|FT301 - 2 problem boards sent to me in April 2014
- The two boards were repaired -- details below: (NOTE: I do mail
order repairs of older solid state equipment such as FT301, Ten Tec
Argonauts (505- 515) and Atlas 210 x and some other older radios
|HAMeLECTRONICS MAGAZINE (.COM)
www.earlandrews.com (these are mirror sites)
April 17th 2014
|These are the two RF boards that were sent to me in the MAIL. From USA to Canada its about $9 to $10 in postage. Going back to USA it is about the same. I think this is
about the cheapest way to send boards to me from USA. CERTAINLY.. DON'T use UPS or FEDEX or any commercial courier from USA. Reason: The Office of Homeland
Securities Paper work to get things up here to Canada. The post office doesnt seem to charge for the paper work or..they don't fill out the paper work. Whatever
reason: if sending parts or circuit boards or even entire radios up here for me to repair or purchase..use the post office. Its much much cheaper.
I think in USA its called First Class mail. -- You have to fill out a little green customs slip as per above. IF YOU PUT DOWN: HAM RADIO PARTS OR AMATEUR RADIO
PARTS PARTS-- THERE WILL BE NO CUSTOMS FEES. This box and the cards did not carry with it any other tariffs or anything.
|The S meter pins and just stays pinned. Works ok on transmit.
The 7400 nand gate was bad. It was bad in both boards actually. The reason the S meter was pinning was a shorted switching diode D102. Actually..
D102 measures as a 12 ohm resistance when measured with an ohmeter (with leads in either polarity of test). I got some clues as to what part(s) of the
circuit were problematic by analysing my DC measurements that I made on both boards.-- THE OTHER BOARD (right) was dead on receive but worked
intermittently after I changed the 7400 nand gate (used in TR switching)- I then changed the mixer dg mosfet and the board worked fine again on receive.
|The extender board is being used to aid in trouble shooting these RF
Boards I am working on.
John Nery WA1ESO makes these boards and Ive been using them now
for awhile. I just checked and they are still on ebay and probably listed
on qth.com classified ads as well. He is in Rhode Island USA.
|The first major step in trouble shooting a circuit is a DC analysis. There are two DC analysis models to determine. #1 is during receive and
#2 is during transmit. -- so what I do when Im real serious about a job is I draw a chart and note down the measurements I take. First I use a
healthy circuit board and note down its measurements. I save this chart with the manual in my files for future reference.
|Above are the 18 measurements I made with my VOM (DC voltages) of the healthy RF board. The 1 to 18 represents the 18 card edge connector
pins where the measurements were taken.
The First Circuit board I worked on was the S meter PINNING board. I changed out the 7400 ttl gate as I thought it might be hanging up (latched
perhaps) and when I tested the IC with my new (from ebay china) IC tester..it did test bad. So..I made a socket for the IC so that it would be
easier to change (if ever there was a next time). The main fault was Diode D102. it had a short that actually measured 12 ohms. So I changed
the diode to another new 1S1555 diode (which I keep in stock here) - The way I found the bad diode was just taking a guess at where the
problem area might be on the board..then I took my healthy board and the bad board..set them up on the bench side by side and using the
VOM on the ohms scale and on the diode scale..I began making comparison measurements and I found the shorted diode.
|The 7400 nand gate was pulled and tested and found to be defective. I then made an IC socket out of machined pin strip of 40 pin 2.54
mm round female Pin Header. - I do this for transistors and dual gate mosfets as well. If they get blown once it could happen again.
|The board that was "dead"on receive had two
problems. The 7400 nand gate was defective and the
mixer transistor was defective.
First I replaced the NAND gate. What happens after
this is the board worked on receive but if I
transmitted even for a second.. the receive would
I did suspect that one of the two dual gate mosfets
was defective - either that..or they just got over
loaded on receive and would latch up and perhaps it
was a faulty capacitor.
So I built a transistor socket for the dual gate mosfet
mixer as shown above. That allowed me to replace
the component and see what difference a new one
I did replace the 3SK40 original part with a 3N211 and
the receive was now good and I could go from
transmit mode to receive and back and forth no
problem. I put the old 3sk40 into the socket and the
old problem returned.
THIS IS ACTUALLY an interesting intermittent kind of
problem. Just goes to show that sometimes a
component will work fine then cut out and quit!
