Repair of a Yaesu FT100 HF/VHF/UHF Transceiver - Page 1
Forum section: electronics / rf-microwave

author: xrunner
author_rank: Super Contributor
timestamp: February 20, 2017, 11:30:32 pm
content: 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 -QuoteAs 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!

author: Unknown
author_rank: Unknown
timestamp: February 21, 2017, 12:33:01 pm
content: 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.

author: xrunner
author_rank: Super Contributor
timestamp: February 21, 2017, 12:54:08 pm
content: Quote from: Z80 on February 21, 2017, 12:33:01 pmYea, 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.

author: xrunner
author_rank: Super Contributor
timestamp: February 21, 2017, 01:06:52 pm
content: 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.

author: xrunner
author_rank: Super Contributor
timestamp: February 21, 2017, 11:23:53 pm
content: 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.

author: Unknown
author_rank: Unknown
timestamp: February 22, 2017, 11:50:57 am
content: Yes that attenuator looks the partNice job with the fix, did you find out what happened to the resistor? Was it cracked?

author: xrunner
author_rank: Super Contributor
timestamp: February 22, 2017, 04:47:09 pm
content: Quote from: Z80 on February 22, 2017, 11:50:57 amDid 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.

author: xrunner
author_rank: Super Contributor
timestamp: February 23, 2017, 03:52:50 pm
content: 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 -QuoteSo, I'm proceeding with the alignments and my SMD parts should arrive today.

author: xrunner
author_rank: Super Contributor
timestamp: February 24, 2017, 01:24:08 pm
content: 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.

author: xrunner
author_rank: Super Contributor
timestamp: February 25, 2017, 01:04:07 am
content: 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 ...

author: xrunner
author_rank: Super Contributor
timestamp: February 26, 2017, 02:33:24 pm
content: 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.

author: Radio Tech
author_rank: Frequent Contributor
timestamp: February 27, 2017, 02:20:30 am
content: Good job on bringing this one back to life.

author: xrunner
author_rank: Super Contributor
timestamp: February 27, 2017, 01:08:06 pm
content: Quote from: Radio Tech on February 27, 2017, 02:20:30 amThanks. 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.

author: xrunner
author_rank: Super Contributor
timestamp: February 27, 2017, 11:01:32 pm
content: 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.

author: xrunner
author_rank: Super Contributor
timestamp: March 01, 2017, 03:23:42 pm
content: 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.

author: Unknown
author_rank: Unknown
timestamp: March 01, 2017, 05:11:43 pm
content: 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

author: xrunner
author_rank: Super Contributor
timestamp: March 02, 2017, 01:02:01 pm
content: Quote from: Z80 on March 01, 2017, 05:11:43 pmAppears 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.htmAs 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.QuoteIt 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.

author: xrunner
author_rank: Super Contributor
timestamp: March 02, 2017, 03:40:19 pm
content: 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.

author: xrunner
author_rank: Super Contributor
timestamp: March 04, 2017, 02:17:42 am
content: 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.

author: brobers
author_rank: Newbie
timestamp: March 06, 2017, 06:28:15 am
content: 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.

author: xrunner
author_rank: Super Contributor
timestamp: March 06, 2017, 01:20:48 pm
content: Quote from: brobers on March 06, 2017, 06:28:15 amIt 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.

author: Hayden Perrine
author_rank: Newbie
timestamp: October 19, 2018, 05:17:29 pm
content: 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.

author: xrunner
author_rank: Super Contributor
timestamp: October 19, 2018, 10:08:28 pm
content: I will answer you in your PM.

author: m3vuv
author_rank: Super Contributor
timestamp: October 20, 2018, 10:41:07 pm
content: 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!!.

author: Wirehead
author_rank: Regular Contributor
timestamp: October 25, 2018, 06:42:46 am
content: Quote from: m3vuv on October 20, 2018, 10:41:07 pmA few bad apples.. just like any other brandI 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.

author: mrz80
author_rank: Contributor
timestamp: December 01, 2018, 07:41:48 pm
content: Quote from: m3vuv on October 20, 2018, 10:41:07 pmMy FT-100's been giving stalwart service for many years, most of 'em mobile and portable, getting banged around and overheated. I will concede it's a right pain in the rear to work on, with everything jammed in cheek-to-jowl in such a tiny case. So long as you baby that unobtanium VHF final (I don't run 2m or 440 at more than half output just to keep it running cool) it's a fine rig. My big like is the 6m and VHF receivers are worlds ahead of the newer 857/897, and the Icom 706-of-whatever-generation.Quote from: Wirehead on October 25, 2018, 06:42:46 amJust remember to use a dummy load instead of an antenna for that torture test, or you might get a nastygram from th' FCC!

author: gi4ohh
author_rank: Newbie
timestamp: February 23, 2019, 05:07:20 pm
content: x-runner can you pm me please

author: xrunner
author_rank: Super Contributor
timestamp: February 23, 2019, 10:47:18 pm
content: Quote from: gi4ohh on February 23, 2019, 05:07:20 pmI have PMed gi4ohh and he asked me to point to the resistors on the board. I told him to go back to this thread so I can post the pics here so that it may help other people in the future.I will make the post in a bit ...

