Kenwood TS-430 - Plenty of Problems

Discussion in 'Radio Circuits, Repair & Performance' started by KD0WQP, Mar 13, 2017.

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  1. KD0WQP

    KD0WQP Ham Member QRZ Page

    Hello all. First post here.

    I recently started working on an old TS-430 since I got my General ticket. Being an old rig, the problems seem to be legion. No, I don't want to replace the rig.

    The first thing I've noticed is poor audio quality on AM receive. From what I've read, this is due to using the SSB filter on AM; this radio doesn't have the AM filter installed. I ordered the optional AM and narrow SSB filters and will install them when they arrive.

    I assumed that I would need to clean the filter relays since the radio hasn't been used in quite a while so I did the 25 ohm resistor "cleaning" procedure by feeding current through the antenna connector for two minutes wile stepping through each band 1Mhz at a time. It seems that the radio receives well through the entire frequency range.

    The next thing I noticed, however, was no receive at all in SSB mode. I traced this down to an intermittent contact in the Wide/Narrow switch. After switching back-and-forth between wide and narrow, SSB started receiving. I suspect this switch shouldn't do anything, though, since there is no narrow filter installed. It does look like that filter was installed at one time in the past - and subsequently removed presumably for sale.

    This is where my first question comes: How do I clean this switches and, if not possible, where might I find a replacement? I found a couple "switch units" on eBay but they're in Bulgaria.

    The next problem was on transmit - horribly distorted SSB transmit. Investigation on the Web pointed me to intermittent solder joints in the PA which I have since re-soldered. I also added the "z wire mod" to prevent the bad solder joints from causing damage in the future.

    Re-soldering the PA solved the SSB transmit distortion, but now AM transmit audio is horribly distorted. Unfortunately I'm not sure where to look next; output power is not fluctuating and SSB audio is clear as a bell - supposedly the two signs of bad solder joints in the PA. I can't seem to find anything on the web about distorted AM transmit audio - but it seems strange that this problem only appeared after working on the PA.

    Would I be correct to suspect that the bias on the PA transistors may need to be re-calibrated? If so, where can I find the procedure?

    I have also read about oscillating 5v and 8v rails when powered with >12v (my power supply is set at 13.8vdc) - the fix being additional capacitance filtering on the voltage supplies - but am not sure if this could cause AM transmit distortion. I suppose to test this theory I could simply turn the power supply voltage down to below 12v.
    Unfortunately I'm not sure which pin of IC9 is the "input."

    Another problem I've noticed has to do with the built-in meter and the RF-gain knob. RF-gain control seems to be operable, though it seems to have quite a small range; less than a quarter-turn of the knob mutes all incoming signals - even the strongest signals (such as a 10w mobile transmitter less than 250 feet away) are muted. Also, as the RF Gain is turned counterclockwise, the signal meter continually moves to the right until the meter is pegged. This seems counter to the effect of a reduced RF input. The ATT switch seems to function correctly, though.

    Also the meter never moves when transmitting on AM or on SSB. The radio is putting out a solid 100w carrier in AM mode (verified with an external meter) and swings to more than 100w in SSB. Even under these conditions, the meter never moves regardless of the position of the ALC/IC switch. I suppose this could be caused by a bad switch as is the case with the Wide/Narrow switch so this is another case where I need to figure out how to clean the internal contacts.

    Further, when transmitting in SSB mode with the speech processor activated, the radio transmits power even with the MIC at zero gain. I haven't listened to a receiver when transmitting in this condition, though, so I'm not sure what kind of audio the radio is producing.

    On another probably unrelated note, I've also noticed that the radio has been modified to allow general receive from 0-30 Mhz. When listening to signals in the extreme low end of the band, I've noticed "dead AM carriers" at 200, 299, 399, 499, and 599 kHz. These signals disappear as soon as I remove the Coax cable so I'm fairly certain they're not internal oscillations. I suppose these signals could be the cause of the general HF hash I've been picking up around my QTH.

    So, to recap the questions:

    How do I repair/clean the switches on the front of the radio?
    Where do I place the 0.1 uF capacitor to smooth the 5v regulator?
    Where should I look to find the cause of distortion on AM?
    Is the meter on the front of the radio operating as expected?
    Should the radio transmit power with no Mic input on SSB with the speech processor enabled?


    Many thanks!
     
    KD4NJA likes this.
  2. KD0WQP

    KD0WQP Ham Member QRZ Page

    BTT.

    Another problem I've noticed is a sharp drop-off at 1700 kHz - tuning down to 1699.99 kHz attenuates basically all signals - though there is no click of any relays in the filter section. Every other band switch causes an audible filter click/switch but not at 1700. Should a relay switch at that frequency or should I look elsewhere to fix the problem?
     
  3. KA5IPF

    KA5IPF Ham Member QRZ Page

    What a list.

    How do I repair/clean the switches on the front of the radio? Replacement is the only option.
    Where do I place the 0.1 uF capacitor to smooth the 5v regulator? Not needed
    Where should I look to find the cause of distortion on AM? Adjust the AM transmit by the book, set to 25w carrier and adjust mic gain to just before the ALC moves
    Is the meter on the front of the radio operating as expected? In RX yes, in TX it depends. If no movement in IC or ALC it could be the switch.
    Should the radio transmit power with no Mic input on SSB with the speech processor enabled? It depends on the setting of the Mic Gain pot and the background noise, could also be Carrier Balance.

