Kenwood TS-520 repair (COMPLETE, SUCCESS): Port over
Postby Mr. Nick » Mon Jul 27, 2015 3:03 pm
Starting this thread to track progress of the TS-520 radio
repair.
520_Manual.pdf
User Manual
(4.73 MiB) Downloaded 1 time
TS-520_service.pdf
Service Manual
(5.32 MiB) Not downloaded yet
Edit: Added User manual and Service Manual. These include schematics for
reference.
Last edited by Mr. Nick on
Fri Oct 23, 2015 2:01 pm, edited 2 times in total.
Postby GoodBuddy1 » Mon Jul 27, 2015 3:07 pm
Do you have a good idea of what's
wrong already?
Postby Mr. Nick » Mon Jul 27, 2015 3:10 pm
Well there is a transistor missing.
I have to get a workable replacement then I have to trace signals through the
unit to find any other issues. So... No... 
Top
Postby Mr. Nick » Wed Aug 19, 2015 3:11 pm
Several Updates from different
dates:
July 17, 2015:
I got a chance to give the radio a once over tonight. From the visual
inspection I was able to find 2 issues so far. The first is that I am pretty
sure the receiver didn't work because Q5 (3sk35) is missing from its socket on
the rf board. The second was a ruptured electrolytic capacitor on the bottom
next to a smaller transformer (16v 470uf). I already replaced the cap with a
new 25v, 470uf I had on hand. The transistor however is some kind of dual gate
FET device. I do not have any. I will have to hunt one down before I continue.
Once I replace Q5 I will work on getting the Rx portion functional. I have yet
to apply power, wanted to check things out first.
--------------------------------------------------
August 1, 2015:
I was poking around in it last night and it looks like the vfo has nothing
coming out. The oscilloscope shows a flat line when the vfo led is lit. I was
working on pulling that section out until the wife got home. It has only 3
connections. What looks like 2 power wires and the main signal out. I don't
know what the voltage from the red wire is supposed to be. Thinking about it
now it may be where ever that is coming from as the red wire only has about 3
volts on it and I am pretty sure that should be higher.
I checked a few voltages and it looks like power is good at least from the main
supply. It does look like someone else hand their hands in it from some cut and
resoldered wires in various locations.
I will continue on it as I have time. I think I may need to wear a dust mask or
something because some kind of dust or otherwise irritates my throat when
working on it in close quarters. Not allergies just irritation that lasts a
while. Weird.
-------------------------------------------------
August 2, 2015:
Spent a couple hours today on it. I was checking out all of the switches and
dial potentiometers. Used contact cleaner on them and tried fixing some of the
contacts that were not really touching very well.
The vfo requires 9 volts when I was seeing only 3. I traced it back to the
fixed channel board. This has the 9 volt regulator circuit on it. I found the
reference 6v zener diode (D3) was shorted so I replaced it with a 5.1v zener in
series with a normal rectifier diode I had on hand. Measured at 6volts drop
when I connected it to a constant current source. This isn't the only issue.
The main pass transistor (Q4) had its base shorted internally to one of its
other terminals. Can't remember which. It wasn't passing any current. I was
thinking I may just replace the whole discrete regulator circuit with a 7809. I
don't have any. I also don't have any suitable PNP transistors as a
replacement.
I found a dual gate MOSFET that may work for Q5 on the rf board. Can't test it
until the regulator is fixed.
Did check the AF board by feeding in a small signal to the DET pin and it did
amplify and output to the speaker with varying levels of loudness based on the
volume knob. So that's good at least.
May be a bit before I can find some replacement components to continue on.
Don't know what happened to this rig.
---------------------------------------------
August 4, 2015:
Tonight:
Replaced the 9 volt regulator circuit with a 5 volt regulator 7805 and a 4 volt
zener diode on its center pin to get 9 volts. The vfo seems to be pulling down
the 14 volt supply now which is feeding the regulator and the regulator gets
hot. I will dig into the vfo next. Some semi conductor may be shorted inside
that can.
a little progress.
