SG-1144/U Signal Generator

©Brooke Clarke, N6GCE

Front	Inside

Description

This Signal generator is of solid state construction and has continous frequency coverage from 50 kHz to 80 MHz.
It has a built in frequency counter and AM and FM modulation.  The RF output can be set from 100 nano Volts to 1 Volt into 50 Ohms.

DOA

The SG1144U arrived DOA and that's how it was sold on eBay.  I have seen a couple more of these DOA on eBay so maybe there is a design problem, or a common mode of abuse?

The C3 tantalum capacitor on the A2A2 board was shorted.  This caused a couple of the diodes feeding it to draw excess current blowing the 1A line fuse within about a second of turning on the power.  Steps in troubleshooting were:

• operate normally - fuse blows right away
• open top cover and unplug J1 from power supply module, replace fuse, plug-in and turn on - nothing, turn off, unplug - fuse was OK.
• plug J1 back in, remove all pc cards and disconnect connectors on the 3 boxes - when turned on fuse blows right away.
• (This is not a good method, but worked for me) install a 5A fuse and power on with all connectors connected, smoke from the A2A2 board, shut down quickley.  The diodes could be seen to be black and some of the PC board.  Someone else had replaced the diodes, BUT DID NOT REPLACE THE SHORTED 10 uF-35V Tantalum cap.

If you have the same symptoms, just remove the power supply assembly (unplug J1 and remove 4 screws) and check all the diodes and Tantalum caps.

After replacing 4 diodes and 2 caps (RS 276-1102 1N4003 , RS 272-1434A 1 uF - 35WVDC) SG1144U appears to be working.

Calibration

The next step to to see how well calibrated this sig gen is.
Photo of Logimetrics Model 920-S101 (looks to be the same sig gen)

Manuals

Links

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[an error occurred while processing this directive] page created 26 Oct. 2001.