Intermittent kinds of problems can drive a person
around the bend! It boils down to divide and
conquer. This is one reason why I like working on
older stuff and discrete components and I take on
small projects like circuit cards. I have lots of
flexibility in how I approach the repairs and I can
swap out parts and try this and that ect.
So..problem solved. The defective 3SK40 was then
put in my JUNK TRANSISTORS LITTLE BIN.
WHAT I DO WHEN I MAKE ONE OF THESE TRANSISTOR
sockets I take some grey JB weld epoxy and dab
some of it around the socket to keep things held
A big advantage of a socket is (for people like me)
who try different things..I try different dg mosfets to
see how I can improve the receiver front end.
Through experimentation..I have found the SFE1612
dual gate mosfet to be about the best one I have
found to use in front end of receivers. The 3N211 is
just about as good - and my BF981 with radial leads
soldered on is a pretty close 3rd. A picture of the
BF981 with the soldered on leads is shown right.
The advantage of the BF981 is that it is a good part
and quite inexpensive to buy. I sell them (tested) at
$2 each from my little shop operation here.
The reason I test them is there are some bad parts
that get out on the market from China. One other
ham I know (who works on stuff) told me he doesnt
care if the parts are counterfeit -- just as long as
they work!! - See my LINKS above right about bad
BF981s comming out of China!
I have written the Chinese suppliers and they did
give me my money back after I returned the
parts..but it is a bit of a lengthy procedure. One
company just took my word for it. I took alot of
pictures and posted them on a web page and after
telling him that 6 out of the 30 I had ordered were
bad parts..he gave me a refund for the 6 bad ones
without having to send the parts back.
|I cut some leads off some cheap imported 1N914 type diodes and used them to make
radial leads for the bf 981 dg mosfet transistor. The complete article on this mod is here.
Be careful however..
there are some bad imported parts out there. I got a couple of bad batches of BF981s
..that article can be referenced here.
|NOTICE the green mark I
placed on the 3N211 in the
above photo. It means a dg
mosfet I have tested. The
reason I test these parts is
that there are some bad
ones comming out of China.
Most are good but there
are bad batches of parts so
I actually plug them in to
test them ..or I use my new
tester (from ebay/China)
and I short the two gates
together and test the dg
mosfet just like I would a jfet
and that is how I test them
|It is actually like solving a mystery when you get these defective circuit boards and you
start to analyse them (DC analysis). You see what the measurements of a healthy board
are then you compare them to the problem board measurements and you try to figure out
which components could be causing these conditions.
I have had a good number of emails from fellows who were having low power output
from their FT301s. - The problem could start here on this RF board. I am actually ordering
in some 2SC741s (C741) transistors to repair one such RF board which has between 1/2
to only 1/3 rd of the power output it should have on transmit. I "suspect"the 2sc741 may
be anemic -- and I will build a transistor socket and try different 2SC741s to see if I can
get the board to put out a proper transmit signal. If that doesnt work..I will try the other
transistor and if that doesnt work..well..maybe its a switching diode or something. As
long as I have ONE GOOD BOARD and one defective board..I can sit down with the
ohmeter and measure suspect portions of the circuit (resistance measurements) in order
to find something that is out of whack! Thats how I found the defective D102 (12 ohm
diode) with one of the subject boards.
AC ANALYSIS WILL BE DONE AT A LATER ON to determine where the amplification of the
RF low level transmit signal is not occurring properly.
WHEN I GO TO WORK ON THE CIRCUIT BOARD WITH THE LOW POWER OUTPUT PROBLEM
(on transmit).. I will bring the oscilloscope on line and trace the RF transmit signal
through the circuit with the good circuit board first ..then with the bad circuit card in the
circuit and I will find out specifically where the low amplification problem occur ie.
which transistor isnt doing its job. Then I will have to find out whether its the transistor
itself or maybe its a capacitor or a switching diode or maybe even a transformer.
I will make notes on my SHOP SCHEMATIC of the RF levels at various test points..ie see
the schematic on this page near the top of the page. The Green Squares are where Im
going to test for the amplitude of the RF signal as I trace it through the circuit.
|A DC analysis is the first step in trouble shooting! -- Well ..actually
maybe the second step! - The first step is a visual inspection. A
close visual inspectoin.
Once you ascertain that everything "looks normal" and there are
no shorts or solder bridges on the circuit board ect ..then you do
the DC analysis. Use a voltmeter and make a chart to note down
the voltages and then do your measurements of the card edge
connector points first. Then..compare the good card
measurements with the defective card measurements. This can
be most easily done with an extender card which brings
everything to easy access.
