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Author Topic: Kenwood TS-520 No receive?? Help  (Read 9555 times)
KB0FSD
Member

Posts: 16




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« on: May 29, 2013, 06:41:45 AM »

Picked up a Kenwood TS-520 over the holiday weekend, was told no TX, no receive.

On the bench, TX shows 65w on 80, 35w on 40, 20-15-10 hover around 25 to 15 watts. Nothing intermittant and all output is solid. (not worried about this problem yet, but mentioning it in case it's tied in with the receive problem?)

The receive: From a dead cold start, it receives (not always) great for about 2-5 seconds then just static. Push in the WWV button and it receives great on that band (30M) only all the way across and no issues. Now if you push the WWV button in and out several times the normal receive will work for 2-5 seconds at times or be completely dead with static.
I have dismantled the WWV switch, cleaned it, nothing broken,  reassembled,  checked switch for continuity A-OK, and same symptoms, no change.

T/R relay was supposedly replaced last year??? Have swapped both relays around and no change!

Thought about a bad solder joint? What board might be culprit??

Still new to trouble shooting major problems, have the service manual, blown up copy of schematic (so I can read it!) and a volt/ohm meter. Googled the no receive problem but the symptoms don't seem to match anything listed???

Anyone familiar with the 520 or know where I should start looking for my problem???

 
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K5EFJ
Member

Posts: 17




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« Reply #1 on: May 29, 2013, 07:47:14 AM »

I'm not good with this either so take anything I say with a grain of salt.  If you have static, your audio circuit is good.  That 2 to 3 seconds of good receive sounds like a capacitor problem
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KE3WD
Member

Posts: 5689




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« Reply #2 on: May 29, 2013, 10:16:57 AM »

Don't write off the relays just because of the hearsay evidence that they were replaced last year. 

Try tapping on the relays with a pencil, small screwdriver handle or insulated spudger tool while listening to the rcvr when hooked to some sort of receiving antenna. 

If the signal goes in and out with the tapping, sure sign of dirty relay contacts. 

Some relays can be opened up and you can clean the contacts easily by running a US dollar bill between them a few times. 


73
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G3RZP
Member

Posts: 7086




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« Reply #3 on: May 29, 2013, 03:22:26 PM »

Note that a 5, 10, 20, 50 or 100 dollar bill produces no better results than a 1! New bills may be slightly better than old ones.
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KG6YV
Member

Posts: 543




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« Reply #4 on: May 29, 2013, 03:31:36 PM »

Kenwood hybrid transceivers are old and need some mild refurb (always).

Trust me I have owned about 15 of them from 520's thru 830's.

1. Check the voltage on the regulated low voltage supply and set it per them manual.  Oh yes surf the google and find a good manual online.
2. Loosen and tighten every single screw that holds down ALL of the boards.  You may even find some that are only finger tight as heat/cooling/age causes them to loosen.  The ground return for all the boards is bonded thru the chassis with all those screws.
3. Clean every switch in the transceiver with de-oxit thoroughly.  I clean the bandswitch segments and the mod switch with several sprays of de-oxit then run them slowly thru the range of contacts 50-60 times at least.
4. The 520 has wire wrap connections on the boards instead of the flakey molex connectors used on the later hybrids so these should bet OK and not causing any intermittents.
5. Check and replace the screen dropping resistors on the finals and the cathode resistors if they are out of spec.  They are carbon comp. resistors and don't age well.  Some 20-30 year old carbon comps. drift higher by as much as 100%.

Check out the yahoo Kenwood 520/820/830 group for help from a good bunch of real experts.

Gud luck,
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KE4DRN
Member

Posts: 3746




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« Reply #5 on: May 29, 2013, 06:05:55 PM »

hi,

Sounds like a good cleaning is in order,
these radios don't like to sit idle, they are born to run!
Most of us use Deoxit or your favorite contact cleaner,
just the smallest drop, avoid getting any of the wafer switches
wet, they will soak it all up and that causes problems.

Take your time and you should have the radio working just fine.

Check the 9 pin male connector on the rear of the radio,
often this connection needs cleaning and that sends the
9v to the VFO.  If it is missing it may have a short bare jumper
at pins 8+9.

