Bun's Lab – Telegram
Bun's Lab
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Electronics projects, vintæg computing, programming and repairs. A minimalist blog of sorts.
@BunsGarden @BunsNook
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It was the 74S00 quad NAND gate. Of course always the last place you look.
I did not have an S series one on hand. I replaced it with a 74F00, I hope that's fine.
Works again!
👍4
Yesterday on the bench: a Soviet made oscilloscope!
Spicy
A thing of beauty and a joy forever.... Except it's dead
It can run on both AC as well as DC. To achieve this it rectifies the AC into DC and then uses the DC in a very early switch mode power supply. The connections that go to the board to the left only go to two rectifier diodes that were placed on there. The board on the right generates an ~8 kHz switching signal to drive T1, T2 which then drive the transformer
Except the oscillator was dead as a dodo.
This is the board to the right with the oscillator for the SMPS.
By process of elimination I found that one of the drive transistors is bad. It's a П 215 PNP germanium transistor.
They can be had for relatively cheap still, so there really is no point in trying to adapt a modern part.
The oscillator runs when taking it out of circuit.
Fixed: my Exact Model 127 Sweep generator.
Really neat thing to have. Where before I used two function generators cobbled together to sweep the IFs of the little Radiola radio, this does everything in one unit, as it provides the ramp of the sweep at an output. You can also precisely dial in the start or stop frequency, and it can do bursts and pulses.
So why didn't I use it? Because it was broken
I thought there was more wrong with it but it turns out, all that was wrong with it was a single bad tantalum 😂