John,
You are not alone in this trip. Another member of this list tells me
that he connected the power to the lock indicator pin when he received
his unit and he was eager to test it. His 74ACT240 also got cooked but
the rest of the unit continued working normally.
Well, mine seems to have the same good luck. It lits the Rb lamp, the
temperature controller takes the normal current, the oscillator sweeps
back and forth and then the unit LOCKS!. I only have missing the Lock
indicator and the PPS.
And to continue the original test, I checked the PPS this time at the
input of the buffer (74ACT240 pin 2) and it is there but very difficult
to see without a storage or digital scope, the duty cycle is too low.
Anyway the trigger light is a tell tale.
And thank you for your tip about the chip type, I have to order one and
replace it because I want the PPS and the lock indicator, and maybe some
other buffers are used inside for minor functions.
BTW, maybe the units who lack the PPS have this output damaged, because
some info list this pin as power input and it seems to be true but in
other FE-5680 variants. Who knows why FE designed so different units
with the same number.
Best Regards,
Ignacio, EB4APL
On 05/01/2012 21:10, beale wrote:
I did something similar- momentary contact of +15V supply with one of the other pins- might
have been the +5 Vin, or another signal. The 75ACdT240 became very hot. I ordered a
replacement 75ACT240 part, swapped it in, and the unit seems to work fine now. Note this is
the 0.3" wide device, DigiKey p/n 74ACT240SC-ND. Confusingly, that part in 20-pin SOIC
is made in two different body widths: 0.209" / 5.3 mm and 0.295" / 7.5 mm.
This photo shows the board with the smoked chip removed (U503 at upper left),
before I installed the replacement
https://picasaweb.google.com/lh/photo/mF9WSGlEQjA8MqHhbPOJRdMTjNZETYmyPJy0liipFm0?feat=directlink
-john
-------Original Message-------
From: EB4APL<eb4...@cembreros.jazztel.es>
To: time-nuts@febo.com
Subject: Re: [time-nuts] FE-5680A performance
Sent: 05 Jan '12 11:37
I found it, I used the +15 V of my triple output supply to power the
pin 4, +5 V input. A 75ACT240 popped up and who knows the health of the
other things.
Wish me luck,
Ignacio, EB4APL
El 05/01/2012 18:54, EB4APL wrote:
>
> I agree, I've seen it in a Tek 7623A with the storage on, it is quite
> difficult without it.
>
> Regards,
> Ignacio, EB4APL
>
> PD. Just trying to verify this I made some error and let the magic
> smoke leave the unit. It is still smelling ...
>
>
>
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