[time-nuts] FE-5680A performance - replacing fried chip

EB4APL eb4apl at cembreros.jazztel.es
Thu Jan 5 20:56:32 UTC 2012


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<eb4apl at cembreros.jazztel.es>
>>   To: time-nuts at 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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