Circuit Board Testing

[111Robin]

I have a problem with my 1970's Sun analyser, possible fault with a circuit board. I have enquired online with companies that offer board testing and repairs but this stuff is too old for them to be bothered with. I'm just hoping that someone might know of an old school electrical engineer who could check the boards and components and repair as required. The boards are dated late 70's/early 80's.

20200327_140042 by Robin Derrick, on Flickr

20200327_140102 by Robin Derrick, on Flickr

[Spider]

There is a company in the US who refurbishes them. They seem to have all the repair manuals etc for all the Sun gear.

I'll see if I ca track them down again.

[111Robin]

Thanks, I really want it done in the UK if possible. The person I bought the machine from is an ex-Sun engineer in the States but he's going through a bad time with his health so I don't want to bother him with it. He has spare boards he is willing to send but I'd like to see if I can have these checked first.

[snoopy64]

Look for vintage radio folk... to test for a faulty component you don't need to understand how the board works necessarily... I find old TV and radio guys/gals brilliant at this sort of stuff...

[111Robin]

Look for vintage radio folk... to test for a faulty component you don't need to understand how the board works necessarily... I find old TV and radio guys/gals brilliant at this sort of stuff...

Good idea, I was concerned that the lack of a circuit diagram would be an issue. I can trace the tracks for continuity but testing the components is beyond me, the resistors should be easy enough but capacitors etc. I haven't a clue.

[surfblue63]

Is it the light, or are the resistors R73 and R74 (top right) a little burnt?

[111Robin]

I see what you mean, it is just the shadow from the component next to them though.

[iain1967s]

First step with old electronics is to replace the electrolytic capacitors. C1 and C2 in this case.

[111Robin]

First step with old electronics is to replace the electrolytic capacitors. C1 and C2 in this case.

Do these degrade over time more than any of the other components ?.

[smithyrc30]

First step with old electronics is to replace the electrolytic capacitors. C1 and C2 in this case.

Do these degrade over time more than any of the other components ?.

Yes. The electrolyte dries out and they lose their capacitance value. In extreme cases they split.

[111Robin]

First step with old electronics is to replace the electrolytic capacitors. C1 and C2 in this case.

Do these degrade over time more than any of the other components ?.

Yes. The electrolyte dries out and they lose their capacitance value. In extreme cases they split.

Thanks, I'll make a note of that. Without appearing too ignorant, what are the black rectangular items with multiple connections ?.

[smithyrc30]

Do these degrade over time more than any of the other components ?.

Yes. The electrolyte dries out and they lose their capacitance value. In extreme cases they split.

Thanks, I'll make a note of that. Without appearing too ignorant, what are the black rectangular items with multiple connections ?.

Commonly called IC's or Integrated Circuits. Generally they will have a specific function, like a time/clock or an amplifier. In its simplest form it would be a transistor capacitor and resistor all in one handy module. Like an NE555, which is a simplistic timer. On the top of each you will see a number, fire that into google and in most cases you will be able to see the internal circuit and what each pin does. They are based on a common Dual Inline pattern which means that not every leg will do something in a lot of cases.

[111Robin]

I'm assuming this is your area of expertise ?. Do you have a background in electronics ?.

[smithyrc30]

Sorry, no, not my usual area of operation. I am a mechanical engineer but spent a lot of time working in powertrain development at Land Rover then Jaguar with early fuel injection equipment that frequently did not function as intended. So when the boxes did not do what was expected you had to find out why and how to make it do what you wanted, when you wanted and it sort of happened there.

When I was a mere strap of a youth I used to mess about with old electronic equipment with my brother, looking back I wonder sometimes how we survived. Back off old TV, radio, 'gramophone' prod around with the AVO meter or the oscilloscope , plug it in and switch it on .....
What could possibly go wrong? AVO probes on the high voltage coils of the TV tube? No problem until the inevitable bang and magic smoke waft followed by the stupid grins....

Looking at the board picture there is nothing that shouts "I have died" at you but the two electrolytics do look a little swollen. Given the board is fortyish years old, changing out the caps would not be a bad thing. At that age it will have used and been designed to use leaded solder in the joints, so you will need to use this type to change them. The stuff nowadays is lead free and does not play so well with the leaded type. The circuit itself is not that complicated, a few logic ICs and a couple of voltage comparators, just busy. These days 90% of that would be contained in one IC the size of one of the LM339 units.

[111Robin]

Thanks, interesting background you have, appreciate the insight into the unknown world of electronics, cheers.