Check all the screws on the pc boards, these radios
all have common grounds and sometimes the screws are
a bit loose, back them off and then hand tight.

Manuals are here in pdf no cost

http://www.n6wk.com/kenwood/

Check the meter for the HV level when in
transmit, often the HV caps are at end of life.

Please join other TS-5xx and 8xx hybrid fans

http://groups.yahoo.com/group/TS-520_820_530_830/

you can read all the messages while you wait for list approval.

73 james
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KB0FSD
Member

Posts: 16




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« Reply #6 on: May 30, 2013, 09:34:12 PM »

Well finally had a chance tonite to do some more tinkering on the 520.
Checked and cleaned the relays, clean.. Still nothing!
Loosened screws, tightened screws, same results--nothing.
Removed inspection cover on VFO, sprayed it with cleaner (recommended on several Hybrid site's) Nothing...
Checked for the 9 volts and 3.3 volts on the AVR board, voltages checked good.
No idea what voltages to check and where?

It's been sitting on the bench for over an hour now, in the WWV position playing out the aircraft weather reports like there's no tommorow.

Thanks for all the input all!

Will keep trying to figure it out.

 
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KE3WD
Member

Posts: 5689




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« Reply #7 on: May 31, 2013, 05:30:42 AM »



It's been sitting on the bench for over an hour now, in the WWV position playing out the aircraft weather reports like there's no tommorow.


That must mean that most of the receive section is working.  

Investigate the switching between WWV and the other bands, could be a dirty switch, misaligned, broken contact, something like that.  

Might also be in the Bandswitch...


73
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KE4DRN
Member

Posts: 3746




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« Reply #8 on: May 31, 2013, 04:04:00 PM »

hi,

with the Function switch set to 25Khz,
do you hear the calibrator as you spin the
frequency dial?

Is there a jumper or male plug on the rear of the radio
at the VFO socket 9 pin? (pins 8+9)?

Is the VFO led glowing?

Could be a dirty Function wafer switch.

With the Heater Switch OFF, do you hear the T/R relay
click when you use the SEND switch?

73 james
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KB0FSD
Member

Posts: 16




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« Reply #9 on: May 31, 2013, 09:23:11 PM »

hi,

with the Function switch set to 25Khz,
do you hear the calibrator as you spin the
frequency dial?

Is there a jumper or male plug on the rear of the radio
at the VFO socket 9 pin? (pins 8+9)?

Is the VFO led glowing?

Could be a dirty Function wafer switch.

With the Heater Switch OFF, do you hear the T/R relay
click when you use the SEND switch?

73 james

With the 25Khz on it is working, but only in the wwv position, ham bands it's dead.

Yes there's a jumper on the 8 and 9 pin, solder blob thats grey. Going to redo this first with a good wire jumper and resolder.

VFO led is working.

T/R relays clicking good.

I cleaned all switches, looked for loose and broken wires, nothing. All switches look good with nothing bent or broken.

Going to do some more tests as suggested and will report findings.
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KB0FSD
Member

Posts: 16




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« Reply #10 on: June 02, 2013, 08:44:20 AM »

Checked Q5 on the IF board and found it had some bad voltage readings. Replaced it. Still same bad voltage readings.

Did some more testing and have found the voltages on Q4 and Q5 on the RF board are out of wack, Only one leg on both Q4, Q5 has the proper voltage and thats the 13.4 and the 14.2.

Would Q4 or Q5 if bad give me bad voltages on the rest?? Or do I have a voltage problem somewhere??? The AVR board is still showing 14v and 3.3 per the manual.

If it's a voltage problem? Is there anywhere I can look to find out the voltages at all the Test pins on the boards??? Both the manual and service manual do not list these, sure would help if it did!
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KE3WD
Member

Posts: 5689




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« Reply #11 on: June 02, 2013, 09:54:57 AM »

When you find a bipolar transistor with wrong voltages, replace it and the wrong voltages persist, check all associated resistors, capacitors, diodes, etc. in that stage. 
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K9TW
Member

Posts: 9




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« Reply #12 on: June 08, 2013, 09:46:10 AM »

The gain controlled devices are not bipolar transistors. They are dual gate mosfets.

