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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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BK Precision 1522 scope: bad input section, no trace
Hi! I just bought an old-school BK 1522 20MHz dual-trace scope on
eBay, and it works great -- at least, half of it. The trace for channel 2 works great, but channel one gives no trace at all. I've narrowed it down to the input circuit board for channel 1 -- the input board on this scope contains the voltage scale switch and input jack, a couple dozen passive components, a transistor or two, and that's about it. The scope contains two such identical boards. They each connect to the rest of the scope via a 4-conductor cable. Disconnecting the input 1 board entirely produces a straight line trace (as if it were plotting GND); reconnecting it makes it disappear. Connecting the input 2 board to the input 1 connector produces the expected effect -- the signal on input 2 displays on the input 1 trace. There are no burned spots, no leaking / puffed out electrolytics, or any other obvious defects. I've reflowed all the solder joints. How can I leverage the fact that I have two identical boards -- one working, one dead -- to find the problem? Thanks a lot! Ben PS -- This was to be my first scope, so all I have is a DMM... |
#3
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BK Precision 1522 scope: bad input section, no trace
It is very common that the input devices, such as the input FET's get easily
damaged in these scopes. When taking measurements, it is very important to take care to not test high voltage areas that are overspec for the scope with the probes. Change the input devices, and check for any other devices in the board that are defective, or just change all the semiconductors. -- Greetings, Jerry Greenberg GLG Technologies GLG ========================================= WebPage http://www.zoom-one.com Electronics http://www.zoom-one.com/electron.htm Instruments http://www.zoom-one.com/glgtech.htm ========================================= "Ben Byer" wrote in message om... Hi! I just bought an old-school BK 1522 20MHz dual-trace scope on eBay, and it works great -- at least, half of it. The trace for channel 2 works great, but channel one gives no trace at all. I've narrowed it down to the input circuit board for channel 1 -- the input board on this scope contains the voltage scale switch and input jack, a couple dozen passive components, a transistor or two, and that's about it. The scope contains two such identical boards. They each connect to the rest of the scope via a 4-conductor cable. Disconnecting the input 1 board entirely produces a straight line trace (as if it were plotting GND); reconnecting it makes it disappear. Connecting the input 2 board to the input 1 connector produces the expected effect -- the signal on input 2 displays on the input 1 trace. There are no burned spots, no leaking / puffed out electrolytics, or any other obvious defects. I've reflowed all the solder joints. How can I leverage the fact that I have two identical boards -- one working, one dead -- to find the problem? Thanks a lot! Ben PS -- This was to be my first scope, so all I have is a DMM... |
#4
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BK Precision 1522 scope: bad input section, no trace
It is very common that the input devices, such as the input FET's get easily
damaged in these scopes. When taking measurements, it is very important to take care to not test high voltage areas that are overspec for the scope with the probes. Change the input devices, and check for any other devices in the board that are defective, or just change all the semiconductors. -- Greetings, Jerry Greenberg GLG Technologies GLG ========================================= WebPage http://www.zoom-one.com Electronics http://www.zoom-one.com/electron.htm Instruments http://www.zoom-one.com/glgtech.htm ========================================= "Ben Byer" wrote in message om... Hi! I just bought an old-school BK 1522 20MHz dual-trace scope on eBay, and it works great -- at least, half of it. The trace for channel 2 works great, but channel one gives no trace at all. I've narrowed it down to the input circuit board for channel 1 -- the input board on this scope contains the voltage scale switch and input jack, a couple dozen passive components, a transistor or two, and that's about it. The scope contains two such identical boards. They each connect to the rest of the scope via a 4-conductor cable. Disconnecting the input 1 board entirely produces a straight line trace (as if it were plotting GND); reconnecting it makes it disappear. Connecting the input 2 board to the input 1 connector produces the expected effect -- the signal on input 2 displays on the input 1 trace. There are no burned spots, no leaking / puffed out electrolytics, or any other obvious defects. I've reflowed all the solder joints. How can I leverage the fact that I have two identical boards -- one working, one dead -- to find the problem? Thanks a lot! Ben PS -- This was to be my first scope, so all I have is a DMM... |
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