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Old 4th Oct 2018, 11:19 pm   #1
Phil G4SPZ
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Default Yaesu FT290R Mk 1 squelch fault

My venerable FT290 which I've owned from new since 1983 has developed an odd fault on receive in FM mode only. When switched on from cold, it works fine for half a minute or so, but then the squelch opens and rotating the squelch control clockwise has no effect. The RF side is working as incoming FM signals are received. The receiver works fine on SSB and CW, and the transmit side works perfectly on all modes.

The user handbook contains a legible circuit diagram, but I have been unable to find a proper service manual anywhere.

Probing around the circuit when the fault is present has revealed that the supply voltage at pin 4 of the MC3357P FM demodulator IC is low at 2.5 volts, and varying slightly. This should be nearer 6 volts, derived from the FMR 6.8 volt supply line. Pin 4 is decoupled by R116, 220 ohms in series, and C104, a 10uF electrolytic, to chassis. C104 is at the moment my prime suspect.

The problem is, this circuit board is so tiny that without a component placement diagram I can't identify C104, let alone replace it! It's also proving impossible to identify any of the connections to the board.

Does anyone have a service manual, please?
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Old 5th Oct 2018, 4:55 am   #2
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Default Re: Yaesu FT290R Mk 1 squelch fault

As far as I know what you get in the instructions that came with the radio are it as far as a service manual goes. Good luck with it, IMHO I think they are one of the worst radios ever made, typical Yaesu rubbish!

G.
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Old 5th Oct 2018, 7:42 am   #3
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Default Re: Yaesu FT290R Mk 1 squelch fault

Maybe try asking on the FT290 user group.

https://groups.yahoo.com/neo/groups/...bag/info?tab=s

There is also as circuit diagram on the link below.

http://www.nlwarc.co.uk/wp-content/u...FT290R_sch.pdf

The user manual can also be found easily with a google search.

John
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Old 5th Oct 2018, 8:34 am   #4
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Default Re: Yaesu FT290R Mk 1 squelch fault

Thanks John. I've joined that group and hope someone there can assist. Oddly, the service manual is freely available on the internet for the Mk 2 but not for the Mk 1.
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Old 5th Oct 2018, 10:15 am   #5
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Default Re: Yaesu FT290R Mk 1 squelch fault

I don't know the specifics of this circuit (My FT290 is a MKII) but the MC3357 was very commonly used in FM-only CB radios in the early eighties and I remember the FM squelch is one of the built-in functions of that IC.

If you happen to have a spare MC3357, maybe try dropping one in? Assuming it's a DIP version and not SM, of course.
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Old 5th Oct 2018, 10:31 am   #6
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Default Re: Yaesu FT290R Mk 1 squelch fault

Just a thought regarding the lov voltage you have on the chip. I had an issue with one of the mk1 models years ago, as soon as the volume was increased the audio was garbled, I only had about 5 volts at the audio amp IC when it should of been 12V. There was a 1/4 watt resistor in the supply wire to the amp IC, it crumbled to dust! Think I replaced it with a 470 ohm half watt job, that cured it, why power something with such an under spec device? One of the reasons I dislike Yaesu stuff, everything is just on the margins of being man enough for the job, bean counters I expect May be worth a look where the IC gets its feed from. This radio was owned from new and wasn't modified, that's how Yaesu made it!

73 Paul M3VUV.

Last edited by Station X; 8th Oct 2018 at 11:12 pm.
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Old 5th Oct 2018, 10:46 am   #7
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Default Re: Yaesu FT290R Mk 1 squelch fault

Thanks all. I reckon the chip's OK. The nature of the fault and its onset leads me to accuse C104 - I've had a number of similar faults caused by shorted decoupling electrolytics on a variety of devices - but I'll obviously check R116 as well.

I've posted a message on the Yahoo group asking for a component layout.
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Old 5th Oct 2018, 5:01 pm   #8
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Default Re: Yaesu FT290R Mk 1 squelch fault

Over the years I have had some odd faults with IF strips using the 3357 and 3359. It may be worth checking the resistance of the rather high value squelch bias resistor if you can find it. I think they are usually about 820K ish. The IF strips using these chips can be temperamental but the fact that the supply is low has got to be your first line of investigation. This could alter the squelch bias setting point and cause problems. The usual law of the likely hood of the component being faulty is inversely proportional to the number of legs it has rules here. I am normally reluctant to change chips because of this. Leaky electrolytics etc?
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Old 5th Oct 2018, 6:21 pm   #9
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Default Re: Yaesu FT290R Mk 1 squelch fault

Yes I'm fairly sure that C104 is the culprit, as I said right at the beginning in post #1. The problem is spotting C104 on the crowded board! Why is it proving so difficult to find a layout diagram for such a ubiquitous transceiver?
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Old 5th Oct 2018, 7:53 pm   #10
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Default Re: Yaesu FT290R Mk 1 squelch fault

The only major change made to FT290R1 in the UK was to fit the Mutek front end pcb.
The 290R2 is a totally different radio.

Is this your set ?
http://www.foxtango.org/ft-library/F..._schematic.pdf
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Old 5th Oct 2018, 8:18 pm   #11
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Default Re: Yaesu FT290R Mk 1 squelch fault

Yes indeed, that's my set, but all that information is contained in the User Manual which I already have. Perhaps Yaesu never made a proper Service Manual available for the Mk 1, as they did for the Mk 2?

I think I am going to have to resort to forensic examination of the board from both sides.
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Old 5th Oct 2018, 8:51 pm   #12
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Default Re: Yaesu FT290R Mk 1 squelch fault

I haven't trawled through the lists, but maybe there could be something at either of these two links, and possibly other useful info:

'Mods, information and glitch fixes for the Yaesu FT-290 MK I':

http://www.whelan.me.uk/radio/mods290i.htm

'Modifications for the Yaesu FT-290':

http://www.radiomods.co.nz/yaesu/yaesuft290.html

The guy who'd know the answer would be Harold Leeming, but he retired some years ago, thought wrote (maybe still does) a column in P.W.