IF you dont have a good card to compare with your defective
card-- then you can measure the card edge connnector points
with NO card plugged in and get the DC voltages present ..then
plug the card in and get the measurements with the defective
card plugged in and do some analysis as to what could be
happening with the circuit and what part of the circuit seems to
be out of whack. -- I HAVE THE LUXURY HERE IN MY SHOP of lots
of spare parts, spare circuit boards for the FT301, test equipment,
extender cards ect. -- IF you try doing the work yourself and it
doesnt work out..you can always contact me for an estimate. I
work at only $10 per hour and I often just cap the repair costs for
you -- TO MAKE IT WORTHWHILE for you to have me do the repair.
I am retired on civil service pension and I do these things as
Keeps my mind sharp and I enjoy doing these activities. Service
to others is important. Its not good to isolate ones self!
|Below I analyse the measurements and try and figure out what might be going on. The whole idea is to divide and conquer.
Try and narrow down the search for the defects.
With these two circuit cards I was working on.. the DC analysis was all I had to use. I did not have to turn on the oscilloscope to try
and trace the signal through the circuit.
|Below Schematic of the RF Board. RED squares are
marking defective componments ie Q103 on one of
the boards and D102 on the other board.
|The green squares are key points that I will
be measuring when I trace the transmit
signal through one of the boards to find the
spot where amplification of the rf transmit
signal is inadaquet. (AC ANALYSIS METHOD)
|IF you dont have an extender card..you can still do the
measurements from the bottom side of the radio on the card edge
connector. The pins are marked from 1 to 18.
On board measurements without an extender card can be
done..however..it is more time consuming. You have to reach in
with your test probe or possibly..solder a little piece of wire on the
component you are going to test measure in order to reach the
circuit board when plugged in and powered up.
-- takes more time as I said! I have built my own extender cards and
you can see some ideas on my homebrew versions on this page.
|The RF board with the pinned S meter repair was performed by removing the defective 7400 TTL NAND gate (used in TR switching) and as
well the switching DIODE Q102 - I sell the 1S1555 diodes for $1.25 each and the 7400 nand gates for 50 cents each. So that is what the
materials cost. Labour charge 2 hours $20 --- I don't charge to set up the radio ect. --
The RF board with that receive was DEAD at first and then later intermittent after I changed another defective 7400 TTL nand gate - was
repaired by removing Q103 the 3SK40 - I then made a 4 pin transistor socket and used a 3N211 DG mosfet in its place and the RF board
once again was working on receive. Since this was a more complicated repair this time I charged 2.5 hours in labour and for the dual gate
mosfet I charged only $5 ---> I gave the fellow an SFE1612 dual gate mosfet..top quality and only $5 from my shop. 3N211s are good as well
but I charge $7.50 for those.
SO..IF YOU (the readers) WANT TO SEND ME ANY FT 301 circuit boards to trouble shoot and repair you can write me an email at the
following: email@example.com --> I also work on older Ten Tec Argonaut circuit boards in a similar way.
I pretty well have all the parts for these older VINTAGE Solid State radios. I SELL PARTS TOO in small quanitites for those who want to do
the repairs or some scratch building of circuits. MY BIG SUPERLIST (LINK HERE) HAS MOST OF MY INVENTORY LISTED.
|IN CONCLUSION: summary of the trouble shooting on these 2
RF Boards for the FT-301
|73 Earl VE3AB
Elliot Lake, Ontario
north of Michigan state.
|The warmer months are now here April 20th
today! and for the next 6 months I will be
doing a reduced work load indoors (in my
shop) but I still work at selling parts and doing
some small repairs.
|Loved the article could this have been caused by front end overload.
|Here is a diode protection circuit (very commonly
used) to protect the front end of a receiver.
Most of the time only two diodes are used back to
back..ie Ten Tec Argonauts use only 2 diodes.
The problem with using only 2 diodes is the
strong signals from close by can overload the 2
diode system. Even strong foreign Broadcast
signals on 40 meters might act in such a way as
to generate noise from the diodes.
With 4 diodes ...2 one way..2 the other way..the
overloading voltage spikes will be chopped down
to about 1.4 v peak or about 2.8 volts peak to
peak and strong signals on the radio bands wont
affect the circuit (unless its really close by large
signal..in which case..the diodes will come in to
play..which is a good thing).
This circuit could be attached to the RF board of
the FT301 on pin 4 - RX in line.