Repair of a Yaesu FT100 HF/VHF/UHF Transceiver

[xrunner]

A ham friend asked me to look at this rig. It has no output power on any of it's bands. After some research I found the following known issue -

the high IC ALC problem which resulted in no TX output power in the
radio. A few of use sent our radios to the same place here in the USA...
and this place replaced the same 6 smd resistors to fix the radio.

The 6 smd resistors that were replaced were...

R3034 & R3035 - 5.6K ohm
R3038, R3040, R3041, & R3042 - 6.8K ohm

All 6 of these are located on the bottom of the PA Unit.

https://beta.groups.yahoo.com/neo/groups/FT100/conversations/topics/36891

As you can see in the attachments, we see the true output power is about 0 dBm - there is a 40 dB attenuator inline to protect my spectrum analyzer in case it decides to work. The output power at this time should be +50 (100W). Frequency is off too.

Also, we can see the ALC indication is hard full scale, which is consistent with the known issue described in the research. So, we will see if I can repair it, I have no idea if it really has the same issue or not, but it looks promising. Will have to pull the PA board out next because the SMD resistors are on the bottom. 

Oh, by the way, how about that microphone! 

[Z80]

Be careful hooking the tx to your spectrum analyser, unless the attenuator is rated to handle 100W lots of swearing will follow should it suddenly spring to life.  A dummy load & power meter / scope is safer to see if the output is working.  That will also protect you output transistors as you seem to have an ALC fault.

[xrunner]

Be careful hooking the tx to your spectrum analyser, unless the attenuator is rated to handle 100W ...

Yea, it's rated for 100W - I know what I'm doing.  Also, I want to see any small output emissions from the radio over the large bandwidth it covers so a spectrum analyzer is the tool to use. That's why I obtained that attenuator.

[xrunner]

Getting ready to pull the PA board. The SMD's in question are on the bottom. The schematic shows them, indeed as 0.1% resistors, just for this one circuit. If they have drifted will have to order from Mouser I suppose, none on hand here.

[xrunner]

Found the problem. R3042 (6.8k) was totally open. I replaced it with an 0805 I had (which is not 0.1%) and it started working. I will now order all the resistors in that area and replace them with new 0.1% resistors since these are all part of a known issue.

Also going to go through the alignment and do a complete clean-up of the radio.

[Z80]

Yes that attenuator looks the part   Nice job with the fix, did you find out what happened to the resistor?  Was it cracked?

[xrunner]

Yes that attenuator looks the part   Nice job with the fix, did you find out what happened to the resistor?  Was it cracked?

Did not see any physical issues with it, it was just open. I just ordered all the resistors needed to make sure this issue does not appear again. Meanwhile, I'm going through the service alignments till the parts show up.

[xrunner]

Proceeding with alignment. Ran into a problem yesterday in that the procedure in the service manual for the HF idling current is just wrong, but you don't find out it can't be done the way it states until after you turn some pots, then you are screwed. But, fortunately I found some great info that allowed me to get past it. Here's what One person said -

Do not trust the service manual. Its junk. I have serviced the 100D thrice -
first for a blown driver 2SC2714, then changed controller card after a
lightning strike and lastly replaced a blown pair of MRF-255 with an
unmatched pair purchased from Singapore.

...

Hope this helps you and others. Finally I would like to point out the sheer
callousness of Yaesu in designing the 100D and charging a lot of money for
a service manual that is absolute trash.

http://comments.gmane.org/gmane.recreation.radio.hardware.yaesu.ft100/14148

So, I'm proceeding with the alignments and my SMD parts should arrive today.

[xrunner]

Got the SMD resistor parts and installed them. Also applied fresh heat sink compound since the original was dry dust. Now will put the board back and finish the service alignments.

[xrunner]

Well, I found more errors in the service manual. 

On page 10 it has you inject a 1 kHz tone into the Mic line - levels of 1.5 mV, 3.0 mV, and 7.5 mV rms - to make some adjustments, however, these levels simply do not cause the stimulus desired. As the original settings are not far from other documented settings for this particular radio, I realized - oopsie - some technical writer put in a decimal place where it needn't be. The correct values are 15, 30, and 75 mV rms, which cause the correct response. Very sloppy Yaesu, very sloppy ... 

[xrunner]

Now disassembling control head and mic. Plastic parts (that can) go into ultrasonic cleaner. Mic will receive brand new cord off Ebay. Other than that these parts are OK.

[Radio Tech]

Good job on bringing this one back to life.

[xrunner]

Good job on bringing this one back to life.

Thanks. As far as I can tell now I only need three more parts - the memory backup battery, a new speaker, and the replacement mic cord. Speaker is torn and in bad shape. Sourced a new one with the same mechanical dimensions on Mouser, also the CR2025 battery with solder tabs. Should be here in a few days. Owner is pretty excited. 

