Another 2517 low receive issue

D16 and D17 should not be testing as zeners, those are regular switching diodes. At what voltage do they zener? The datasheet shows a reverse voltage rating of 30v.

There will NEVER be 8v on the gain pot. The three components circled in green form a voltage divider. In RX, there should always be 8v on the left side of R233 and never more than 3.2v on the right side of it. That means there will never be more than 3.2v on the gain pot.

Here is a DC simulation with the pot maxed (counterclockwise). Here, it is putting the entire 1k in parallel with R291. The wiper and high side should both be at 2v.


If we then swing the pot all the way down (fully clockwise in the radio), the wiper is at ground and the high side sees 3.2v


And if I set the pot half way, I get this (pointless adding these pics because the images are the same besides the voltages on the left, I know)


So now we have a voltage control between 0v and 2v on the wiper. Take a look at the bias resistors at Q17 (circled in blue in the schematic), they are another voltage divider. That divider puts 2.1v at the base. When the RF gain pot is turned all the way up (wired for MINIMUM wiper voltage), the base of Q17 has the most current through it. When the gain pot is turned down (increasing the wiper voltage), it will cause less voltage drop across R72 meaning there is less bias current and less gain.

For example, with no voltage at the wiper, the base voltage (2.1v) minus the Vbe drop puts 1.4v across the 1k resistor, so 1.4mA of bias. If the pot is set to half way, there is 2.1v-0.7v-1.2v= 0.2v across R72 (0.2mA of bias).

edited to make schematic pic smaller so it loads faster, my bad lol

Hawkeye351 said:

I tried to touch up L5 but it does absolutely nothing for receive,

Click to expand...

Unhook one end each of D16 and D17. See if L5 exhibits a peak now. L5 has no internal capacitor to go bad. If it won't show even a shallow peak there's a fault of some sort on its input side, most likely.

Or maybe the antenna was connected during a storm when a neighbor's tree was stuck? Burned insulation on L5 will reduce sensitivity, and turning the slug won't affect the signal level.

73

nomadradio said:

Unhook one end each of D16 and D17. See if L5 exhibits a peak now. L5 has no internal capacitor to go bad. If it won't show even a shallow peak there's a fault of some sort on its input side, most likely.

Or maybe the antenna was connected during a storm when a neighbor's tree was stuck? Burned insulation on L5 will reduce sensitivity, and turning the slug won't affect the signal level.

73

Click to expand...

If an RF signal generator is available I'd inject a test signal right before the 1st mixer then work backwards towards the antenna connector.

If that inductor is bad, wouldn't be the first time for this symptom. L41 in the TS-530/830 series Kenwood hybrids and a couple of them used in the Tempo 2020 seem to be prone to burnout from excessive input signal.

do you have a way of checking how deaf the radio is?

Like, a signal generator with a calibrated output.

put a 1K tone into the radio at 30% modulation and see how far down it can hear.

you should be able to hear at least down to around -115dbm and im used to galaxy receivers still picking up a faint signal (like i can tell when i turn the RF output on and off) at -127dbm.

LC

I don't see C180 on that list, its a tantalum cap.

If you want to play with the gain, there are a couple ways to do it according to the datasheet. The RC between pins 6 and 9 increase negative feedback and reduce gain, so increasing R219 would increase the gain. Pins 5 and 6 provide access to the internal feedback path and lowering R220 will also increase gain. The datasheet says that shorting pin 5 to 6 leads to open loop gain (max gain), which makes sense because all of the signal that would provide negative feedback is shunted to ground via the cap at pin 5. See note 2.

Didn't change C9? Its directly between the chip's output on pin 9 and the speaker.

A 'scope would reveal at a glance if that were causing trouble, just comparing what goes into it with what comes out of it.

73

Figured out the gain. Excel calc attached.



Reuploaded post, had to correct a typo in picture 2 and double check everything.

Edit: Been playing with the calculator for a bit now. I'd say if you mess with the series RC, change the cap, not the resistor. Smaller cap makes more gain. Going from 4.7nF to 1nF has about the same effect as going from 3.3k to 1Mohm. Both provide a little under 4dB change.

Then ignore it. It only adds 2.2uF to the 22uF next to it. Someone correctly chose not to waste the money there.