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Evening folks


Right bear with me .

I have my trusty old 857D i have also gained an FC 757at the tuner works well
when used manually has anyone ever tried to connect one to an 857d i see the
the cat port in Linear mode the radio has the four band ouputs A B C D in
tuner mode it only has band output on 1 pin a varying voltage has anyone ever
tried using this tuner with an 857d fully automatically

I also have the ft757gx as well but it needs all the caps and diodes changing
pity but such is life

Thanks Pete G6NJR

If it works in manual mode I would use that.
I don't think you can interface the two together.

It is easy to blow the circuit in the FT857D when interfacing to the wrong
tuner.

Roger KC7OM

Yep I blew mine trying it with a different tuner

Mick, SA4MDN

Hi. New member here.

I'm using my FT-857D with a MFJ-939 auto tuner. It had been working great since Nov 2019 but yesterday I had a problem where it wasn't tuning.

I'm trying to diagnose the problem. The MFJ-939 is not powering on. It normally gets power from the 857 via the interface cable. It also has an alternate power input. If I supply power to the alternate input, the tuner powers on. However,

Even with the tuner powered on, the 857 screen does not display TUNE. Pressing the TUNE soft button doesn't do anything. I tried doing a complete reset of the 857 (Press HOME and Power On), reset Menu 020 to TUNER and Menu 085 to TUNER. No success.

The MFJ-939 came with the interface cable and it's manual provides the pin out for the tuner side. It indicates that the rig is suppose to supple the 13.8vdc on three of the pins. I'm measuring 5.04vdc.?

This is a mobile install. Yesterday, when I was using the setup, it was near zero degrees F.?

I'm worried that the MFJ has killed some portion of the FT-857D. The fact that I don't see the 13.8vdc seems BAD. And that the rig doesn't seem to know the MFJ-939 is there even when the tuner is ON via alternate power make me wonder if the CAT control is killed too. I don't have a means of testing the CAT independently.

Any advise or suggestions?

Mike / KA4CDN

Which tuner and how was it blown?

Mike / KA4CDN

Maybe this, it shows 897D, but 857D is the same, its what I had to do to my 857D when I popped the cat power fuse when I connected to a wrong tuner.
Also makes changing the fuse if ever needed in the future a breeze.



Mick SA4MDN

There is a fuse in the circuit that should be checked. F1001 is the number 3.15 amp. This is a chip fuse near the CAT connector.
This should tie into the 13.8 supply.?
I have no good idea why you are measuring 5.04 unless it is being fed back from the MFJ - 939Y. Have you checked the voltage at the connector on the radio?

https://cdn.shopify.com/s/files/1/0289/7782/3843/files/MFJ-939_Schematic.pdf?v=1586534091

Thanks everyone.

I'll open the 857 later today. Can the fuse be check in circuit?

I'm thinking that I might have a more serious problem because as I mentioned, even supplying the 13.8 to the tuner via its alternate power jack, the radio doesn't indicate that the tuner is there.

I've got a buddy with a FT-857 and I plan on going over there Tuesday to do some simple swap testing so will know more than. With that info, I may call Yaesu and get their advice.

I'll report back.

Mike

I used the smaller spade type fuse when I done mine, was a better fit in the 857 case.

Mick SA4MDN

I measured the voltage on the CAT port rig at the rig's pinout. Under 1v. \

I found the schematic in the file section. File?ft857 technical supplement, part one, page 25, layout A, section A3 has part F1001 located.




Measuring continuity in circuit, it is OPEN.

So I believe you all are right on. Now to summon up the courage along with steady hands and younger eyes!?

Mike / KA4CDN

Mick and others,

One additional question. I seem to remember that fuses are not only rated for current and voltage but also speed. There are fast fuses and slow fuses. I'm guessing the SMD one in the rig is a fast one. I'm wondering if an automotive blade style fuse is 'fast enough'. Any thoughts?

Mike / KA4CDN

The speed of the fuse may be critical to the second fuse. The second fuse? Yes, the printed circuit!

Exactly. I'm trying to find something 'fast'. Some of the numbers, when I can find them, are terrible. For reference, is this fast acting?!?

Or these blade style!??

Here is the datasheet for the original F1001 SMD fuse:



I have to admit, I do not understand the?fusing time chart? It doesn't make sense to me.?

Why would you want a 3.15A fuse to blow at 3.15A? You should of course be able to run 3.15A all day. That's the purpose of the rating.

Yes, you are correct Henrik. I updated my reply after I considered the situation a bit more. I have now jumpered the SMD with a 3 amp auto blade fuse and initial testing looks good. I'll reinstall and further test tomorrow.

I'm happy to report the FT-857D is back on the air and working properly along with the MFJ-939 ATU.

I'm still at a loss to explain why the fuse opened which is worrisome. I also don't understand why the blown SMD fuse keeps CAT from working. Looking at the schematic that fuse seems to only be for the 13.8 power out.

I am grateful to everyone that offered suggestions.

Sincerely,

Mike / KA4CDN

I blew mine when I tried an 817 tuner on it, playing around while waiting for the proper tuner to arrive, have heard it can also be blown by pulling out the usb cable if using RT Systems software or other when powered up,

Mick SA4MDN