Ancestors

Toot

Written by Christian Gudrian on 2025-01-05 at 09:59

It’s alive! For the most part, that is. Turns out one half of one H-bridge in the interface is broken: M3 won’t turn right. Let’s check the transistors.

[#]FischertechnikComputing #fischertechnik

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Descendants

Written by Christian Gudrian on 2025-01-05 at 10:15

They don’t make #PCBs like they used to.

[#]pcb #soldering #pcbrouting

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Written by Christian Gudrian on 2025-01-05 at 11:01

Output Q6 of the 8-bit shift register IC4 only delivers around 1.6V to the base of T6 instead of 5V. And now I wonder which of the two parts are broken.

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Written by Christian Gudrian on 2025-01-05 at 11:51

Without T6 the voltage is back to 5V. So I guess that's it.

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Written by root42 on 2025-01-05 at 10:20

@cgudrian suddenly I want to eat spaghetti…

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Written by Christian Gudrian on 2025-01-05 at 12:08

Dang! Even with a replacement transistor the voltage at the gate is back to 1.6V…

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Written by Christian Gudrian on 2025-01-05 at 12:59

I've narrowed it somewhat down to transistor T18: if it's placed the voltage at the gate drops to 1.56V. If I remove it the voltage is 5V. But even if I replace T18, the voltage drop occurs. Maybe D11 is broken?

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Written by Christian Gudrian on 2025-01-05 at 13:47

Found it. D12 is shorted.

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Written by Christian Gudrian on 2025-01-05 at 14:11

Using a replacement diode I've found in my #Busch electronic 2070 studio center the output level at the shift register is now back to nearly 5V.

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Written by Christian Gudrian on 2025-01-05 at 14:29

Sigh. Now M3 won't turn in the other direction…

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Written by Christian Gudrian on 2025-01-05 at 19:13

Turns out one BD136 apparently got a little bit too hot. I’ve replaced it with one from the PC interface which I’m going to fix later.

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Written by root42 on 2025-01-05 at 19:53

@cgudrian awesome!

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Written by Christian Gudrian on 2025-01-05 at 20:06

@root42 It took 35 years. But here we are!

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