# Duocast: damaged transformer?



## slowpogo (Apr 9, 2021)

I built the Duocast and got nothing from the output jack. After checking everything I can think of it seems to be functioning perfectly -- up until the transformer. Using an audio probe with Gain, Level 1 and Level 2 turned about halfway up I get output all the way up to the transformer primary, and it responds to the low cut and gain pots as expected. The voltage switch has the correct effect, LEDs light up, the high gain switch bumps up the signal as expected.

Not sure it matters but my germanium is Matsushita 2SB171 (hfe 60).

I get audio from pins 1, 2 and 5 of the transformer, but nothing from 6. The dot on the transformer is aligned to the PCB (lower left) and I've reflowed all solder joints. I have continuity between transformer 6 to pin 3 of both Level pots, and from Levels pin 2 to the output jack. There's just no audio going from pin 6 to the Level pots.

I've built a lot of pedals and can usually troubleshoot them, but I'm an EE noob and don't really understand transformers. But I can't find anything wrong except the transformer. Any ideas?


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## slowpogo (Apr 9, 2021)

anyone? feel free to tell me how dumb I am. I'm just looking for some direction to investigate. The wrapping on the transformer was slightly separated. Is that some indication that it was maybe roughed up during shipping or somehow defective?


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## slowpogo (Apr 10, 2021)

alrighty then...I'm going to order a new transformer and see what that does. If I can do anything or provide more information to get a better help response on this forum, please let me know. Thanks


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## dgrainger (Apr 10, 2021)

I mean, you can check basic functionality of a transformer with a continuity check on each coil, but you'd need a signal generator and a scope to verify that it's actually working.


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## slowpogo (Apr 10, 2021)

Thanks, I figured it was not a simple test. The fact that I get full functionality right up to the primary, but nothing from pin 6, seems pretty definitive that there's an issue with the transformer. But as I said, I'm noob-ish and thought I could be missing something. I just hope the current transformer is not too hard to desolder.


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## dgrainger (Apr 10, 2021)

Get some flux and desoldering wick/braid and it should come right off


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## Chuck D. Bones (Apr 11, 2021)

Your transformer looks ok in the pic. 
Before you disassemble anything, let's check the continuity of the transformer coils.  Turn both LEVEL pots to max.  Make sure the ON/OFF switch is in the Engaged position.  Make sure the power is off.  Measure the resistance across the output jack.  If the secondary is good, you should read something around 900Ω.  Now measure the resistance across R15.  If the primary is good, you should read something around 800Ω.

These transformers are fairly robust, but if you tug or twist the leads during installation or handling, you could break the winding inside.  Overheating the lead could desolder the winding inside.  If you end up replacing the transformer, check the coil continuity on the new one before installing it.  1 to 3 is 820Ω nominal; 4 to 6 is 1070Ω nominal.


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## slowpogo (Apr 11, 2021)

I realized last night that I had the wrong value in R15, 8k instead of 33k. They're labeled on the pcb and everything, not sure how I managed that! Could that have done any damage to the transformer? I've since replaced it with the correct value. I checked the other resistors and they're all correct.

I measured as you described. Across R15 I get 796Ω, looks good. Across the output jack I get 13.3kΩ...not so good


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## Chuck D. Bones (Apr 11, 2021)

That incorrect resistor was harmless.  Looks like the secondary is open circuit.  The 13.3kΩ you measured is the two LEVEL pots in parallel.


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## slowpogo (Apr 11, 2021)

Ah yes, 25k-ish in parallel, should have realized. Okay. At least I know. I've got a new transformer coming, was ordering for my Informant build anyway so no biggie. Thanks much!


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## slowpogo (Apr 16, 2021)

update...new transformer, everything's working great. One of the transformer pads lifted so I had to run a jumper but otherwise, piece of cake!


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