Repair method

Might be helpful to know what the problem is. I repair some boards for a commercial operation, that has machines that use them all over the place. In theory, these need the rest of the machine as well, but by providing these boards with power on the bench, and then simulating the inputs with switches, the CPU clock and strobe signals with a couple of 555 timers and the output loads with power resistors with LEDs across them, I am able to carry out full diagnostic checks on every aspect of the board's operation, and repair them with absolute confidence. Might be possible to do the same - especially if you are likely to have to do more ??

Arfa

The first step to any effective troubleshooting is to understand the function of the circuit. Without that info you can't really do very much. Next you have to understand the individual components and their relation to the function of the circuit. What does the board do? What are its inputs and outputs? What components are these ICs and transistors that you listed?

Leonard

problem.

Here's a thought...... maybe only practical if the IC's are through-hole (not surface mount). I was faced with a similar problem which involved a car wash facility with about a dozen exact duplicate PCB's (and one spare!). Instead of trying to reinvent the entire operation (no schematics or manuals, of course), I noted that new IC's were available for about $.30 each, and the transistors were even less. Just change them all! Didn't take much more time than first troubleshooting and then repairing (which involved replacing something anyhow) Dumb, stupid and lazy? You bet! But, hey.... I could get the car wash up and running pretty darn quick. Old Chief Lynn

What's wrong with the boards? A DMM with a diode check function is probably the best tool for the job, just test all the transistors, they're the most likely fault in a machine like that which drives motors or lamps.

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In this scenario, your best approach might be to get a known good board and record (sketch) the Huntron waveforms on each of the ICs and transistors. Then you can compare the waveforms on the bad boards to the good one and come up with a likely bad component.

Another approach could be to try to reverse engineer the circuit and draw a schematic. That would certainly help you to analyze the problems. The circuit schematic would also allow you to design and build a test setup that would simulate normal inputs and allow you to analyze the outputs.

What kind of ICs are on the boards? Download datasheets from the internet to help you determine what's working and what isn't.

A way that I've used in the past to reverse engineer a board and determine a schematic for it, is to photocopy the print side, then draw on the actual parts, but in schematic form rather than physical form. You can then derive the schematic trace by trace, scribbling them out on the photocopy as you go, using a coloured felt tip pen. From the number of components on the board, and the simple logic function ICs, should be practical in your case. I suppose these days, you could probably do the same thing with a scanner rather than photocopier.

Arfa

"russ lavergne" bravely wrote to "All" (25 Jan 06 21:40:46) --- on the heady topic of "Re: Repair method"

rl> From: "russ lavergne" rl> Xref: core-easynews sci.electronics.repair:356515

rl> Well, this board is one of five that controls a ring of lights. But I rl> can't work on it while it is put toghter. I don't have a schematic rl> and the chips are 74HC14 74HC273 74HC373 and Ten Tip22, one other rl> transitor, two electrolytics, and 8 ceramic caps next to the IC's. Is rl> there no way to troubleshoot without power and schemtics? rl> Thanks rl> Russ

With such few jellybean IC's might it not be logical to simply change them all wholesale style and never develop a migrain over it? It is an infallible way to fix it after all!

A*s*i*m*o*v

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