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Ten Tec Delta 580 reduced output problem

Discussion in 'Radio Circuits, Repair & Performance' started by GM0MOP, Sep 1, 2019.

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  1. GM0MOP

    GM0MOP Ham Member QRZ Page

    I have another radio to repair. It is a TenTec Delta 580. I have had this radio for a few years from early 2010, and it worked great. Output was full 100W, and worked many good contacts with this rig.

    I sold it to someone locally, and he had it for a couple of years, and he said the output is reduced to almost nil. I bought it back.

    I connected it up to a dummy load, and yes indeed, the output on all band is hardly there, but on 15M and 20M, there is about 1 watt output. When key down, at first there is absolutely no output, but then after about 10 sec - 20sec, there is some output coming out pushing the output needle to about 1 Watt.

    I opened it up, and had a look but couldn't see anything abnormal or broken. But when I felt the heap sink at the back of the rig, it was very hot. This made me think, maybe the output transistors are OK, putting out the full power, but something is blocking it? - like SWR bridge potent meter gone bad, and blocking full output? - just a guess.

    Or indeed, the output transistors are dead? - then it makes me wonder, how the heat sink gets very hot with just 1- 2 watts output for about a minute or two key down?

    What do you think?

    TNK & 73
  2. K5DH

    K5DH Ham Member QRZ Page

    Corroded bandswitch wafer contacts on the Low Pass Filter board? Or corrosion on the RCA connector where the RG-174/U coaxial cable exits the PA module? I've seen both of these issues with Ten Tec rigs in the past. Worth a look.

    Could also be bad PA transistors.
  3. GM0MOP

    GM0MOP Ham Member QRZ Page

    Will have a look at them as your suggestion. Thank you so much.
    Best 73

  4. GM0MOP

    GM0MOP Ham Member QRZ Page

    Had an interesting CW QSO with about 1 Watt from the Delta 580 with a station at southern England.
    Got 559, and good solid contact.

    But I still would like to repair the 580 for its full 100 Watts output.
    This used to be a great rig working DX.
  5. GM0MOP

    GM0MOP Ham Member QRZ Page

    I opened the top and bottom panel, and had close look at the wafer, but there were no sign of corrosion, and I couldn't spot any rca plugs either.

    I will get the current amp meter connected to the power cable, and key up again to check what sort of current the Delta is drawing.

    If p.a. Transistors ok, then it should draw a lot of current when keyed up with full power setting.

    If it draws hardly any current at all, then it makes me to think the p.a. Transistors are not working.

    The manual talks about adjusting SWR bridge in the output of the Delta. But it does not explain what it is for. Any ideas?

    Tks 73
  6. GM0MOP

    GM0MOP Ham Member QRZ Page

    I did more checking on the Delta 580. Here are observed points.

    1. On receive, it draws 1.05 A

    2. On transmit with carrier switch pulled out, mode CW, immediately it draws 4.0-4.3A

    3. With ALC about 12 o'clock position, and carrier knob turned all the way to the max, the current remains the same at 4.3A

    4. On power meter with dummy load reading, power output reads about 50 mW - 100mW

    5. The heat sink at the back gets luke warm.

    6. Couldn't see any disconnected cables, sign of burns or smokes at all. Rotary wafer contacts seems all clean too.

    7. I put a RF field strength meter very close to the 580 while transmitting, but there was no sign of any RF in the meter.

    I couldn't locate where the drive module was. I thought the drive module should give out some 5-6 Watts, if working properly. But 50mW -100mW is just way too low output for the driver if is working OK. Is it that something is blocking the output? - such as SWR bridge gone faulty? Then I would have thought the RF field strength meter would have picked up some sign of RF. But none.

    It looks like I must locate the TX drive module, and check if the drive module is outputting any RF into the P.A. first.

    Any ideas or thoughts?

    Tnx & 73
    Last edited: Sep 13, 2019
  7. GM0MOP

    GM0MOP Ham Member QRZ Page

    Every night when I had a small free time, I was looking at this problem of my Ten Tec Delta. I have been reading the service manual, and looking at the circuit diagram, but couldn't really spot the cause of the problem.

    So I decided to grab my DMM, and keep checking all the caps first, and yes, I got the Electrolytic Cap going into the P.A. Module C22, and it supposed to be 22uF, but it had gone off. The DMMs were reading OL, and I got the Transistor and Caps Tester out, and read it. It was showing readings in ohms not uF.

    So, that C22 Electrolytic had become a resistor, needing urgent replacement. I searched my parts draws, but don't have that value 22uF at 35V, so need to place an order, and replace it.

    Hopefully that will bring it back to full 100W output Ten Tec Delta.

    Will update.
  8. GM0MOP

    GM0MOP Ham Member QRZ Page

    That cap on the P.A. of the Delta is now a resistor. There is no reading of uF.
    It is 100 ohms on my Tr/Cap/Resistor tester, and shows up as a resistor.

    Attached Files:

  9. K5DH

    K5DH Ham Member QRZ Page

    Cut the (+) lead of the cap and see if the transmitter comes to life. I'd replace that cap regardless.
  10. GM0MOP

    GM0MOP Ham Member QRZ Page

    Replaced the 22uF cap. with a high quality Panasonic cap. Unfortunately the Transmitter didn't come back.
    Looks like the P.A. is needing new P.A. Transistors.

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