Скачать или смотреть More Fault-Finding on the Fluke 8600A Multimeter

Having (in a previous video) fixed the 1MHz clock generator, I tested the meter and found that it wasn't switching ranges properly. The range switches should make the decimal points in the display change, and should operate reed relays and CMOS multiplexers to do the actual range selection inside the meter. Also, when in AUTO range mode, the meter should auto-select ranges and automatically control the relays. But it doesn't. Something is wrong with the range selection mechanism.

Looking at the schematic, there's a ROM, U9, part number 376061, which is driven from the switches and controls the relays. OK, so is that the cause of the problem? Well, yes. I re-seated it in its socket because I suspected more bad connections. But it's too far gone for that to fix anything. Pins are corroded and broken off, probably due to the proximity of the leaky NiCad battery (four D-cells).

So how can I fix this? The ROM is a bipolar PROM, 7488 or something similar, but it has been programmed by Fluke with the binary data pattern that it needs to control those relays and CMOS multiplexers. If I was to replace the chip, I'd need to program the new one, and to do that I'd need to read the old one. So I'll most likely solder the old chip to a DIL header and plug that into a replacement (turned-pin) socket.