Threaded Mode | Linear Mode

Jurgen Keller · 01-06-2016, 10:08 PM

(01-06-2016 02:15 AM)quantalume Wrote: Those are nice images! I always enjoy looking at quality, old boards with their gold-plated traces.

You'll find some more nice boards in my Flickr Stream (you have to scroll down a bit).

(01-06-2016 02:15 AM)quantalume Wrote: The defective board has two inductors which presumably connect to the two adjacent capacitors (you can verify this by following the traces on the back side of the board).

Yes, I've verified that.

(01-06-2016 02:15 AM)quantalume Wrote: One of the first things to check would be those electrolytic capacitors. They should initially indicate a low ohm value when you connect the meter, which rises over time (seconds) as they charge. If the reading doesn't reach megohms after a short while, then they are likely bad. In fact, it's good practice to replace electrolytics that old even if they seem good. You should unsolder one end of the capacitors when checking them.

I will do that measurements on the weekend, when I've digged out the soldering iron. I'm asking myself what the exact specifications of those capacitors are. I can only see 'USA7143H / 50-25 DC'. I googled around a bit but didn't find anything. Any idea?

jebem · (This post was last modified: 01-07-2016 12:37 AM by jebem.)

(01-06-2016 10:08 PM)Jurgen Keller Wrote: I'm asking myself what the exact specifications of those capacitors are. I can only see 'USA7143H / 50-25 DC'. I googled around a bit but didn't find anything. Any idea?

USA7143H:- year 1971 week 43
50 - 25 DC: 50uF, 25 Volt DC

You may cut one of the capacitor legs close to the PCB by using a small cutter.
In this way you can check the issue right away.
If the component is not faulty, just solder it back in place.
It's a small operation that leaves no damage to the component or to the PCB.

Jurgen Keller · 01-15-2016, 09:59 PM

The electrolytic capacitor on PCB2 (near the pins) is fine, resistance rises over time. However, the capacitors on PCB1 (which are of the same type) both show 0 kOhm. So they are faulty I suppose.

Now I have to buy at least the following parts:
1 x Inductor 240 uH
1 x Inductor 470 uH
2 x Electrolytic capacitor 50uF, 25 VDC

jebem · (This post was last modified: 01-16-2016 08:09 AM by jebem.)

(01-15-2016 09:59 PM)Jurgen Keller Wrote: The electrolytic capacitor on PCB2 (near the pins) is fine, resistance rises over time. However, the capacitors on PCB1 (which are of the same type) both show 0 kOhm. So they are faulty I suppose.

Now I have to buy at least the following parts:
1 x Inductor 240 uH
1 x Inductor 470 uH
2 x Electrolytic capacitor 50uF, 25 VDC

Great!
For the caps, the common value is 47uF.
The working voltage must be at least 25Volt to be on the safe side.
Type should be axial for cosmetic reasons meaning it must be electrolytic (tantalum could be used but they are very small and radial, and usually they have much lower internal impedance that can cause other side effects).