    The AM broadcast band filter has abt a 20db pad to prevent overload. It's in the RX BPF on the RF unit which is diode switched.
     
  4. K7TRF

    K7TRF Premium Subscriber QRZ Page

    Even if there's no narrow filter installed the filter selector switch still has to apply the correct control voltage to the filter switching diodes. IOW, an oxidized or otherwise faulty switch contact could still cause problems if the appropriate control voltage isn't provided by the switch in one or both positions. IOW, replacing the switch won't hurt and might help a lot. In the short term you could jumper past the switch so the wide filter is always selected which at least lets you get on with the remainder of your troubleshooting and is fine until you actually purchase another filter.
    That is normal behavior for S meters and RF Gain controls. The S meter reading is really derived from AGC voltage and as you turn down the RF Gain control you alter the AGC loop behavior in such a way that the S meter rises as you've seen. That behavior is not a problem. The small usable range of the RG Gain control suggests receiver sensitivity issues but it really depends on what signals you're using to test the Rx when this happens. If you're connected to a decent antenna or a known signal source (e.g. a 50 uV S9 signal source) and you only have a tiny bit of RF Gain operating range then you likely have receiver sensitivity issues to sort out.

    Yeah, that's a problem to sort out. It could be Carrier Balance adjustment as suggested above but then you'd expect some RF with no audio input in SSB mode with or without the processor engaged.

    Sounds like you've got your hands full with this one. Do you have a copy of the service manual so you can at least check the various alignment steps? Don't jump in and start tweaking settings but it will at least tell you things like key voltages and procedures to check things like carrier balance, processor gain, etc. It really sounds like a good cleaning is your first step. Gently loosening and then re-tightening all the PCB mounting screws is also a good step in rigs of this vintage as board grounding issues can create a host of strange problems.

    Good luck,
    -Dave
     
  5. KD0WQP

    KD0WQP Ham Member QRZ Page


    I wonder if anybody has replaced the switches with individual/discreet DPDT switches. I'll have to tear it apart and see if it's possible.
    I've always been a big fan of over-engineering DC filter caps... I'll have to scope the DC supply and see if it is, indeed, rippling.
    It seems I discovered this last night - with a lower carrier (25-35w) there is no distortion. Seems extremely enemic, though, with a two 2SC2290 transistor PA; I've seen 10-meter amps with two of the same transistors produce a 100w deadkey with no audible distortion..
    I've never seen the meter move with the ALC switch in the IC position.
    I think I had some feedback at the time causing the squeel.
    Too bad there isn't a way to switch that attenuator in and out of the circuit...

    That's not a bad idea - I may give it a shot.

    I tested in the 10 meter band with a mobile transmitter at 10w into a quarter-wave whip in the yard (less than 50 yards from the base of my antenna). Even a quarter-turn of the RF Gain blocks the signal out entirely.

    I think I had squeel/feedback at the time I saw that. I'm going to have to look into it a little more.

    Yeah I have the owners manual and a service manual. The only equipment I have, though, is a DMM, variable voltage supply, and an old Oscilloscope (that I haven't yet tested).
     
  6. KD0WQP

    KD0WQP Ham Member QRZ Page

    I've found an S-6 internal carrier at 21.5614 Mhz. The signal doesn't go away with the antenna disconnected.

    I assume this points to a diode leaking an internal crystal frequency somewhere but I have no idea where to look...
     
  7. KA5IPF

    KA5IPF Ham Member QRZ Page

    I
    It's outside the ham bands so doesn't count. Most multiple mixing receivers will have birdies somewhere. It's the design that puts them out of the frequencies of interest. They can be eliminated with better shielding but you would choke at the cost of the receiver ($10k ish)
     
    KD0WQP likes this.
  8. KD0WQP

    KD0WQP Ham Member QRZ Page

    That's good to know; this is my first "real" Amateur Radio so the only thing I have to compare to is a 10-12m mobile that I haven't used in a few years.

    I got the switches cleaned with some electronic contact cleaner and they're working beautifully now. The meter works when set to IC as well. I also installed the AM filter and that made so much of a difference I'm surprised it was an "option" and not standard. SWL is now at least tolerable. I suspect an external speaker will make it even better.

    I might pick up a narrow SSB filter but for now the standard SSB filter seems to work.

    I think receiver sensitivity is still way down, though; it seems like my handheld SWL radio with telescoping antenna can pick up just about everything the Kenwood can, and the KW is attached to a vertical at 40' off the ground. I did pick up 150 feet of LMR-400 to run to the tower just in case the old RG-8 is losing the signal on the way to the radio.

    But at least I'm slowly making progress.
     
  9. KD0WQP

    KD0WQP Ham Member QRZ Page

    Another thing I've noticed - is I lose ALL receive when I press the RIT button (even more-so than pressing the ATT button). I suspect this could be related to the generally low receive sensitivity.
     
  10. KA5IPF

    KA5IPF Ham Member QRZ Page

    I can't attach the service bulletin but send me an e-mail and I'll send them, especially ASB0902. My first name at my website.

    Oh keep looking there's another birdie.
     

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