The circuit and PCB looks a bit of a nightmare, so I do hope you manage to home in on the problem and fix it Phil.

Can't grumble at 35 years of ownership from new I guess!
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Old 5th Oct 2018, 11:12 pm   #13
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Default Re: Yaesu FT290R Mk 1 squelch fault

Quote:
Originally Posted by Phil G4SPZ View Post
Perhaps Yaesu never made a proper Service Manual available for the Mk 1
I don't actually know if that is true but when you are searching it might help you to know that Yaesu often labelled such information the 'Technical Supplement' rather than the 'Service Manual'.

You might want to include that in your search terms.
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Old 5th Oct 2018, 11:38 pm   #14
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Default Re: Yaesu FT290R Mk 1 squelch fault

Thank you to David and SH for those helpful suggestion. I tried the links in David's post but unfortunately they only lead to the ordinary User Manual. Good point about Harold Leeming, though; yes, I remember reading his articles and I'll follow that up. The circuit looks a nightmare, agreed, but like most circuits it can be broken down into bite-sized chunks. The hard bit is the PCB itself, which is so jam-packed with components and covered with spaghetti wiring that it's proving very difficult to locate the particular capacitor. There are few if any component references printed on the board, and the components are so close together that I can't see the values printed on them. The only saving grace is that nothing is surface mounted!

I have just tried searching for 'Technical Supplement' but sadly it returns nothing more than the User Manual (or re-hashed scans therefrom containing no additional information).

I have e-mailed a major UK Yaesu importer in the hope that they may be able to help.

I agree that 35 years is not a bad age for anything electronic, but most of the sets I repair are eighty years old! This fault is simply the 1980s equivalent of the 1930s leaky waxie decoupler, albeit shrunk in size rather dramatically...
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Last edited by Phil G4SPZ; 5th Oct 2018 at 11:42 pm. Reason: Afterthought
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Old 5th Oct 2018, 11:57 pm   #15
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Default Re: Yaesu FT290R Mk 1 squelch fault

Sorry about that: I remembered I had the service manual - sorry, technical supplement, for my FT-290R2 as a PDF on a CD somewhere and went hunting for it on the off chance that the CD (which I bought, years ago) might also cover the MK1: Unfortunately it does not.

The Technical Supplement for the R2 version is exactly the sort of manual you are trying to find for the Mk1: Comprehensive, with nice PCB layout diagrams. Seems odd that they would not have produced a manual of similar quality for the original 290.

You could also broaden your search to service information for the FT690 (6 metre version) and the FT790 (70cms version) because the odds are the FM RX IF section is virtually identical, probably even down to the layout being identical in that area. That said, surely the 2m version should be the most widespread and easy to find.
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Old 6th Oct 2018, 12:18 am   #16
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Default Re: Yaesu FT290R Mk 1 squelch fault

Good point! That's worth a try too.

I am literally just playing with this radio now and monitoring the DC voltage on pin 4. From cold it starts at about 6.5 volts and everything works perfectly, then the voltage falls erratically and the squelch opens exactly in sync with the falling voltage. Occasionally the voltage shoots back up for a few moments and all works normally for a while. So I think I'm on the right track.

There are several small 10uF caps in the vicinity of the MC3357. If I can get access to the print side of the PCB, I should be able to work out which is C104 and replace it, but it's going to be a tricky job.
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Old 6th Oct 2018, 12:28 am   #17
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Default Re: Yaesu FT290R Mk 1 squelch fault

A spot of freezer spray with a narrow nozzle tube on it would probably help if you have some handy.
Alan.
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Old 6th Oct 2018, 9:23 am   #18
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Default Re: Yaesu FT290R Mk 1 squelch fault

Or, if you don't have freezer spray put the set in the fridge (not freezer!) for half an hour or so, and then take it out and see if you can accelerate the onset of the fault by holding the tip of a soldering iron very close to each suspect capacitor.

I suppose the bottom line is that you are eventually going to have to access the print side of the PCB to effect a repair no matter which component it turns out to be, so you may as well bite the bullet and do that sooner rather than later, after which it should be a simple matter to see which of those capacitors has its + lead connected to the MC3357 pin 4 by a copper trace. And to be honest, if it comes down to a choice of 2 or 3 10uF capacitors, for what they cost, just change them all - they will all be the same age and made by the same manufacturer.

I notice there is currently a 290R MK1 PCB (only) for sale in one of the usual places, the accompanying images are good quality and show both sides of the PCB so you might be able to make use of the print / track side image to follow the tracks away from the MC3357 pin4 to see which capacitor is your likely suspect.
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Old 6th Oct 2018, 10:11 am   #19
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Default Re: Yaesu FT290R Mk 1 squelch fault

Thanks for that. I'd come to much the same conclusion that, from the print side, locating the suspect cap should be possible. Basically I'm looking for the cap with the varying DC potential on its + lead the same as pin 4 of the I.C. As you say, I need to bite the bullet! Getting the battery compartment out is the next step.

Thanks for the tip about the PCB on sale, too, very useful.
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Last edited by Phil G4SPZ; 6th Oct 2018 at 10:12 am. Reason: Addendum
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Old 6th Oct 2018, 10:23 am   #20
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Default Re: Yaesu FT290R Mk 1 squelch fault

Generating a mirror image of the component side photo in software and printing or viewing that alongside the track side helps overlay components onto the tracks 'looking through' the board. May be worth a go Phil?
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