| Electronics > Repair |
| E4407B Tracking Generator Repair |
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| smgvbest:
--- Quote from: analogRF on October 20, 2020, 01:36:04 pm --- --- Quote from: smgvbest on October 20, 2020, 01:25:49 pm --- --- Quote from: analogRF on October 20, 2020, 12:30:15 pm --- --- Quote from: smgvbest on October 20, 2020, 12:27:37 pm ---Here's another part I'm having trouble finding Marking is a Linear Technologies 531 (LT531) but I can find no such beast. Anyone recognize this 8 pin guy? --- End quote --- 531 is the date code (2005/ week 31) This is LT1021 precision reference 10.000V --- End quote --- Thank you very much. That would make sense where it is in the circuit. i don't see how how to get from the marking 2110 i guess to a LT1021, is this some vodoo magic or am I (very likely) missing something simple)? --- End quote --- I already knew that part because I had seen and used it before myself but if you search for Linear Technology 2110 SOIC you'll find it after a little while ;) --- End quote --- Yeh, like the first result returned. oye Thanks again still working on reversing the control board (A2A2-BITG) Making progress slowly. Don't know how many layers this board is but its' more than 2 |
| smgvbest:
Just a quick update. while reversing the board. I decided to go ahead and replace the H346 on the RF board. while this did not fix the issue it did have an impact on the output the dB steps are now much more visiable and it much more consistent. for every 6db (1-6) on the H346 its unlevel then for 2db (7-8) it's level. this is now consistent all the way down to -66db (limit of the TG). I also pulled the 2 zenners to check out of circuit. they are 5v zeners and working ok I also pulle Q1 an tested it out of circuit. this is a LS312 Dual NPN transistor. one Transistor has a hfe of 285 the other of 108. I had ordered 2 LS312s just in case and the new ones are hfe of 276 and 277 so I'm going to replace Q1. Next. I pulled all 5 trimming pots and inspected them R2/R3 have been messed with PWR_LVL goes into R3 before going to U7 TL074 and the other input of this opamp (+12,-13 and out14) is the output of the peak detector. this then goes to ALC_MON and thru R4 to U5 which controls V2. R5 looks to set the reference for one opamp on U5. U5 other opamp handles V1 which uses R1 and R2. just for reference I'm attaching a image of the board with the trimmers and Q1 removed. I also did record the settings for each Pot (R1-R5) just in case NOTE: replacing Q1 had no noticeable effect |
| analogRF:
--- Quote from: smgvbest on October 25, 2020, 03:40:01 am ---Just a quick update. while reversing the board. I decided to go ahead and replace the H346 on the RF board. while this did not fix the issue it did have an impact on the output the dB steps are now much more visiable and it much more consistent. for every 6db (1-6) on the H346 its unlevel then for 2db (7-8) it's level. this is now consistent all the way down to -66db (limit of the TG). I also pulled the 2 zenners to check out of circuit. they are 5v zeners and working ok I also pulle Q1 an tested it out of circuit. this is a LS312 Dual NPN transistor. one Transistor has a hfe of 285 the other of 108. I had ordered 2 LS312s just in case and the new ones are hfe of 276 and 277 so I'm going to replace Q1. Next. I pulled all 5 trimming pots and inspected them R2/R3 have been messed with PWR_LVL goes into R3 before going to U7 TL074 and the other input of this opamp (+12,-13 and out14) is the output of the peak detector. this then goes to ALC_MON and thru R4 to U5 which controls V2. R5 looks to set the reference for one opamp on U5. U5 other opamp handles V1 which uses R1 and R2. just for reference I'm attaching a image of the board with the trimmers and Q1 removed. I also did record the settings for each Pot (R1-R5) just in case NOTE: replacing Q1 had no noticeable effect --- End quote --- I would never start replacing components at random for no reason unless there is evidence it is not working. Not only this will not achieve anything and waste a lot of time you end up tampering with the calibration of instrument. Q1 was already tested fine, so no surprise there. and why did you take out all the potentiometers? if you are sure R2/R3 have been messed with and PWR_LVL and peak detector are related to them, that's your clue! :) that could very well be the cause of your problem because so far there does not seem to be any defective component anywhere. i would like to see a schematic of that board (not the RF section which is quite clear already) |
| smgvbest:
I did not replace randomly anything H346 when looking at it the RF IN was at -60db after the filter and into the H346. without the H346 it was at about -10db. I replaced it because it appeared to be pulling down the RFin Q1 is a matched pair of NPN transistors HFE's that different are not matched. which is why I pull it and replaced it. the Pots where pulled to inspect out of circuit due to tampering. They did not remove the silistic on the adjustment screw and where visibly damaged. I wanted to be sure they were ok and while out I got a good read on how they where set. as well as a pic of the board. I've hand drawn it in various parts. I'm now putting it all together and will verify it against the board then plan to post when it's done |
| analogRF:
--- Quote from: smgvbest on October 27, 2020, 03:59:53 pm ---I did not replace randomly anything H346 when looking at it the RF IN was at -60db after the filter and into the H346. without the H346 it was at about -10db. I replaced it because it appeared to be pulling down the RFin --- End quote --- how did you measure the 3.92GHz signal at the RF pin of HMC346? how much was the output amplitude? it is critical how you measure it and besides when you leave that open circuit (by removing the chip) that changes the whole dynamics...it will be a totally different reading of course.... |
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