| Electronics > Repair |
| Agilent E4421B RF generator restoration project |
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| Mosaic:
I got an E4432B ESG-D, OPT 100,1E5,UN8,UN9,UNA,UND for abt $590 on Ebay auction with an unleveled error. After much hunting I realized that the burst mod drive on the A9 output board (E4400-60003) was not responding and causing the BURST MOD to be at 0% duty = no signal. W/o a schematic I cannot resolve this...although the problem is located. Too many buried vias etc. in a multilayer board. I am unable to rev. eng. a schematic. So, in order to get the unit alive, albeit without burst modulation, I did a hack. I fed the ALC MOD 8V PIN diode drive forward over the U180 mmic via a 20K resistor to create a BURST MOD 100% duty drive. Smaller resistor values caused the U180 to have +ve feedback causing unleveled errors due to too much signal strength. A 1K? pushed it up over 10dBm! Here is a pic of the solution which works across the full 3Ghz span. AM & FM modulation etc. are fine. |
| Mosaic:
Something interesting. The burst mod appears to be working with the hack in place. Feeding a waveform into the EXT1 input and activating the burst envelope results in modulation. Not linear though. A 2Vpp sine wave modulation signal results in a +4dBm to -7dBm modulation of the carrier.Sine wave appears a bit top flattened. Internal AM modulation shows a good linear sinewave modulation. :) Pulse modulation is also good. :-+ The zero span view of the sine wave burst mod RF out on my DSA implies a LOG sine wave modulation. Since I have a UN8/9 and UND option...it appears that the burst envelope IS indeed handled as a LOG signal, with the AM envelope being linear. :) Thus, the single resistor, pull up, hack may have done the trick altogether! :-+ |
| nctnico:
Perhaps it could be caused by a problem on the board driving the burst modulation. In my E4421B there was a power supply absent in one of the other modules because there was a blob of solder shorting the supply rails. |
| Mosaic:
Yes, that's so. But w/o a decent schematic or even a block schematic of the UN8 gen, I'd not spend time hunting a bad solder joint or such like as the solution in place seems good. All voltages on the system show good. Interestingly there are two units almost identical to mine with identical failure modes on Ebay now. Could be a good deal if the problem is the same. #262509365736 #252448189801 If I were in the Con US I'd be tempted to repair and resell them given their option load out. |
| Samogon:
--- Quote from: Mosaic on September 07, 2016, 12:12:03 am ---Yes, that's so. But w/o a decent schematic or even a block schematic of the UN8 gen, I'd not spend time hunting a bad solder joint or such like as the solution in place seems good. All voltages on the system show good. Interestingly there are two units almost identical to mine with identical failure modes on Ebay now. Could be a good deal if the problem is the same. #262509365736 #252448189801 If I were in the Con US I'd be tempted to repair and resell them given their option load out. --- End quote --- Nothing said about failures on this items. No error listings. May be i miss something? |
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