author: gi4ohh
author_rank: Newbie
timestamp: February 23, 2019, 11:12:13 pm
content: thanks

author: xrunner
author_rank: Super Contributor
timestamp: February 23, 2019, 11:48:58 pm
content: Check the schematic and the annotated circuit board, that will show you the resistors to be replaced.Good Luck!

author: gi4ohh
author_rank: Newbie
timestamp: February 24, 2019, 12:00:16 am
content: the 5.6k resistersmy readings are as follows5.6k5.4k4.28k4.36kthe6.8k resistersmy readings are as follows4.18k5.16k

author: xrunner
author_rank: Super Contributor
timestamp: February 24, 2019, 02:17:08 pm
content: Remember that measuring resistors in-circuit might not give the value on the resistor because it might be in parallel with other resistances. For example R3040 is essentially in parallel with R3035 & R3033 (and perhaps other things in other places not shown) as far as measuring it's resistance in-circuit. If you are concerned that the radio has the same problem as the one I repaired, I would just replace all of these resistors because it's not hard and the cost is so little.

author: Velund
author_rank: Regular Contributor
timestamp: February 27, 2019, 09:32:40 pm
content: Quote from: Wirehead on October 25, 2018, 06:42:46 amCannot say anything bad about cooling of FT-450, but once tried to use my 450AT in a contest (RDXC, IIRC). After hearing for the first CW pileup replaced them with my old good FT-900CAT, without that buggy DSP, that cannot handle more than 2-3 CW signals in a passband. What was a nice pileup on FT-900 appear to be a meaningless chaotic beeping on 450... BTW - no such problems on Elecraft K3.

author: gi4ohh
author_rank: Newbie
timestamp: March 14, 2019, 10:56:51 pm
content: replaced resisters now full 100 watts on hfbut on vhf uhf 1.5 watts only

author: gi4ohh
author_rank: Newbie
timestamp: March 17, 2019, 01:15:10 pm
content: SUPPOSE THE CHANCES OF GETTING A MOTOROLA SRF 7043 MOSSFET ARE SLIMHAS ANYONE TRIED A REPLACEMENT OR EQUIVALENT WOULD LIKE TO GET THIS RADIO GOING ALSO ON 2 METERS AND 70CMS

author: keystone
author_rank: Contributor
timestamp: March 21, 2019, 04:33:03 pm
content: Hi xrunner. I am putting together a test bench and looking for attenuators. Was wondering where you got that one. I'm working on an old kenwood tr-7800 fm 2 meter radio that has a problem with the squelch circuit, no squelch. I've looked at your post of the tr-740o repair. Thanks for posting that and this one too. Have you ever run into a no squelch problem with a radio like this before? Keep up the good work.

author: xrunner
author_rank: Super Contributor
timestamp: March 22, 2019, 01:20:57 am
content: Quote from: keystone on March 21, 2019, 04:33:03 pmThe 40 dB? Oh I got it from a Chinese supplier on Ebay. You can find others used too that came out of commercial equipment.QuoteWell I don't have the radio anymore because I repaired it for a friend, and have never touched one either before or since. You'll just have to do the troubleshooting on the bench and follow the schematic. I'm sure you can fix that.As far as what you asked me in the PM, concerning what test equipment to get, let's talk about it here since there are other members that can input suggestions too. You said you got a DS1045Z. That's great. Some of the items on my bench include -HP RF signal generator 100 kHz to 1 GHz100W dummy loadRigol DS1045ZRigol 30 MHz function generatorRigol Bench DMMRigol DS815 Spec. Analyzer w/tracking generator13.8V 30A power supply for testing ham gearTwo hp power supplies for low current applicationsOther selections of various inline attenuators with both SMA and N connectorsAlso a whole lot of other test equipment on the side but the above will do a lot of good for you.

author: N4wy
author_rank: Newbie
timestamp: April 03, 2019, 12:54:42 pm
content: Hello Xrunner, I have been searching for a replacement control board for the FT-100 for two years now. Either Ebay has a board listed for the price of a used FT-100 $300+ or nobody has one. This surprises me as many FT-100's are sitting around with problems. You'd think someone would be piecing them out for parts. Have you run across another source other than ebay for FT-100 parts or FT-100 for sale - not working for parts? Thanks. N4WY

author: xrunner
author_rank: Super Contributor
timestamp: April 04, 2019, 01:48:16 am
content: Quote from: N4wy on April 03, 2019, 12:54:42 pmHello.No, I'm afraid I don't know of other sources for parts. Keep looking on Ebay they're bound to turn up over time.

author: F4IUJ
author_rank: Newbie
timestamp: February 13, 2023, 03:07:16 pm
content: Hello,I have exactly the same issue, so I am going to replace the SMD resistors. So, do you know what size they are so that I can order them before dismantling the transceiver ?73,Yannig

author: xrunner
author_rank: Super Contributor
timestamp: February 13, 2023, 03:33:42 pm
content: Quote from: F4IUJ on February 13, 2023, 03:07:16 pmOne of my posts earlier noted that they were 0805 size.

author: F4IUJ
author_rank: Newbie
timestamp: February 13, 2023, 04:09:19 pm
content: Ooops,Sorry, I need some better glasses!!!Anyway, thank you for making this info public, I don't think that I would have diagnose the issue alone.