BOSS DS-1 led not lighting up

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theblackman
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Post by theblackman »

I have an old DS-1 that I've had for years, everything works fine including switching the effect on and off. The problem is the LED does not turn on even though the LED itself is fine (i pulled it out of the circuit).

I've replaced the zener diode (D2) and resistor (r35) but still doesn't work. If can't figure out why the flip flop would work but not the LED? Any ideas what I should check ?
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Intripped
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Post by Intripped »

did you check the integrity of tracks and wires?
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plush
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Post by plush »

theblackman wrote: ↑17 Dec 2020, 12:30 I have an old DS-1 that I've had for years, everything works fine including switching the effect on and off. The problem is the LED does not turn on even though the LED itself is fine (i pulled it out of the circuit).

I've replaced the zener diode (D2) and resistor (r35) but still doesn't work. If can't figure out why the flip flop would work but not the LED? Any ideas what I should check ?
http://cdn.tonegeek.com/wp-content/uplo ... ematic.png
Does the flip-flop (Q4/Q5, especially Q4) do its job switching the bypass (together with the LED)?
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CheapPedalCollector
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Post by CheapPedalCollector »

Early ones the LED is momentary only, is it an early one?
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theblackman
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Post by theblackman »

CheapPedalCollector wrote: ↑17 Dec 2020, 23:04 Early ones the LED is momentary only, is it an early one?
it's a taiwanese one, i suspect early 90s but i haven't checked the serial or anything.
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theblackman
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Post by theblackman »

plush wrote: ↑17 Dec 2020, 16:07
Does the flip-flop (Q4/Q5, especially Q4) do its job switching the bypass (together with the LED)?
the effect swtiches on and off fine so I thought those transistors would be ok if that is working? do you think it is worth swapping Q4 and Q5 for some other transistors I have on hand?

I can see the voltage at the LED changes from ~200mv to about 3.5V when I flip the switch but for some reason I guess there is no current flowing, does that indicate that Q4 may have a problem? (excuse the gaps in my electronics knowledge)

Thanks for the help everyone!
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theblackman
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Post by theblackman »

Intripped wrote: ↑17 Dec 2020, 15:10 did you check the integrity of tracks and wires?
I have done a little bit, but I will double check the path to ground, I suspect a problem with Q4 but I am unsure how the flip flop is working if there is a problem with it.
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The G
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Post by The G »

It seems that the transistors are doing their job (switching). Also the voltage is changing at the LED, although I think 200mV is a bit too low.
Q4's collector gets a bit of +9V from R30 too. Did you measure the voltages along the whole circuit, the +9V D2 pin, the junction of D2 and R35, the junction of R35 and the LED, Q4 collector and Q4 emiter?
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theblackman
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Post by theblackman »

The G wrote: ↑18 Dec 2020, 00:30 It seems that the transistors are doing their job (switching). Also the voltage is changing at the LED, although I think 200mV is a bit too low.
Q4's collector gets a bit of +9V from R30 too. Did you measure the voltages along the whole circuit, the +9V D2 pin, the junction of D2 and R35, the junction of R35 and the LED, Q4 collector and Q4 emiter?
it's around 3.5V when switched on (200mv when off). but if i remember rightly somehow was 4.5v at the cathode, which i thought was a bit weird ... I will check again tonight and make a bit more of a formal log. thanks for the help
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plush
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Post by plush »

theblackman wrote: ↑18 Dec 2020, 03:12
The G wrote: ↑18 Dec 2020, 00:30 It seems that the transistors are doing their job (switching). Also the voltage is changing at the LED, although I think 200mV is a bit too low.
Q4's collector gets a bit of +9V from R30 too. Did you measure the voltages along the whole circuit, the +9V D2 pin, the junction of D2 and R35, the junction of R35 and the LED, Q4 collector and Q4 emiter?
it's around 3.5V when switched on (200mv when off). but if i remember rightly somehow was 4.5v at the cathode, which i thought was a bit weird ... I will check again tonight and make a bit more of a formal log. thanks for the help
Either D2 or Q4 is dead. I bet it's Q4.
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theblackman
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Post by theblackman »

i pulled Q4 and tested it, it's ok. I tried a bc549 (making sure to use the right pins) and it makes no difference.. D2 is new as I replaced it. it was marked as a 1/2W 5.1V diode and at least looks like a zener. I also tried bridging D2 to see if the LED lights up to no avail.

a conundrum for sure. must be something i'm missing.
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theblackman
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Post by theblackman »

alright folks, thanks for the help.

the problem was i mixed up a 1n4148 with a zener :slap: AND also the LED was broken. it still sounds like muddy shit but hey at least the led works now!!
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