Need suggestions troubleshooting a partial VCC short

[Test Point]

Hey all...I need assistance..........I could be a hero if I can come up with something to locate a partial short on some mixers we have at my job....They are B*******ringer mixers and several of them have a 300 ohm or so short to ground on the +15 volt rail. it could be any one of hundreds of components that is partially shorted and trying to localize the problem by cutting traces is an almost impossibility...I thought I remembered something on this board about someone building a short tracer (and if so would this trace/locate a partial short). Before I came to this place to work last year, they had scrapped about a dozen of these mixers because of this same problem so it looks like something that is endemic to this series of mixers.....I know, I know...the best B****ringer mixer is a scrapped mixer but it would make the techs some money if we had a way of actually being able to cost effectively trace the problem and get these back on the shelves so some sucker...er I mean, some customer, can put it to use.....any ideas would be greatly appreciated....
Thanks all
TP

 

[PRR]

> a 300 ohm or so short to ground on the +15 volt rail.

Well, a +15V supply should be able to pull 300 ohms, so the "300" reading is an artifact of your test meter.

Break the +15 output and try 100 ohms and 1K between supply and load. If you get 0.7V and 0.6V, it is a forward junction, transistor or chip.

ALL the sick mixers are sick on the +15V side? That has to be a clue. Most of the board is symmetric + and - 15V, so what is different that all the failures are on the + side? Obvious suspects are meter and logic systems. Or it could be a bad silk-screen, one cap (happens to be on +15V) has been installed backward, but didn't hard-fail right away.

Assuming you are used to 15V shocks and are pretty sure there is no fatal power-line leakage, so you can work with power ON:

Obviously feel every part. Whatever is sucking it down may be running hot.

You could try using a VERY high-resolution voltmeter, feed +15V via a 100 ohm resistor, and put probes directly on each + rail cap. Resistance in copper traces will give the lowest voltage on the most hungry part. But the difference could be microvolts.

Follow the + rail and start unsoldering one leg of all the rail caps, while watching a meter.