Harrison HP 6202B Power Supply – revisited

After doing a quick repair yesterday – a sleepless night, because of the out of spec ripple. Well, not quite that bad. But typically, all HP instruments hold up to standard, it would be a big surprise if this one can’t be brought back into spec.

First, desoldered all of the capacitors (they used a lot of solder!), and checked them – surprisingly enough, they still work perfectly fine, all 1967 vintage.
Next item, the recifier diodes – some might be leaky. Therefore, just replaced them with “modern” 1N4004. But this didn’t cure the ripple.

Next item, the 6202B has a reference circuit, and, the output had 10 mV noise – ripple. That’s far too much, and did not fully feed through to the output.
What caused this issue? – the defective capacitor (see earlier post) is the filter cap for the reference. Seems the replacement cap doesn’t give the same filtering – just added a bigger capacitor in parallel.

The result – at about 50% load (2 mV per DIV, sorry, don’t have a better scope here)
6202B improved noise

About 0.8 mVpp, estimated 0.25-0.3 mVrms. Amazing. Fully working again.

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