FT-857D 2 meter issue

[Darryl J. Holman]

During last Monday's VHF sprint, it became apparent that my FT-857D went
somewhat deaf on 2 meters SSB and CW. Subsequent testing (using
calibrated equipment) shows that it receives fine on all bands except 2
meters.

Two meters has lost something around 14db in FM and CW. A full reset
did nothing. I'm guessing that the 2 meter front end is not working.

I pulled the top board and tested a few diodes that are in the 2 meter
front end. They seem fine.

The RF amplifier in the front end is a dual gate MOSFET, BB304CDW (spec
sheet: http://tinyurl.com/cx8hezz). I don't know how to test this _in
situ_, so I think the next step is to simply replace it.

Mouser doesn't have these in stock and they have a message, "End of
Life: Scheduled for obsolescence and will be discontinued by the
manufacturer."

So my questions are:

1. Has anyone had a similar issue of an FT-857/817/897 going deaf on 2
meters only? Are there other things I should consider?

2. Does anyone know of a good source for the BB304CDW?

3. Does Yaesu sell components like this? And if so, how long should I
expect it to take to get the part from them?

Thanks in advance for suggestions.

Darryl, WW7D

[n6...@aol.com]

07APR2013

 

Hello Darryl, et al:

 

I have actually gotten parts from Yaesu, particularly things like microphones.

 

You might call their technical people and speak with a 'live' person. This MIGHT help.

 

Seeing that the FT857D is still sold as new by AES/HRO/similar, it shoul;d seem that Yaesu would still support it.

 

I am forwarding this thread to the W6YX  & WSWSS reflectors.

 

bt73Pete, N6ZE in DM04ne today

).  I don't know how to test this _in 
situ_, so I think the next step is to simply replace it.

Mouser doesn't have these in stock and they have a message, "End of 
Life: Scheduled for obsolescence and will be discontinued by the 
manufacturer."

So my questions are:

1.  Has anyone had a similar issue of an FT-857/817/897 going deaf on 2 
meters only?  Are there other things I should consider?

2.  Does anyone know of a good source for the BB304CDW?

3.  Does Yaesu sell components like this?   And if so, how long should I 
expect it to take to get the part from them?

Thanks in advance for suggestions.

Darryl, WW7D

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[Loren Moline WA7SKT]

Darryl,

Check this out! Not exact number but should work.

http://www.ebay.com/itm/NXP-N-Ch-Dual-Gate-RF-Transistor-BF904WR-SOT-343R-25pcs-/400094914784?pt=LH_DefaultDomain_0&hash=item5d2783e8e0



Loren Moline  WA7SKT

Member: Pacific Northwest VHF Society and ARRL
Member: Hearsat Satellite Monitoring Group.  www.uhf-satcom.com
Grid: CN86bx

---

To: djho...@u.washington.edu; PNW...@googlegroups.com; v...@w6yx.stanford.edu
Subject: Re: WW7D/R: [PNWVHFS] FT-857D 2 meter issue
From: n6...@aol.com
Date: Sun, 7 Apr 2013 15:52:14 -0400

[Loren Moline WA7SKT]

Check that ..the gates are reversed...sorry!

Loren Moline  WA7SKT

Member: Pacific Northwest VHF Society and ARRL
Member: Hearsat Satellite Monitoring Group.  www.uhf-satcom.com
Grid: CN86bx

---

From: lmo...@hotmail.com
To: n6...@aol.com; djho...@u.washington.edu; pnw...@googlegroups.com; v...@w6yx.stanford.edu
Subject: RE: WW7D/R: [PNWVHFS] FT-857D 2 meter issue
Date: Sun, 7 Apr 2013 13:12:30 -0700

[Darryl J. Holman]

Hi Loren,
Thanks for the tip. I'll keep the BF904WR in mind as a last resort.
The specs look reasonably close, but perhaps the BP904WR is a bit too
fragile.

In any case, I think the pin out is identical to the BB304CDW. The
photo on Ebay shows a device with a reverse pin-out.

Best,
Darryl, WW7D

On 04/07/2013 01:16 PM, Loren Moline WA7SKT wrote:
> Check that ..the gates are reversed...sorry!
>
> Loren Moline WA7SKT
>
> Member: Pacific Northwest VHF Society and ARRL
> Member: Hearsat Satellite Monitoring Group. www.uhf-satcom.com
> Grid: CN86bx
>
>

> ------------------------------------------------------------------------

> From: lmo...@hotmail.com
> To: n6...@aol.com; djho...@u.washington.edu; pnw...@googlegroups.com;
> v...@w6yx.stanford.edu
> Subject: RE: WW7D/R: [PNWVHFS] FT-857D 2 meter issue
> Date: Sun, 7 Apr 2013 13:12:30 -0700
>
> Darryl,
>
> Check this out! Not exact number but should work.
>
> http://www.ebay.com/itm/NXP-N-Ch-Dual-Gate-RF-Transistor-BF904WR-SOT-343R-25pcs-/400094914784?pt=LH_DefaultDomain_0&hash=item5d2783e8e0
>
>
>
> Loren Moline WA7SKT
>
> Member: Pacific Northwest VHF Society and ARRL
> Member: Hearsat Satellite Monitoring Group. www.uhf-satcom.com
> Grid: CN86bx
>
>

> ------------------------------------------------------------------------

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[Edward R Cole]

Darryl,

Good advice so far. A loss of 14-dB in sensitivity does look
suspiciously like typical preamp gain in a transceiver. You indicate
it is a MOSFET. Measure dc levels on gate(s), source and drain. Is
this device used in the 6m section (make comparison
measurements). Quite often the gate is at dc ground so there should
be a small bias voltage on the source (0.5-1.5v) and something like
5v to 8v on the drain. The two diodes are probably back to back so
the resistance across them would be the same in either direction (if
not then perhaps one diode is gone). A short there would also
explain the drop in signal. Does the radio use pin-diode TR
switching? You can bridge the pin-diode in the Rx path (but do not
short out its bias voltage) and test if it is at fault.