Need AGC control voltage on Gate 2 and Operating bias on Gate 1. Need high Z meter to accurately measure the AGC bus control voltage at the Gate of Q5 RF amp. Nominally 3.3vdc if RF-1 has been set properly on AVR board. A 11 meg VTVM will pull this down to approx 2.5 vdc or so and drive the S-meter upscale to S4 or so. Use of a lower Z meter on the AGC bus (rail) can literally shut the receiver down.

OK to measure Gate 1 dc operating bias with just about any DMM or analog meter.

KE3WD has mentioned dont trust the relay contacts.  That is good counsel.

If cleaning RL-1 Aux relay (pulling paper wetted with deoxit thru the contacts) and swapping with Ant TR relay does not result in good Gate 1 operating bias voltage then connect a 9vdc transistor radio battery to the RLR terminal post on the RF board. Connect negative lead to chassis ground and touch positive lead to RLR terminal with rig in RX mode and see if the receiver comes alive. If it does, you have bad aux relay contact or bad wire wrap lead wire and that is not very likely.

RLR gets its 9vdc thru NC contact on RL-1 aux relay. The relay gets the 9vdc from the regulated output of the series pass regulator on the AVR board. RLR feeds RB (receiver bias) terminal on the RF board thru resistor voltage divider. RB then supplies operating bias voltage for the dual gate mosfet IF amps on the IF board.

You can buy NOS RL-1 relays from Kens Electronics in Kalamazoo Mich.

Terry K9TW
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K9TW
Member

Posts: 9




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« Reply #13 on: June 08, 2013, 11:07:57 AM »

I forgot to mention. Transistors, mosfets, tubes all like to have correct dc and signal voltages where they use them and that is at their leads and in the case of your Q4 and Q5 that is at the socket pins were the leads interface. You can try removal and re-insert with power off to wipe the leads, but doubt that is your problem. Make sure you observe the orientation of the can tab.

OK to measure supply voltages and the voltages at the wire wrap terminal posts on the boards, but the place it means the most is at the devices. If you have spec voltages at the post then have to move on to the devices.

You mention reading voltages that are "out of wack" at the device sockets/leads with exception of  Drain voltages.

I would be more interested in the exact dc voltages you have on the Gate 1 and 2 and at the Source leads of Q4 and Q5 and what meter you are using.

The point I am trying to make is if you have good RLR, good RB, and good AGC at wire wrap terminals and "out of wack" voltages at Q4 and Q5 gates and source leads then two choices. 1. Install a new device with care as subs may have different lead pin out and 2. Remove the board and look at the soldering at the socket pins.

Removing the RF board is not easy. Before removing see if you can access the socket pin solder on foil side thru the bandswitch boards. Use the Service Manual x-ray views to find the DSGG pads. Under magnification see if you can see any movement when you wiggle the sockets. This is not a typical failure.

There are some resistors involved in the bias and source leads, but they seldom fail or have bad solder connections.

One last possibility to check before looking at socket soldering is that you have lost your HET Osc signal. Very unusual to lose it on all bands. TP-3 is provided to  measure and adjust your Het Osc level on each band. Do you have a RF probe/VTVM or  O-scope? Should have approx 1.0 rf volts at TP-3 on all bands. If no Het Osc signal ( zero)  it is possible someone mis-adjusted all of them but not very likely.

The operating manual tells how to adjust the Het Osc without test gear and the service manual tells how to do it with test gear. Becareful not to crack any cores or rip the formers off their mounts. If you find the cores cracked do not attempt to turn them. I usually apply a drop of lube at edge of the cores before attempting to turn them with the proper alignment tool. If cores are frozen I apply soldering iron tip to them and then turn while hot.

Terry K9TW
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K9TW
Member

Posts: 9




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« Reply #14 on: June 08, 2013, 04:07:29 PM »

Sorry so long. Dont let WWV reception fool you into thinking Het Osc cant be the problem. WWV has is own independent Het Osc not related to bandswitched Het Osc signal I mentioned at TP-3 on RF board. Still suggest you measure Het Osc signal on all bands at TP-3.

If no Het Osc signal at TP-3 make sure you have 14vdc at N14 wire wrap terminal post on RF board. N14 gets its 14vdc from the WWV push button switch when it is in the off or normal position.

Terry K9TW
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