Rectifier testing - UK Vintage Radio Repair and Restoration Discussion Forum

zooterman · 5th Oct 2012, 8:00 pm

Can someone tell me how to test a rectifier, I am messing with a Studer B67 tape deck which has 4 rectifiers which may be defunct.
Thanks.

cmjones01 · 5th Oct 2012, 9:40 pm

A multimeter on resistance or diode test range should do the job. If it's an analogue meter, the meter should show a low resistance when the positive probe is on the 'band' end of the diode (cathode) and the negative probe is on the other end (anode), and it should show a high (tending towards infinite) resistance the other way round.

If it's a digital meter, it should show a low resistance or 'diode test' voltage drop of about 0.4-0.7V with the positive probe on the anode and negative probe on the cathode (end with the band), and a high resistance or 'overrange' indication the other way round.

If the rectifiers are bridge rectifers, they should behave like four diodes in the following way:
- one from each ~ or AC terminal with their anodes on that terminal and cathodes on the + terminal
- one from each ~ or AC terminal with their cathodes on that terminal and anodes on the - terminal.

What's the fault you're looking for? If these are power supply rectifiers, if they're short-circuit then the machine will be overheating its mains transformer or blowing fuses. If they're open-circuit then the DC output from the rectifiers will be low or missing. If the DC outputs are OK, then the rectifiers are unlikely to be your problem.

I hope this helps
Chris

PETERg0rsq · 7th Oct 2012, 9:52 am

Another quick test is to connect a small DC voltage (say 9v or 5v) across the AC connections of the rectifier.

Measure the DC voltage across the DC output of the rectifier with a voltmeter.

You should see a DC voltage, approx 1V lower across the rectifier DC output.

Then reverse the DC supply (swap the leads around) and you should see exactly the same voltage, and polarity, on the DC terminals of the rectifier.

If you see anything else there is a problem in the rectifier!

(note if the rectifier is a Schottky type the difference in input voltage and output voltage will be lower, approx 0.3V drop)

This test can usually be done in circuit (no power!!) with no effect on the result, just watch for smoothing capacitor charging.

Peter

Refugee · 7th Oct 2012, 10:01 am

If there is a transformer connected to the AC terminals the fuse would need to be taken out.

5th Oct 2012, 8:00 pm	#1
zooterman Retired Dormant Member Join Date: Jan 2007 Location: Lampeter, Dyfed, Wales, UK. Posts: 369	Rectifier testing Can someone tell me how to test a rectifier, I am messing with a Studer B67 tape deck which has 4 rectifiers which may be defunct. Thanks.

5th Oct 2012, 9:40 pm	#2
cmjones01 Nonode Join Date: Oct 2008 Location: Warsaw, Poland and Cambridge, UK Posts: 2,681	Re: Rectifier testing A multimeter on resistance or diode test range should do the job. If it's an analogue meter, the meter should show a low resistance when the positive probe is on the 'band' end of the diode (cathode) and the negative probe is on the other end (anode), and it should show a high (tending towards infinite) resistance the other way round. If it's a digital meter, it should show a low resistance or 'diode test' voltage drop of about 0.4-0.7V with the positive probe on the anode and negative probe on the cathode (end with the band), and a high resistance or 'overrange' indication the other way round. If the rectifiers are bridge rectifers, they should behave like four diodes in the following way: - one from each ~ or AC terminal with their anodes on that terminal and cathodes on the + terminal - one from each ~ or AC terminal with their cathodes on that terminal and anodes on the - terminal. What's the fault you're looking for? If these are power supply rectifiers, if they're short-circuit then the machine will be overheating its mains transformer or blowing fuses. If they're open-circuit then the DC output from the rectifiers will be low or missing. If the DC outputs are OK, then the rectifiers are unlikely to be your problem. I hope this helps Chris

7th Oct 2012, 9:52 am	#3
PETERg0rsq Heptode Join Date: Jun 2009 Location: St Helens, Lancashire, UK. Posts: 641	Re: Rectifier testing Another quick test is to connect a small DC voltage (say 9v or 5v) across the AC connections of the rectifier. Measure the DC voltage across the DC output of the rectifier with a voltmeter. You should see a DC voltage, approx 1V lower across the rectifier DC output. Then reverse the DC supply (swap the leads around) and you should see exactly the same voltage, and polarity, on the DC terminals of the rectifier. If you see anything else there is a problem in the rectifier! (note if the rectifier is a Schottky type the difference in input voltage and output voltage will be lower, approx 0.3V drop) This test can usually be done in circuit (no power!!) with no effect on the result, just watch for smoothing capacitor charging. Peter __________________ SPECIALIST.....Knows everything about nothing EXPERT..........Knows nothing about everything Last edited by PETERg0rsq; 7th Oct 2012 at 9:53 am. Reason: added clarity!!

7th Oct 2012, 10:01 am	#4
Refugee Dekatron Join Date: Apr 2012 Location: Worksop, Nottinghamshire, UK. Posts: 5,554	Re: Rectifier testing If there is a transformer connected to the AC terminals the fuse would need to be taken out.