Repair of Kenwood TS-570D Transceiver

[xrunner]

Friend got in touch with me about this radio. It had been disconnected from power and antenna for about 6 months. When he turned it on he could not hear any stations at all on any bands. He said nothing could have happened to it in storage.

When he was here I injected a -73 dBm signal on 16 MHz and indeed there was no indication of it receiving the signal. The "standard" is -73 dBm = S9 on the signal meter. However, as I turned up the signal to -33 dBm we started to hear it. I said well perhaps the antenna relay is bad and I can replace it.

I asked him if it transmitted OK and he said it used to, but he hadn't tried it. When I tried it into a 40 dB attenuator hooked to my spectrum analyzer, it was OK on CW but no modulation could be observed on AM or SSB when talking into the Mic. The ALC indication was banging hard all the way to the right of the meter indication no matter what.

I said leave it with me and I'll get to it when I can. Well today I found that there are three voltage regulators +5, +8, and +12. The +8 reg. had +12 on it's output. Part ordered and will be replaced, then we'll see if that's all that was wrong.

[tkamiya]

ALL radio I repaired had a bad attenuator switch.  Since almost no current flows there, oxidation never get blasted.  I usually play with it 50 times or so then a drop or two of deoxit.  Then play some more.  I never had to replace so far.  Another case, one of the attenuator register was burned crisp.

[xrunner]

ALL radio I repaired had a bad attenuator switch.  Since almost no current flows there, oxidation never get blasted.  I usually play with it 50 times or so then a drop or two of deoxit.  Then play some more.  I never had to replace so far.  Another case, one of the attenuator register was burned crisp.

Ah I see OK, I'll be sure to check it out on this radio. When I get it working again I'll go through many of the service alignments and I'll check whether or not the attenuator is working properly. 

[xrunner]

The 8V regulator parts arrived. The only thing is I couldn't get the original style package that has the thicker plastic-encapsulated tab. This one has the thinner metal tab that is bonded to ground. Will still work but the clamp that holds all three regulators to the case won't hold it tightly. I'll come up with some spacer - any ideas?

[tkamiya]

You can shim it or relocate that piece elsewhere and complete the circuit by short pieces of wire.

I think the answer is whatever IS possible as it's a small radio and as far as I can remember, it is jam packed.

[PA0PBZ]

Can you mount it with long legs and just clip it on the plastic housing? It's hard to see the thickness from the picture.

[xrunner]

Can you mount it with long legs and just clip it on the plastic housing? It's hard to see the thickness from the picture.

Good idea but it won't quite work. 

You can shim it or relocate that piece elsewhere and complete the circuit by short pieces of wire.

I think the answer is whatever IS possible as it's a small radio and as far as I can remember, it is jam packed.

Well here is what I came up with. I cut some thick styrene for the front and put a thin sheet of silicone heat sink sheeting behind. This allowed the clamp to hold all three regulators.

The good news is that the radio now appears to be fully functional - both receiving and transmitting. Receiving a -73 dBm test signal results in nearly an S9, and the modulation is working. The missing 8V affects a lot of systems in the radio.

Next up I'm going to go into the service menu and make a lot of checks such as power, frequency accuracy, and other important parameters.

[xrunner]

Now I'm going through the adjustments. They are done two ways - by direct interaction with adjustable components on the two main circuit boards and a second set through the service menu. To get into the service menu you have to hold down a coupe of buttons while pressing the power on button AND have a jumper installed shorting two pins in a rear jack.

In the picture I'm going through the power output settings via the service menu.

[xrunner]

This morning adjusting the Ref. Osc. which is supposed to be 20 MHz. However the test point and adjustment it is underneath an RF shield which also keeps the components under it at a certain temp. The shield has to be removed to adjust the trimmer so that's' not the greatest thing but it is what it is.

TRX Bench documents this also at around 23m -

[PA0PBZ]

Question: In your first post you said The +8 reg. had +12 on it's output.  Didn't that fry anything?

[xrunner]

Question: In your first post you said The +8 reg. had +12 on it's output.  Didn't that fry anything?

Nothing that I can find. The radio seems to be working just fine now. Apparently the circuitry that used the 8V just ended up being biased wrong, but the voltage wasn't high enough to damage anything.