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Old 09-25-2019, 09:09 AM   #1
llonen
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Default Yaesu FT726R Transceiver

So this came into the workshop recently for repair, sadly as per the norm I don't have pics of the current state of the ongoing repair, if I remember to when next working on this I might take some only due to the wide extent of the damage. Customer report not working no transmit no audio, bench report no audio (speaker disconnected ?) transmit sometimes, receive mostly but anything up-to 500kc off frequency random.

Further findings were either full output power and or little to no output power, VFO unit PB-2445 not setting up as per service manual specifications. I had a source of one of these boards so a drop in replacement solved some of the transmit problems and put the receive back on frequency.

Remaining problems of note, random low power output in the order of a few 100 mili-watts, found the drive ALC line to the RF modules was not as per service manual setup. Reluctant to make transceiver alignment adjustments to a radio that was very unstable I lifted a few of the electrolytic's for inspection some measured bad ESR but what suprised me most was the extent of the leakage onto the PCB. Removal of these SH%^y caps around 30 of them, deep cleaning the board and replacement with decent branded caps has brought about and good return to service of the board and radio.

Now although the radio now works I am going to have to go through the remaining 5 boards and potentially replace the caps there as well.
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Old 09-25-2019, 07:00 PM   #2
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Default Re: Yaesu FT726R Transceiver

what caps did it use?
most old japanese stuff uses rubycon
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Old 09-25-2019, 07:54 PM   #3
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Default Re: Yaesu FT726R Transceiver

That radio is very well known for the RX-TX relay going bad (sometimes it receives, other times not). Also if one replaced that brick in the 2m module with a new one (it's not exactly the same as the old brick), then you get the ALC problem where you have to turn up the mic gain all the way and I think you are still going to be short a few watts.

Last edited by CapLeaker; 09-25-2019 at 07:56 PM..
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Old 09-25-2019, 08:53 PM   #4
llonen
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Default Re: Yaesu FT726R Transceiver

I am not sure what the caps were since I replaced the lot on the TX board and they went in the bin, I have a number of boards left to investigate so will let you know along with some pictures if I remember. The presenting problems were such that it was immediately clear the modules were not the specific cause, they are asymptomatic at preset. It was immediately clear from the assessment that the pair of relays on this board had been replaced or removed and re-installed at some point due to the cruddy soldering.

Will keep you updated.
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Old 09-26-2019, 04:29 AM   #5
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Default Re: Yaesu FT726R Transceiver

So I fished some of the detritus from the bin, other than Elna which I would not know much about other than they still seem to be available, the rest of them appear to be unbranded crud.

See below, sorry if the pictures don't do justice to the PCB destroying sh&* that had leaked from them. If I remember to, will see to it that some pictures of the rest of the repair in progress are uploaded.

For your viewing pleasure then oh and excuse the adjustments circularisation of said devices, they were not the easiest of things to grip with needle pliers, and no they were not torn from the PCB.

Attached Images
File Type: jpg IMG_3555.jpg (388.0 KB, 9 views)
File Type: jpg IMG_3556.jpg (375.3 KB, 9 views)

Last edited by llonen; 09-26-2019 at 04:32 AM..
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Old 09-26-2019, 10:16 AM   #6
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Default Re: Yaesu FT726R Transceiver

elna are good for general use,
i see the small ones have a mitsubishi logo on them!
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Old 10-02-2019, 05:08 PM   #7
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Default Re: Yaesu FT726R Transceiver

Well radio is all reassembled and back to the customer, in all 70 plus bad and or failing capacitors were replaced, I never really got down to what was wrong with the VFO (PB-2445) and since the board was replaced it is somewhat academic anyway. Most likely it would be some borderline capacitor but I no longer have the radio to follow this up with, another happy outcome.
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Old 10-02-2019, 08:41 PM   #8
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Default Re: Yaesu FT726R Transceiver

my guess is that the VFO was jumpy?
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Old 10-03-2019, 03:23 AM   #9
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Default Re: Yaesu FT726R Transceiver

The VFO problem was one of many, it was very jumpy or unstable and would not always lock, furthermore it would not setup as per service manual alignment. I did find that changing the dial frequency would sometimes get it to lock but it was often off frequency in excess of 500kc on receive while inhibiting the transmit. Given the board was causing problems with service manual alignment checks it seemed a likely candidate and since I have access to a known good board at an economic cost that was where the repair was started.