[xrunner]

Prepping for backup battery replacement. According to the manual it's supposed to lose the user memories but not the service alignment memories when the battery is removed. My philosophy is - why take any chances?  Let's tack on a temporary battery.

[xrunner]

Now fighting one last problem that started cropping up. It's another known issue - high SWR indication on the front panel when there is no such actual condition. It shuts down the transmitter, and on this radio it's happening on the UHF band. You can put a dummy load right on the radio's pigtail coax and it happens. So, I'm studying the way the problem was cured when people back in the day sent it back to Yaesu to get fixed. 

[Z80]

Don't you just hate it when that happens, you're ready to bolt the lid back on and up pops another problem.  Is that an early FT100?  I seem to remember the early ones were a bit flakey and Yaesu brought out a revised version which was much more stable.  I know what you mean with the service manuals, they are obviously as bad as the old ones then.  The service manual for my FT767 has a great section on aligning the IF board, unfortunately it is completely different to the one fitted to the radio.  Oh well 

[xrunner]

Don't you just hate it when that happens, you're ready to bolt the lid back on and up pops another problem.  Is that an early FT100?  I seem to remember the early ones were a bit flakey and Yaesu brought out a revised version which was much more stable.

Appears it's an early one, because it doesn't have added cures for the high SWR issue. I have made progress however. I added a copper braid as seen in pictures people made of the mods that Yaesu added when people sent in their radios to get fixed. See here -

http://k0lee.com/ft100/Newmods.htm

As of this morning high UHF SWR only happens when the radio is first turned on for a few minutes and then doesn't appear again. I have a few more things to add but it's 90% better now.

I know what you mean with the service manuals, they are obviously as bad as the old ones then.  The service manual for my FT767 has a great section on aligning the IF board, unfortunately it is completely different to the one fitted to the radio.  Oh well 

It sucks when you follow a step, and it is wrong.  Go to this pot and adjust it until X is this value. Yea when you do that and nothing happens, you not only have no idea what they mean - the pot is now mis-adjusted and you have no idea how to correct it. I suppose you could mark a spot before you make a change, but sometimes even the slightest touch can mis-adjust something and that spot might not be exact enough to get it back. Fortunately there are people out there who document this stuff for the rest of us. 

[xrunner]

Aha! I just found this smoked ceramic cap! Guess where - on the output of the VHF/UHF PA transistor.

It's supposed to be a 39 pF 500V cap but it tests as 0.2 ohms ... it's a wonder the thing is transmitting at all. 

Edit: Added better pic and schematic snip for anyone else that may need to repair this radio.

[xrunner]

I subbed out the bad 39 pF cap with a 33 pF ceramic I had on hand and now the SWR issue is totally gone. 

The cap I used from my junk bin is not, however, rated at 500V, prolly only like 50V. I ordered the correct cap; but in the meantime the radio now appears to be functioning well. I plan on using it for the next few days until the last parts come in. Then I'll call my "customer" and he'll come and get it.

[brobers]

That microphone cord is typical for Yaesu. I have a couple of FT-1500s and a FT-100D that have all slowly fell apart like this.

[xrunner]

That microphone cord is typical for Yaesu. I have a couple of FT-1500s and a FT-100D that have all slowly fell apart like this.

It turned out to be useful while I was going through the service alignment because it allowed me to easily get to some of the wires and inject signals. Which reminded me I needed a way to easily do this again. Therefore ... I found this on Ebay and ordered one. As you can see it allows an in-out mic connection and also access to all six wires easily.



By the way, the owner of the FT-100 came over yesterday and I gave him a full demo, he was very pleased. Before he came over, last week I had also made a few JT65 contacts with it just to check it out and it succeed. However, it remains that this radio was not well designed and so the inherent issues with it remain (hot as a firecracker just receiving, bad output PA design). No telling how long it will go without other problems cropping up.

[Hayden Perrine]

Assuming you completed the repairs on the FT-100, I have 2 units, 1 won't transmit on HF, the other only puts out about 10 watts on HF.
Would you consider looking at these, as I'm more suited as an end-user.
I have been using these radios for a decade or more and have got quite used to pushing buttons and turning dials while driving therefore I have over a hundred DX contacts through this radio and would prefer getting them fixed instead of changing to a different model.

[xrunner]

I will answer you in your PM.

[m3vuv]

I realy dont know why people buy yaesu stuff,in my opinion its underbuilt over rated junk!!,every thing designed by bean counters not engineers,ive had a few yaesu radios before i knew any better!!.

[Wirehead]

I realy dont know why people buy yaesu stuff,in my opinion its underbuilt over rated junk!!,every thing designed by bean counters not engineers,ive had a few yaesu radios before i knew any better!!.

A few bad apples.. just like any other brand  I have a FT-450AT; and modified it with a RX out for SDR purposes (HupRF high impedance buffer). Built like a tank. I can run 100W CW with a brick on the key for hours. Built like a tank.