help with surf pi kit no sound

[Qiaozhi]

do you mean q2 on my board and parts list it irf9640 or do you mean 2n3906 q1 ?

On the schematic (from Silverdog's website) the reference designators are jumbled together, and I assumed that Q2 was the BJT, and the MOSFET was Q1. However, looking at the PCB silkscreen, I see that it's the other way round.

Have a look at the partial schematic below where I've marked the transistor that has most likely been inserted incorrectly. This is Q1 on the PCB silkscreen.

[Tepco]

This also may be relevant, happened more than once:


http://www.geotech1.com/forums/showt...594#post171594

[Qiaozhi]

This also may be relevant, happened more than once:


http://www.geotech1.com/forums/showt...594#post171594

I think Alcartraz's problem is a different one, as he basically has no audio output. Unfortunately he doesn't have a scope, otherwise we could have debugged this much more quickly and easily. With a large metal target near the coil, the preamp output is changing on the voltmeter, but the outputs of the sample gates are not. This points the finger of suspicion at the sample timing pulse circuitry (based around U4), which also generates the audio tone. However, U4 is driven by the TX oscillator via a 2N3906. My educated guess is that this transistor is inserted incorrectly.

[Tepco]

Most probably this is the case. I mentioned another possibility just because under some (unfortunate) conditions, that is, 555 chip way out of spec or output stage partially damaged, 2N3906 may stay in on state all the time, completely blocking signal to timing stage and producing exactly same symptom. Actually happened to me, just before that i blew 555 output by mistake, signal is still being sufficient for MOSFET drive, but this stage around Q1 failed to operate. Again, oscilloscope issue, as usual...

[alcartraz]

q1 tests 255 on meter check and was in the right way ?

[Qiaozhi]

q1 tests 255 on meter check and was in the right way ?

In that case the problem is either located in the circuitry of U4, or it's the same problem that Tepco experienced.

[alcartraz]

ok so i will try the volts to collector and see what they are

[alcartraz]

collector - 4.36 bias +11.22 emitter + 11.11

[Qiaozhi]

collector - 4.36 bias +11.22 emitter + 11.11

Measuring these points with a voltmeter is not very informative, as the TX pulse width is very short compared to the TX period.
Can you post a clear in-focus image of your PCB, just in case someone can spot the bleeding obvious?

[alcartraz]

my board hope this is clear enough please note r3 is underneath but is there !

[Tepco]

Check twice where you soldered R3, connected to pin 4 instead of 3 will cause exactly same symptom and similar voltage readings you have. Voltages you measured are strange, indicating transistor is nonconducting, or maybe faulty (possible B-E breakdown, despite you measured it on Hfe test, peculiarity of some DMM types, intended to measure only working component). Certainly not failure type I described earlier.

[Qiaozhi]

Check twice where you soldered R3, connected to pin 4 instead of 3 will cause exactly same symptom and similar voltage readings you have. Voltages you measured are strange, indicating transistor is nonconducting, or maybe faulty (possible B-E breakdown, despite you measured it on Hfe test, peculiarity of some DMM types, intended to measure only working component). Certainly not failure type I described earlier.

I agree. The fault definitely must be located in this area, despite what the meter indicates.

Alcartraz - Please try replacing Q1 with a new transistor and move R3 to the top side of the PCB.

[Luuk]

I have been closely following this thread because I have the exact same problem with my surf pi 1.2 since the beginning.
Now that Qiaozhi has narrowed it down to Q1 I took mine and had a good look at it with the schematics in hand.
The leg of Q1 that goes to R4 are right next to each other and were soldered seperately I now bridge soldered them and..........UREKA!!!!
now my detector works like a charm and even the delay which never made any difference now works.
I have to thank Qiaozhi for his dedication and patience with this matter. It really shows a lot of character. I salute you sir.

[Qiaozhi]

I have been closely following this thread because I have the exact same problem with my surf pi 1.2 since the beginning.
Now that Qiaozhi has narrowed it down to Q1 I took mine and had a good look at it with the schematics in hand.
The leg of Q1 that goes to R4 are right next to each other and were soldered seperately I now bridge soldered them and..........UREKA!!!!
now my detector works like a charm and even the delay which never made any difference now works.
I have to thank Qiaozhi for his dedication and patience with this matter. It really shows a lot of character. I salute you sir.

I just did a continuity test between Q1 emitter and R4 on a blank PCB, and the connection is good. Therefore, it sounds like you either had a break in the track, or there was a dry joint.
At least that's one Surf-PI which is now working, and helps to confirm that Acartraz's problem must be a similar issue.
Thanks for the feedback.

[alcartraz]

ok i wish mine was that simple new q1 resistor back in place and still the same made no difference and tried a new coil as well