I did get around to replacing the few electrolytic's but since the radio was working with the replacement VFO board and the remaining alignment checks carried out as per service manual I had little incentive in potentially replacing a known good VFO with one that although the electrolytic s had been replaced and solder joints checked was still suspect bad.

Last edited by llonen; 10-03-2019 at 03:32 AM..
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Old 10-05-2019, 02:33 PM   #10
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Default Re: Yaesu FT726R Transceiver

That's what I thought, as I dealt with an 726r before. Heck, that reminds me, I need a donor PLL board for an old IC-751.
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Old 10-05-2019, 03:58 PM   #11
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Default Re: Yaesu FT726R Transceiver

While I don't have much in the way of IC-751 donor parts, what appears to be wrong with you PLL board ?
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Old 10-05-2019, 06:18 PM   #12
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Default Re: Yaesu FT726R Transceiver

got a weird problem I never seen before. The VFO works like a charm as it should and count's properly, but the VCO is weird. The vco works fine for the first 9.999khz, then it repeats the same signals in that 10khz window to every 10khz window to the full 100khz. Then the whole thing repeats with what ever I heard in the first 10khz window on the next 100khz, every 10khz to the next 100khz.
Are you still with me? lol
For example lets take 7.000.0 Mhz. I hear signals as it supposed to be from 7.000.0 to 7.009.9 Mhz. Then I hear the same thing again on 7.010.0 to 7.019.9 Mhz. Then its doing the whole smear over and over until 7.100.0 Mhz. Finally I hear new signals on 7.100.0 until 7.109.9 Mhz. So it repeats again the same signals every 10khz, until the next 100khz to 7.200.0 Mhz. It does this on all bands.
Makes my head spin reading my own crap.
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Old 10-05-2019, 08:39 PM   #13
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Default Re: Yaesu FT726R Transceiver

In many respects that is partly how this PB-2445 unit was behaving, while the display worked flawlessly for which ever band option was selected most of the time it would not provide a lock for the transmitter but when it did often it would be every so many khz this was either 30 or 50 khz for 145500 (two meter) it was slightly different for 70cm and 6 meter. The receive would also smear over and repeat itself. And this was all very unstable and intermittent, given the general bad condition of the components on all boards within the radio I suspect the problem would have been solved when I replaced the remaining capacitors on the PB-2445 unit but since by now I had a fully working radio it was not my inclination to strip the unit out and replace.

I would suggest pulling some of the caps around the area and inspect for leakage and test esr etc.
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Old 10-06-2019, 04:53 AM   #14
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Default Re: Yaesu FT726R Transceiver

does it use digital control?
maybe an old 40 or 74 series chip?
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Old 10-06-2019, 07:09 AM   #15
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Default Re: Yaesu FT726R Transceiver

Quote:
Originally Posted by llonen View Post
In many respects that is partly how this PB-2445 unit was behaving, while the display worked flawlessly for which ever band option was selected most of the time it would not provide a lock for the transmitter but when it did often it would be every so many khz this was either 30 or 50 khz for 145500 (two meter) it was slightly different for 70cm and 6 meter. The receive would also smear over and repeat itself. And this was all very unstable and intermittent, given the general bad condition of the components on all boards within the radio I suspect the problem would have been solved when I replaced the remaining capacitors on the PB-2445 unit but since by now I had a fully working radio it was not my inclination to strip the unit out and replace.

I would suggest pulling some of the caps around the area and inspect for leakage and test esr etc.
your issue is different than mine. Mine has to do something where the VCO isn't counting properly. The VCO voltage should rise as you go up the band. Well, mine jumps back. There is a contraption out of 2 IC's to make the VCO rising in voltage properly and my problem is the 10khz count is bad.
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Old 10-06-2019, 07:16 AM   #16
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Default Re: Yaesu FT726R Transceiver

Quote:
Originally Posted by stj View Post
does it use digital control?
maybe an old 40 or 74 series chip?
You are correct, it is an IC that has the problem (I verified it with my Oscope), but it isn't easy like a 40 or 74 series single IC. There are 2 IC's that together make these counts happening. I can't remember out of my head the markings off the IC's. However, look at a IC-751 schematic, go to the PLL board and look at the VCO section. Not having any old IC's like that, makes it hard to repair. I did see that the PLL board off a IC-745 looks the same as the IC-751, but I haven't gone any further to see, if it actually would work.
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