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Replacement part for IC4 #fst3253


Wes AE6ZM
 

Has anyone found a source for the SOIC footprint version of IC4, the FST3253? I have a unit on the bench with overheating of the 5v regulator, and it appears that IC4 is drawing excess current. Static measurement shows ~140 ohms VCC to ground. Everything else checks OK on the 5V bus. 
--
> I finally got it all together...now I can't remember where I put it<

VY 73,
Wes

AE6ZM

Sierra Vista, AZ

 


Alan G4ZFQ
 

and it appears that IC4 is drawing excess current. Static measurement shows ~140 ohms VCC to ground. Everything else checks OK on the 5V bus.
Wes,

Before replacing anything be completely sure.
Most faults are solder whiskers, if it was like it from the start even an unetched piece of copper, component failure is unusual except when stressed.
A test is to gently lift pin 16 with a pin.

73 Alan G4ZFQ


Steven Weber
 

If It were drawing excessive current, it would be getting very, very hot to the touch.

 

Make sure the 74AC00 is installed in the correct direction.

 

Soldering issues are by far the most common reason a kit does not function. Rarely is it a bad part, in fact it’s almost unheard of. You have to work really, really hard to damage a modern IC. Reverse supply polarity will kill a lot of ICs’ but not always. They usually survive being in the wrong way around.

 

I sure hope you don’t have to change out IC4, that will not be easy.

 

73, Steve KD1JV

 

 

>and it appears that IC4 is drawing excess current. Static

> measurement shows ~140 ohms VCC to ground. Everything else checks OK on

> the 5V bus.

 

Wes,

 

Before replacing anything be completely sure.

Most faults are solder whiskers, if it was like it from the start even

an unetched piece of copper, component failure is unusual except when

stressed.

A test is to gently lift pin 16 with a pin.

 

73 Alan G4ZFQ

 

 

 


Wes AE6ZM
 

Thanks to all for the suggestions. This unit took some kind of hit, the 74ACT00 was shorted, along with several other components damaged. I cut the 5V trace right at the last via to the VCC pin on the 3253, so it was tested completely isolated from the circuit. To quell all worries, I have been working the service bench since 1969. SMD repair is a pain, but thank goodness for magnifiers!!! If I can get a new part I will cut this old one out pin by pin.
Now what would be of greatest help is if someone has a source for the SOIC 3253. Hate have to send this unit back to the owner as a transmitter only.
--
> I finally got it all together...now I can't remember where I put it<

VY 73,
Wes

AE6ZM

Sierra Vista, AZ

 


Wes AE6ZM
 

Miracles of miracles! Thanks to Jim K8IQY who noticed Mouser is now showing a large stock of the SOIC. When I checked them earlier today they showed no stock at all for the ..MX part. I am ordering a bag. 
Thanks again to all who offered help. Great community here.
--
> I finally got it all together...now I can't remember where I put it<

VY 73,
Wes

AE6ZM

Sierra Vista, AZ

 


M0RON
 

While not related to the chip in question, components can and do fail for no reason. 
I have a QLG1 which was happily running for weeks, then I noticed that the red and green led's were permanently lit, green led should pulse, also no pulsing yellow led.
Problem was traced to the IC, there was a pulsed input but a constant output instead of pulsing. New chip ordered from a reputable supplier, fitted into a socket and GPS is now happy again. 
No reason for the failure, it just did. Maybe it was slightly out of tolerance when manufactured or poor materials. But I do agree, it is rare for good chips to fail. 
Andy.
--
The universe is made up of Protons, Neutrons, Electrons but contains only one M0RON.


Alan G4ZFQ
 

While not related to the chip in question, components can and do fail for no reason.
Andy,

I realise this particular one under discussion was damaged by some mishap.