Obtaining replacement Fets from Yaesu is a good idea so you get the
correct replacement (order two, just in case). Those of us who run
preamps have learned to squirrel away a number of spares (as
equipment often outlasts the supply of devices).

With any MOS device use static control when replacing the device. GL!

73, Ed - KL7UW
<experienced Gasfet changer>
getting a nice(?) snowfall at present

[Darryl J. Holman]

Thanks Ed,

I haven't quite figured out how to get the motherboard connected up
and powered on with the main board inverted for access, but if I don't
get fast success trying the brute force approach (replace) then I'll try
that.

A different BB304CDW is used for 160-6 meters, so I should be able
to do the comparison--thanks for that suggestion. That front-to-back
diode thing is used in the UHF front end, but not the VHF front end.

The radio does use pin-diode TR switching, so I'll look at that, as
well.

Thanks for the advice on spares...I'll order a few.

Best,
Darryl

[Dale KD7UO]

Darryl
I had the same thing happen to me, only on 6m, with my 897 (same circuit as the 857).  It was the front end transistor.  I believe the radio is somewhat sensitive to strong RF fields from nearby transmitters.  I think I blew my 6m transistor when I was using my other radio on a different band during a contest.  As was already mentioned, go to Yaesu direct by phone and they have all the parts.  And the coolest thing is the prices are almost giveaway.  You'll probably pay more for shipping than the cost of the part itself.  What you want is:

IC BB304CDW-TL, Yaesu # G1093324.  This is Q1024 which is the 2m front end.

Since the parts are so cheap and shipping is a fixed price for one or a dozen parts, I would advise you to also order the following parts at the same time:

1.  Order an extra of the above because it is also used for Q1023, 76-109MHz front end.
2.  Transistor 2SC5374-TL, Yaesu # G3353748.  This is Q3034, 50MHz preamp
3.  FET NE3509M04-T2-A, Yaesu # G3070387.  This is the 432MHz RF amp.
4.  Ceramic filter ALFYM455H=K, Yaesu # H3900542.  This is the AM Filter.

The 857 and 897 have a known problem with the AM filter; if you start getting S9 static crashes continuously all bands all modes and no antenna, your filter has broken down.  If you google it you'll see many, many folks have had this problem.  The filter is about $3 so might as well have one on hand.

I did the filter repair and the blown 50MHz transistor repair on mine.  It's the usual SMD exercise; it looks impossible at first but if you think small and plan it out it isn't particularly difficult.  I think all of the above parts together come to less than $20 if memory serves.  I bought the filter a couple of years ago and all the transistors about 6mos ago.  If you suspect anything else, just buy it.  They're cheap parts and they'll quote you the price right over the phone.  The 857 service manual is available free on-line if you haven't already downloaded a copy.  It has all the board layouts and part numbers.

Good luck
dale kd7uo

[Darryl Holman]

Hi Dale,

Thanks for the excellent (and expert!) advice. I've gotten a lot of helpful
advice from very generous people and I really appreciate it all. I've also
talked to Kenwood tech support--it was helpful. I CAN order the parts, and they
are inexpensive. But the technician feels it will take an hour of labor to fix
the radio. I am always reluctant to have someone else fix anything for me--I
feel like I lose the opportunity to learn something AND it is how I justify
buying new tools & test equipment. (Okay...I'm also a cheapskate.) But, man,
it's hard to beat getting it fixed for, perhaps, $150 (with shipping). I've
spent more than $150 of my time on the problem in the past week just
contemplating the repair. If I do send it in, I won't do so until after the
Spring Sprints (and 7QP) since it still works fine on 432 and HF. The next
time I absolutely need 2 m is for the June VHF contest.

On Sunday, I pulled the circuit board and tested the relevant diodes in the
2m receiver pathway. They were fine. At the time, I didn't know that the
aircraft band was also receiving very poorly, and that the FM broadcast receiver
works just fine. My reading of the schematic and block diagram suggests that
either I have blown two separate RF amp transistors (both BB304Cs) in the
(separate) 2m and Aircraft Band RF amplifiers, OR I have a bad diode immediately
upstream or immediately downstream of both amps. Parsimony suggests the
latter, but I thought I checked all of those diodes. Perhaps I neglected to
check the downstream diodes.

In any case, I am contemplating ordering the parts and taking a stab (a very,
very controlled stab) at fixing the rig. If so, I'll definitely take your
advice and order some additional spares for future issues, particularly the
notorious ceramic filter issue.

The SMD repair will be an interesting challenge. I'd done a bit of SMD
construction, and I have plenty of old circuit boards to practice on first.
Perhaps I should give up coffee & wait a week for the caffeine headaches to
subside before attempting the repair. :) I'll need to try before May 5th so I
still have time to send it back to Yaesu should I make a total mess of it, or
my repairs prove unsuccessful.

Best wishes,
Darryl
ww7d