Justin,
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I think you have it figured out.
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During receive, the "TX" signal should be near 0 volts.? An AND gate output only goes high when both input pins are high, so all 4 AND gates should have outputs low when not transmitting.? Would have to be a blown 74ACT08 unless there were some pins left unsoldered.? So replace the 74AC08 and see if it starts working, it probably wiill.
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Depending on what happened, it could be some of the BS170's got damaged.? If you ground the BS170 gates, the supply current should go down.
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It's also possible that CLK0 or CLK1 IO cells from the Si5351 got blown, though that's less likely.? Maybe look at CLK0 and CLK1 with a scope or diode RF probe, should both have some RF on them at the transmit frequency when attempting to transmit.
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Jerry, KE7ER
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On Sat, Jan 11, 2025 at 01:27 PM, Justin Giorgi wrote:
Hey Folks,
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I think I know the issue but need a sanity check - the gate voltage at the BS170s should be 0V on receive, correct?
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I just built a QDX and I'm only transmitting about 0.5W. Receive current is very high, 0.36A and the PA transistors are heating up.
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I see 0V on the gate for one pair of BS170s, 1.5V on the other. Signals into the 74ACT08 quad-and look normal. I'm thinking I damaged one of the and gates on that side and the gate voltage isn't being driven to 0V on receive.
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When I remove the 74ACT08 gate voltage floats up to 12V on all the BS170s. I think that's normal for this type of transistor.
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Thanks in advance for your help!
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73. AI6YM
