Triboost not working in linear boost mode

[tcr77]

Hi folks,
I posted this question on the BYOC forum, but I'm not getting much help there. I built a Triboost using a circuit board I got from a member of this board and all the components from Small Bear. It's all wired up, but only the Germanium and Clean Boost modes work. The middle one (Linear boost) delivers no sound.

I can't easily get the board out to shoot the other side, and since it's working in two of the 3 modes, I don't want to de-solder all the connections. The jumper is in place, though. Hopefully these shots will be helpful for troubleshooting.

Voltages are: 0.0, 0.89, 9.6 on the 2N5088.

Many thanks in advance!











And, yes, I did solder the Ge tranny to the socket, because I couldn't get it to stay put otherwise.

[petemoore]

  Just for good measure I'd request again a showing of hidden traces.
  1 thing is fine when it works, but schematic and layout are another thing..Afaiconcerned they're just fine not included when you don't need them.
  Other than that:
   0.0 Emitter, seems grounded..
  , 0.89 Base seems to be above emitter
  These two voltages might change when [unless the E is actually connected to Gnd.
9.6v..should be half that, so...why not..
  Something isn't distancing it from V+ [wrong value resistor or trace...measure between the C pin and V+ to find R value.
  Could be the base isn't biased. Somehow knowing the bias configuration would help, in the mean time you can measure R values from Base to Gnd. and V+, if they're 'wierd' that'd be a place to start further inspections.
  I'd find the hidden traces first, see if you can try get the designer to cough it up, then trace the one-off like every other 1rst time debugger of these boards {IIRC There ain't no showing of the board traces, you gotta figure the 10k or whatever it is coming off the collector..must be this one..use the DMM to verify the C does connect to the R, that R does connect to...whatever...probably V+?...verify what connections you do and don't have, meausuring 10k [or whatever the Cbias resistor value is] pretty much tests the relevant connections as well as the 10k value as well as show where the trace goes. Where it doesn't go...try every other pad on the board to find this out.
  If the traces of the design have been published, my apologies for past criticism to the designer for not including a trace-show-diagram.

[tcr77]

This PDF

http://buildyourownclone.com/boostinstructions.pdf

contains both a schematic (pg.4) and traces (pg. 6). One discrepancy I see is that the schem calls for a 360 Ohm resistor while the board calls for a 390. There's a 360 in there now, because that's what I received from Small Bear. Would that make a difference?

[tcr77]

I just verified with my DMM that all my solder joints are good and connected to where they should be for that segment of the circuit. Could it be the 390 vs. 360 resistor value that's killing the signal? Which resistor is controlling the voltage to the transistor?

[slacker]

The difference between 360 and 390 Ohms won't do anything. Like Pete said something looks like it's shorting the collector to 9 volts, maybe a bit of solder where it shouldn't be. With no power to the circuit what resistance do you read across the 10k resistor connected to the collector of the 2N5088?

[chris_d]

Depending on what revision that PCB is, you may have one of a small batch of early ones that require some careful trace modification to function correctly?

In my case, the three boosts functioned, but the LED indication did not quite correctly.

If yours does not work at all on the LPB section you may have something else wrong, but should probably at least take a look at the other side of the board and make sure that your traces are not of the earlier flawed version type.

Pictures of the issue i mention here:
http://www.buildyourownclone.com/board/viewtopic.php?t=6527

That may not be helpful to you at all, but it s probably worth ruling out first before you get too deep into desoldering things and whatnot.

-chris

[tcr77]

Thanks for the tips, folks. Turns out I just a had a 10M resistor where I should have had a 1M resistor. The bands on the components are so small that it was nearly impossible to tell the difference b/w blue and green on the third band. I misread it with my DMM several times since it showed up as a decimal. I don't understand why they can't just put numbers on these goddamned things. It seems so pointlessly arcane, like when lawyers use Latin.

But it works now, so that's the important part. Thanks again!