Golden Rules of Troubleshooting

Yep. When I do something wrong, I'm consistent. As I previously ranted, when I find one bad cap of a type and value, I replace *ALL* the caps of the same type and value. My time is more expensive than the extra caps.

Actually, the machine ran quite nicely for a day or two the first time I put the caps in backwards. Eventually, it started acting strangely so I retreived it from the customers. All 4 caps were bulging. So, I replaced all 4 caps again, putting them in backwards again. That's when I noticed that they were getting hot, which prompted my initial Usenet posting. I too would have expected at least a small explosion, but nothing happened.

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Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

Nice that there were no explosions - I'm sure your customer would have been nonplussed.

(ducking from the coffee explosion)

John ;-#)#

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Interisting it ran at all.

It is easy to get into a bad pattern of doing things. A coworker and I were repairing some flouresence lights in the plant. Got to one and put in new tubes and it did not come on. This did not phase us as we often will get a bad tube or so as there are thousands in the plant we often will replace over 100 tubes in a day. Sometimes we get bad tubes so put in another set and still no light. Decided it was the ballast, so replaced that. Still no light. Knew we had power as there were about 20 other lights in the room. Replaced the ballast 2 more times and sitll no light. This ballast had been replaced before as there were several places where the wires were spliced together with wire nuts. One would thing with only 8 wires it would be easy to get it going. Got time to go home. I went up the next day by myself and decided to try one more time. This time I removed all the wires and instead of just going by the color of the wires, actually trace the wiring out. This time it lite just fine.

What we were doing wrong was just matching the wire colors and as it had been replaced before the colors did not go to the same place.

Peter,

Who in their right mind would still be using one of these? They were considered to be an awful amps back in the 70s. One I saw burned down a house. The carbon resistors caught fire and there happened to be a curtain draped across the top of the amplifier. After seeing this amp, I refused to work on them.

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1a. Trust nobody (except your certificate authority). 1b. Believe no one. 1c. Presume nothing. 1d. Ignore fashionable explanations. 1e. Distrust authority. 1f. Ignore all advice. 1g. Test all new replacement components.

I never make the same mistake twice. Five or six times is my average.

Nope. Clean the device first. Depending on the type of filth, that can be blowing off the dust with compressed air, or washing with a household cleaner to remove fingerprints, dirt, crud, slime, food, whatever. Cleaning allows you time to inspect the device, where you might visually find the problem. Often, the problems go away with the filth. Customers don't believe that anything has been repaired unless it's clean.

Instead of beating on the box, try turning it upside down and shaking. If you hear something rattle around, you've either found the problem, or what's left of some component. Loose screws and spare parts on new electronics are amazingly common.

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Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

Ah, they ain't no how as bad as all that these days. Between the various mo ds, Factory and susequent, they have been rendered pretty bullet-proof, ver y stable, and as simple SS amps go, fairly melifluous. They were made in th e uncounted tens of thousands, and uncounted thousands survive. With a few hours of simple work and not much cost, a decent 50+ watt amp may be had. A s it happens, I keep two (full mods) that see very rough service, and have done so in one case for 2 years of 24/7 use in a desert climate, not condit ioned. 100F+ from may to November. It now sits in my shop system seeing abo ut 3 hours per week, these days.

Who would put a curtain over an amp capable of frying an egg in the first p lace?? That smacks of terminal idiocy.

Peter Wieck Melrose Park, PA

Give him credit for at least swapping out indicator bulbs.

There always seems to come a point when people stop updating the stickers inside the cabinet or the service books with all updates, past problems and more importantly field modifications and why they were done. This seems to happen around the time the safety switches start wear out and get bypassed or panels and covers start to go missing.

What? You don't like my method of documenting changes? I think it's been like that since at least 2001.

Incidentally, I use a special ink for the purpose, that fades to invisibility in about a year. It helps keep the manuals nice and clean.

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Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

Personally I wouldn't use an ST-120 simply because I find capacitor-coupled amps to sound muddy, and yeah - I hated working on the things. Piece of crap really.

Prefer direct-coupled amps (with a competent protection circuit!) although I do like an autoformer coupled McIntosh...

Mark Z.

Funny how certain things trigger a memory of something forgotten for years. I had a Hitachi brand receiver that the customer said blew out several spe akers on one side. I checked the outputs, nothing shorted so I hooked up s ome cheap TV speakers at low volume and there was no DC to speak of on eith er side and it was clean and clear. I let it run a couple of hours and sud denly there was a loud hum, pop, and one TV speaker that puked it's voice c oil. This was direct coupled amp with no type of speaker protection. Ende d up junking it.

ha. Love the metal can transistor diagram. At least these aren't drawn on paper bags or cardboard and then thrown away.

They should make heated pens for writing on thermal paper.

That scribbling wasn't one of mine. I usually draw an isometric scribbling of the transistor or IC so that one can tell if it's a top or bottom view. I think the red markings on the various drawings are mine. Red is useful because it disappears when copied.

Ummm... They do. It's called a soldering iron. However, there's a trick to using a soldering iron for writing. Be sure to grab the correct end of the soldering iron. The rest is self evident and easy.

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Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

What the color of highlighter that would copy solid black even though you could still read the original?

The copiers here are just color scanner/printers so they don't have the same spectral sensitivity as the old machines so I can't test.

Too hot and the thermal paper cycles back to white. It does weird things when heated to the transition temp range.

I don't know and too lazy to test it on my copier.

Interesting stuff:

I have an (old) Canon PC785 mono copier which should work. However, I don't have any highlighters to try.

Too hot and the paper catches fire. As I recall, the paper was black or brown before it started burning. I just tried it with some thermal receipt printer paper. It didn't go back to white.

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Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

Maybe I've been hanging out around too many manager or business types, but I'd suggest:

Find out if a working new (or used) example of the item in question is available, and what it costs.

Under a certain amount, it won't pay to spend time fixing it, unless there are some other circumstances involved. (It was grandma's radio, or whatever.)

Between that amount and some other, really high amount, it might pay to spend time fixing it.

Above that really high amount, they are either wanting confirmation that it is broken, so they can persuade their boss to buy a new one, OR hoping to blame you for an inability to fix it, so *you* have to buy the new one.

Just because you're paranoid doesn't mean that they *aren't* out to get you.

Matt Roberds

For that, they are going to need weapons. I mean like the government has.

That is the way I have looked at lots of things. The repair parts often cost more than the origional item. At work there was a motor and gear box of around 1/2 HP. To get a new motor or gear box actually cost within $ 5 of a whole new motor and gearbox. Then the company would have to pay the mechanic over $ 40 an hour to rebuild the unit as they were always replaced as a unit.

Soldering iron?

Mike.