Another 2517 low receive issue

[Hawkeye351]

Got a different Galaxy DX 2517 on the desk today showing the same symptom as the last 2517.

Symptom:
Low receive (sensitivity and volume) in all modes.

Everything else works as it should. Transmit is around 50w PEP (SSB around 35w).

I've already checked the usual,
Switches
Controls
Wires
Wire connectors
8v regulator
Audio IC (7222ap)
Obvious loose/cracked solder connections
All of that seems fine, no funky stuff going on and everything is firmly in place.

Already did an alignment on it, just low receive volume and sensitivity.

Here are some pics of the solder side and some suspicious things. Yes, I noticed that regulator mod strapped across the Passthrough regulator, I haven't done any work on it yet but that will be yanked out.









I'm going to continue to look it over with hopes of figuring it out, lol...

By the way, the red wire beside JN13 on the switchboard does have constant 8v.

Only thing I noticed was that there is no 8v on the wiper of the RF gain control, RF gain only drops what little bit of receive there is now down once the control is around the 10 o'clock position. From wide open to the 10 o'clock position there is no change in what little receive I currently have. Volume has to be almost wide open (3 o'clock position) to hear stations comfortably.

What's you guys/girls opinions?

 

[Hawkeye351]

By the way, what's the purpose of that blue cap just to the right of the black ground wire in picture 3? I've never seen that before in any other 2517.

 

[Hawkeye351]

I'm getting 8v on Q17 and the 1k resistor next to it, and I'm getting a constant 8v on the red wire next to cn13 on the switchboard.

I plugged my external speaker into the PA jack and still have to crank volume almost wide open. This usually means the audio IC (8) is bad, but all the voltages on IC8 pins show as good. Still no 8v on the wiper of the RF gain.

 

[Cable Guy]

Does pa work?

Nevermind.

Scope the audio chain from the chip toward the speaker? Maybe a bad coupling cap?

 

[brandon7861]

I'm getting 8v on Q17 and the 1k resistor next to it, and I'm getting a constant 8v on the red wire next to cn13 on the switchboard.

I plugged my external speaker into the PA jack and still have to crank volume almost wide open. This usually means the audio IC (8) is bad, but all the voltages on IC8 pins show as good. Still no 8v on the wiper of the RF gain.

If you are getting 8v on the 1k resistor at the emitter of Q17, chances are Q17 is toast. The base bias looks like it would be putting 2.2v at the base, which would put 1.6v at the emitter. The RF gain pot is a voltage divider and (with its series resistor) could never supply 8v to the emitter, so I think it is safe to assume that 8v is coming from a shorted Q17.

 

[Hawkeye351]

I checked Q44 which is mentioned several times as being a known fault for this issue. It's more like just low volume, the receive seems like it's there and fine. Just have to turn volume almost wide open.

Q44 shows nothing on all leads. IC8 leads show the right voltages. This transistor is known to have high leakage over time.

There are only 2 of the 10v electrolytic caps and only 4 of the 16v caps, the rest are 25v, I may replace those 6 caps and try again.

Question, does anyone have a pic of the audio path for this radio? Also, anyone have an E-Cap cheat diagram like we have for the 3600 boards?

Another question:
I thought the RF gain was supposed to have a constant 8v on the wiper? I have 0v on the RF gain wiper. Actually 0v on all three leads of the RF gain control, but I do have the 8v on the 1st IF (Q17).

 

[Hawkeye351]

I'll replace Q17 and try that. Thank you guys for jumping in.

 

[Hawkeye351]

Q17
Emitter - 1.46v
Collector - 8.29
Base - 2.2v

Lead of the 1k resistor closest to the Q17 shows 1.46v.

 

[brandon7861]

Ok that sounds right. That transistor is pobably good then. Earlier when you said you had 8v it and the 1k next to it, I assumed it was shorted and passing full supply to the emitter.

 

[brandon7861]

Another question:
I thought the RF gain was supposed to have a constant 8v on the wiper? I have 0v on the RF gain wiper. Actually 0v on all three leads of the RF gain control, but I do have the 8v on the 1st IF (Q17).

The RF gain pot gets 8v through R233 creating a voltage divider with the pot and R291 that "should" supply 0 to 2v to the emitter. I believe this voltage serves to raise the emitter voltage of Q17 to effectively control the bias.

One thing that stands out to me is the base-emitter difference of .74v. That seems a tad high to me like the transistor is turned on too hard, and in that case, it might not have much gain.

I think the next move is to figure out why the RF gain pot has no voltage. Maybe if we get that fixed, we can slightly increase the emitter voltage and bring the transistor back into a higher gain region. I do recall Lou's book talking about using more bias to reduce gain instead of less bias, and that stands out here.

 

[Hawkeye351]

R233

3.64v on rear lead.
8.72v on the front edge lead.

 

[brandon7861]

That 3.6v would correspond to an open wiper contact. R291 is in parallel with the bottom half of the pot, so the output side of R233 would be pulled lower than that in any case. Having 3.6v there tells me that the only load R233 sees is the 1k pot and not what is also connected to its wiper.

Edit: unless the wiper position is zero

 

[brandon7861]

and since R233 is connected to the pot, a voltage there should mean there is a voltage on one of the pot legs. You said all three legs have zero volts. Double check that.

 

[Hawkeye351]

The connector beside R233,
R1, R2, G all three go to the RF gain control.

R1 shows 3.64,
R2 shows 0.01
G is ground.

 

[brandon7861]

Thats interesting because even if the wiper were not making contact, there should still be a little voltage there. If Q17 emitter has 1.46v, the node between R72 and R291 should be half that, which is the wiper contact lead. Is the pot cranked to one side drawing it down? Center the gain pot and check again