mentioned, burnt out coils is most common on 'got at' rigs. Note that the LPF module is only on the Tx side, not used on Rx.

ALC module - only thing I can think of that can go faulty in there is the diodes and T1501, although I can't say as I have heard of that happening.

Antenna socket - what is the receive side of things like? If that is OK, it would eliminate the antenna socket, but a visual check for a broken wire would be an idea next time you're in there - has been known to happen and will throttle the transmit side right back.

Re the VR on the back panel, did you by any chance think to do a meter check on it to make sure it wasn't faulty.

[Sufferinghusban]

Terry, what has me thrown is that when I listen to this radio transmitting it is perfect. It has no power, and the receiver has to be near it with no antenna or you wont hear it, but the CW signal and the USB and LSB voice is clear as a bell. The receiver is about the best I have heard. I have other radios that dont receive as well as this little beast.

I did check the antenna socket and it is fine. The radio is off freq a bit but is adjustable by the front panel adjuster. That side isnt worrying me at the moment.

I have not tested the the meter as such. On rx its doing its bit with strong signals. On TX it barely moves, maybe a needles width. Tuning it does nothing.

Just realised why I couldnt find VR2105 through an access hole! The top cover is gone and that had been staring me in the face from day 1. Moving that VR on TX did nothing either. So the two VR's that are supposed to affect RF out do nothing at all. Yet I am still getting a very weak (but perfect) signal out of it. Today I put it on the antenna, and there was not enough of anything coming out to activate the antenna tuner or the meter on it. There is just enough coming off the radio to allow the receiver next to it to hear it.

Coming back to my playing about before, when I touched certain items on the RF board when transmitting with my multimeter probe the signal increases three fold or more, but still no normal power. Its as if something is blocking the power getting out to the antenna.

VR2105 was turned all the way counter-clockwise when I found it. The VR on the ALC was tight, and turning it didnt achieve anything.

I am still leaning towards the PA ALC areas, but will try to look at the Low Pass Filter Module to see if anything obvious. Cheers

[Terry_VK5TM]

It's beginning to sound like your first hunch about the PA transistors may be correct.

You can do a meter test on the transistors by lifting a few component connections, but you will probably have to remove the PA module to do it.

The connections to lift are:

Both ends of T1301 that connect to the bases of the transistors.

R1308 and R1309 (15 ohm resistors that connect between the bases and ground).

Both ends of T1302 that connect to the collectors.

That will isolate the transistors so that you can do the tests - B to C, B to E and C to E.

I would suggest getting a clear close up photo before you disconnect anything as a reference.

If the transistors are faulty, RF Parts in the US has them, probably not the cheapest, but guaranteed quality.