I have a QLG1 which was happily running for weeks, Problem was traced to the IC, there was a pulsed input but a constant output instead of pulsing. New chip ordered from a reputable supplier, fitted into a socket and GPS is now happy again.
As Hans has said, can you be absolutely sure another fault was not rectified by the disturbance of the replacement? Did you test the IC after removal, or was it damaged by that unknown fault? It might just take a solder or wire remnant to short something before it drops never to be found. It sounds unlikely but much of our complex modern electronics run for years without failure.
Yes a few components do die but on the other hand I am amazed just how robust many are. ICs getting really hot due to being the wrong way round, complex SM ICs removed/replaced a number of times still working apparently normally.

73 Alan G4ZFQ


M0RON
 

Hi Alan, 
Definitely the chip. 
Qlg1 was attached to a u3s and was working fine for weeks. Then it suddenly stopped, u3s still running, 5v very well regulated supply. I initially thought it was the rf chip but I probed the input to the chip from the rf chip and it was definitely receiving signals from the rf chip, the output however was a constant 2.34v or something around there on both outputs pins 3 and 8. Consequently pins 4,5,12 and 13 were fed a constant voltage which meant that the green led was constantly on and the yellow led never lit. Removed chip without damaging the board, soldered in a socket, replacement chip and all was good again and still is.
No voltage spike or incorrect voltage applied, it just failed, must have been an internal fault,  I destroyed the chip to remove it from board so didn't check it further. Just one of those unexplained failures, though I must say that I haven't had any other IC's from anything else I've built fail so one chip isn't bad and nothing else was damaged. 
Andy
--
The universe is made up of Protons, Neutrons, Electrons but contains only one M0RON.


Wes AE6ZM
 

Some decades back when there was still a lot of equipment using vacuum tubes (valves) a common phrase heard in tech chat was "solid state`. We were aware of a phenomenon related to "SS" that we called "infant mortality", meaning that if a SS device were going to fail it would happen soon after it was put into service. The perception was that if it survived the "infant" period, it would last forever. A perception likely resulting from the reality that the vacuum tube started dying the moment you put it into sevice, and would certainly fail after a few hours of service, 'few' being relative to the life expected from these 'new fangled' SS things. Truth is, SS devices do not last forever, and as you said, internal weakness may be one of the causes. Having a lot of our equipment connected to impulse collectors (antennae) may also play havoc. In some cases it could be technician oops'es.
--
> I finally got it all together...now I can't remember where I put it<

VY 73,
Wes

AE6ZM

Sierra Vista, AZ

 


James Daldry W4JED
 

Hi, Wes

Found it on thepartsplace.k5nwa.com for 70 cents.

Jim W4JED

On 2/4/19 4:45 PM, Wes wrote:
Has anyone found a source for the SOIC footprint version of IC4, the FST3253? I have a unit on the bench with overheating of the 5v regulator, and it appears that IC4 is drawing excess current. Static measurement shows ~140 ohms VCC to ground. Everything else checks OK on the 5V bus. 
--
> I finally got it all together...now I can't remember where I put it<

VY 73,
Wes

AE6ZM

Sierra Vista, AZ

 


Wes AE6ZM
 

Pretty good price Jim, I paid 53.5 cents each, but $8 in shipping from Mouser. Course, I bought some other bits-n-bobs that were not available on the Parts Place. 

I need to get my browser bookmarks a little better organized so I don't need to rely on Google searches so much. The Parts Place did not appear during my search. And I had completely forgotten about it. This getting old stuff sure isn't for the faint-of-heart!!

> I finally got it all together...now I can't remember where I put it<

VY 73,
Wes

AE6ZM

Sierra Vista, AZ

 


Jim Kortge
 

On 2/5/2019 6:41 PM, Wes wrote:
Pretty good price Jim, I paid 53.5 cents each, but $8 in shipping from Mouser. Course, I bought some other bits-n-bobs that were not available on the Parts Place.
When I found out that part was going to be discontinued, I bought a decent stock of them for experiments.

I need to get my browser bookmarks a little better organized so I don't need to rely on Google searches so much. The Parts Place did not appear during my search. And I had completely forgotten about it. This getting old stuff sure isn't for the faint-of-heart!!
I've never bought from the Parts Place.  Like you, I forget he is in business.