-----------------------------------------------
August 7, 2015:
Got the vfo out today and found that Q4 had its base internally shorted to its
emitter. Replaced it with a 2n3904. Q1s gate seems to have been destroyed as
well. Those dual gate FETs are hard to find. I may have to order something with
similar specs. Most of the ones you can order online are tiny surface mount
components.
I am suspecting the unit may have seen some kind of voltage surge on its main
supply.
-----------------------------------------------
August 18, 2015:
I worked on the vfo last night and replaced the dual input jfet 3sk22 with a
single input jfet I had in my bin. It was oscillating then but distorted. Turns
out the second fet or buffer was bad. Internal leakage or something. Replaced
that one too and the vfo came to life. I had previously replaced the output bjt
which was shorted at the base to emitter. That means 3 out of 4 of the
transistors in the vfo were bad. Since the new oscillator transistor didn't
have a substrate bias I wasn't sure how that would effect it. It was varying in
amplitude so I put a 1n914 diode across its gate and ground. This kept the
amplitude constant. It matches the output the manual shows.
This is a little concerning. I have a bad feeling anything that was connected
to the 9 volt regulator which itself failed may be bad. I speculate that the
unit saw some kind of transient or someone plugged it into a 240 outlet.
Something like that.
I am not sure what would cause the base to emitter and gate to drain junctions
to become shorted.
I will likely be making a digikey order soon with jfets and dual gate MOSFETs.
I made a PCB adapter for the MOSFETs because they are tiny surface mount
devices and will require leads. 56cents surface mount vs 14 dollars for the
appropriate thought hole component is the reason for the PCB. There really are
only surface mount versions available.
----------------------------------------------
Postby Mr. Nick » Fri Aug 28, 2015 9:40 pm
August 28, 2015:
Tonight I fixed the carrier board. There was no output. Well there was but at
100mv peak. It is suppose to be closer to 1 volt. The Q2 BJT was shorted
causing no amplification of the 3MHZish signal. Replaced and the output is now
big and strong.
The panel meter has been pegged full right since i started. I fixed that by
fixing the AGC. The issue for this was on the IF board. Q7 JFET's gate was
damage and shorted to drain/source.
After fixing these last 2 items the radio speaker started to produce a static
hiss. Still missing Q5 (the main rf input Amp) for now but I will have my
adapter boards on Monday.
Seems I almost have the receiver portion going. lots of work and learning
so far.
Postby Mr. Nick » Mon Oct 05, 2015 9:15 am
10/04/2015:
Haven't worked on the radio in around 3 weeks. I spend a little time on it
Sunday night looking into why I had no S-Meter deflection when a strong RF
signal was present from the RF generator. I can hear it on the speaker but the
S-meter didn't budge. Found that the was a problem with Gate 2 of Q1 on the IF
board. I swapped it out with the tiny PCB adapter I made and the SMD Dual gate
mosfet I bought from Digikey. The S-meter is now deflecting with a signal
input. However it is not deflecting as high as it should. This may have
something to do with the RF front end of the unit. I will have to look into
this. Once that is resolved I think the receiver should be functional and I
will be able to string an antenna up for listening. Then I will look into transmitting.
I will use the 50ohm wet dummy load I build this weekend for this purpose.
Attached are pictures of the Q1(IF board) transistor mount( was a tight area to
work in ) as well as the Q5 (RF board) replacement which was originally missing
when I got the unit. Just to show how the adapter looks.
Postby Mr. Nick » Tue Oct 06, 2015 8:11 pm
October 6, 2015
Good news well mostly, I caught a cold which is not so good. Any way on Monday
I looked into the weak s meter deflection with the rf signal gen input. I found
that Q9 (dual gate MOSFET) on the IF board had bad gates. The voltages were the
same on all but one pin. Replaced it with another smd part with one of my
little adapter boards. When I turned on the radio after replacing this the s
meter went off the scale, which is good as the rf gen was still attached.