I finally got it all together...now I can't remember where I put it<
VY 73,
Wes

AE6ZM

Sierra Vista, AZ
GL with you building and experiments.

72,

Jim, K8IQY


Shirley Dulcey KE1L
 

Those parts on Mouser must have been snapped up. When I look now all I
see is the TSSOP version. Ham suppliers and eBay sellers may continue
to offer the SOIC for a while, but in the long run designs are going
to have to switch to the smaller package.

Fortunately for builders of the QCX and future QRP Labs products, Hans
already supplies the boards with the surface mount ICs pre-installed.
Switching to TSSOP will require a board redesign but will have no
effect on building the rig. But it could be a pain for people who need
to replace that part on older rigs; the price is likely to increase as
the supply dwindles.

On Wed, Feb 6, 2019 at 8:58 AM Jim Kortge <jim.k8iqy@...> wrote:


On 2/5/2019 6:41 PM, Wes wrote:
Pretty good price Jim, I paid 53.5 cents each, but $8 in shipping
from Mouser. Course, I bought some other bits-n-bobs that were not
available on the Parts Place.
When I found out that part was going to be discontinued, I bought a
decent stock of them for experiments.

I need to get my browser bookmarks a little better organized so I
don't need to rely on Google searches so much. The Parts Place did
not appear during my search. And I had completely forgotten about
it. This getting old stuff sure isn't for the faint-of-heart!!
I've never bought from the Parts Place. Like you, I forget he is in
business.

I finally got it all together...now I can't remember where I put it<
VY 73,
Wes

AE6ZM

Sierra Vista, AZ
GL with you building and experiments.

72,

Jim, K8IQY






Kārlis Goba
 

Why the bleak pessimism? There are other SOIC equivalents like sn74cbt3253 or sn74lvc3253 still around and not phased out as far as I know. 

--
Karlis YL3JG


Kārlis Goba
 

Apologies, I meant SN74CBT3253 and SN74CBTLV3253 for the low voltage (3.3V) version by Texas Instruments, and without the SN prefix by Nexperia. They are still around and kicking.

--
Karlis YL3JG


Shirley Dulcey KE1L
 

The LVC parts are lower voltage which means lower receiver dynamic
range. Not a good tradeoff in most ham designs, though it might be
okay for an ultraportable rig that prioritizes battery life rather
than performance.

The SN74CBT3253 remains available in SOIC for now. But the long term
trend in the industry is toward smaller packages so its days may be
numbered as well. The opinion among hams also seems to be that the ON
version of the part is a better performer as an RF mixer, though I
haven't seen any comparison tests anywhere.

Using these analog switch ICs as RF mixers is an off-label
application, so we can't count on the manufacturers catering to our
needs. But the fact that they are used in huge quantities for other
purposes is what makes them cheap.

I don't see my suggestion that ham designers switch to the TSSOP
package as pessimism, just an acknowledgement of the realities of the
business. Demise of the SOIC may increase the cost of repairing older
radios but that has always been an issue; as electronics manufacturing
shifts the parts to fix older things become harder to get. Just try
finding new vacuum tubes or even 1/2 watt carbon composition resistors
to fix your boat anchors! (Fortunately there are still plenty of used
and NOS tubes at reasonable prices to repair most radios. You can
still get those resistors but they're much more costly than they were
in their heyday.)

On Wed, Feb 6, 2019 at 12:08 PM Kārlis Goba <karlis.goba@...> wrote:

Why the bleak pessimism? There are other SOIC equivalents like sn74cbt3253 or sn74lvc3253 still around and not phased out as far as I know.

--
Karlis YL3JG


Richard G4TGJ
 

For anyone in the UK wanting the FST3253MX Farnell have over 1000 in stock at ~50p but RS has 230 in stock at ~15p. I've just bought 20 which should keep me in Tayloe mixers for a while. No delivery charge with RS.
Mouser has 1600.
--
73
Richard
G4TGJ


Camerart
 

Hi R,
Your message notification came at the same time at the one from RSONLINE confirming my order for the same. Coincidence!
C.