The cal signal was present and audible now as well. However the cal signal was
present even when it shouldn't be with only vfo selected. Looked into this an
hour ago suspected and was correct in that D7 and D8 wired to the vfo switch
were shorted cause voltage to always be present on the cal unit. Replaced those
with 1n4148s. Fixed that issue.
I put a short wire into the ant jack and I am hearing ssb and cw signals.
Looking good. Next I will check out transmit. Just waiting for the caulk to dry
on the dummy load I am making.
I may have to start working on an antenna setup soon. 
Postby Mr. Nick » Thu Oct 08, 2015 3:17 pm
October 8, 2015
Just a quick update.
Last night I adjusted the VFO to be within specs of the 4.9-5.5Mhz and match
the dial.
I was going to look into transmitting.
I connected the 50ohm dummy load to it and attempted to switch the unit to
transmit on tune. There was no output and the IP meter was at 0 for plate
current. Found out that driver tube was cracked. I will need to locate a
12BY7A. This may have been my fault when I was checking things out a couple
months back. Hopefully everything else is okay.
I will likely install a stealth inverted V antenna for at least one band along
the roof line of my house. I am hoping to get okay performance out of it even
when held against wood and painted.
Postby Mr. Nick » Fri Oct 23, 2015 2:00 pm
I replaced the cracked tube and
tested the transmitter using a homemade dummy load. Transmitting seems fine and
I started to practice the tune up procedure. During this I found that the RF
meter was not reading properly. It turned out the POT was bad for the
adjustment on the side.
I verified that there is indeed a problem with the 28mhz and 28.5mhz bands.
They are set 1mhz low. One is in the cb band, the other I don't know.
Everything else seems to be working now otherwise. I get over 100watts out on
all bands based on rms voltage squared over resistance of 50 ohms.
I also built myself a microphone based on an electret mic and a small momentary
switch. Got the 4 pin connector from radio shack.
Some pictures below.
Homemade 50 ohm Dummy load for testing transmit:
Most of the bad components that were replaced:
Rf volt pot was bad too, meter either pegged or was zero. The element
was cracked:
New pot installed and working:
I may update this further with setting up the antenna system and first
contacts. Otherwise, the radio is now working. I have no plans to change the
crystals for the 28 and 28.5Mhz band. I will just not use them
Postby GoodBuddy1 » Fri Oct 23, 2015 9:53 pm
It's great to see you got it up and
running. That looked like a daunting schematic to follow from what I saw.
Where there more bad parts then you expected?
Postby Mr. Nick » Sat Oct 24, 2015 9:39 am
Oh, yes. I was originally told there
was only the band problem. But someone else had their hands o. The radio after
that and ripped out one of the filters. A very expensive filter to sell on
eBay. It goes for over 100 bucks by itself. In the process likely killed the
rest of the radio. There was terrible soldering everywhere. Solderblobs and by
the filter that was removed a trace was ripped off the PCB.
I believe it did work when. Mr mush had it. He handed it off to some
electrician who just sat on it after ripping the part out. Mr. Mush asked if I
could have it, which is how I got it. But of course the sucker was DOA.
Never met the other guy but ugh wtf man. I don't know if he knew he killed it
or not. If he knew I should smack him for being an ass. If he didnt know I
should smack him for being dumb and fat fingered.
I learned a lot in the process so it worked out anyway. The price was right
aside from the cost of replacement components the thing was free.
Total I sunk 20 bucks into it was digikey parts. I still have a lot of spares
so less then that if you only count what I used. $1.80 for the tiny PCBs. Maybe
another 20 bucks for the mic connector, rf adapters, variable pot and grain of
wheat replacement bulbs. I bought some spare tubes off eBay for 10bucks. So
around 50 bucks.
Not terrible but not great. A new radio goes for about 700 dollars.
Pictures:
Enjoy!
