Author Topic: Agilent E4421B RF generator restoration project  (Read 16617 times)

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Online nctnico

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Re: Agilent E4421B RF generator restoration project
« Reply #25 on: January 27, 2019, 11:13:18 pm »
My E4421B has thrown me a nasty curve ball today. It starts but when it gets to the splash screen I hear a loud click from one of the RF modules and it seems to reset into the splash screen. This cycle keeps continuing  :-BROKE Just as I wanted to make some measurements on my new HF differential probes.  :rant:  :rant: Just what I need. Maybe it is karma. A few days ago I have bought a different RF generator which hasn't arrived yet. Hopefully that is in a somewhat workable condition.
« Last Edit: January 27, 2019, 11:46:18 pm by nctnico »
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline Samogon

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Re: Agilent E4421B RF generator restoration project
« Reply #26 on: January 28, 2019, 12:38:00 am »
Looks 5V power rail has an issue, fail at load, making reboot cycle. That is first thing i would check.
Then if 5V ok, remove all boards except digital and check it
 

Online nctnico

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Re: Agilent E4421B RF generator restoration project
« Reply #27 on: January 28, 2019, 01:00:39 am »
The 5V looks ok with a DMM. I also see the diagnostic LEDs keep counting in a binary sequence. With all the RF modules removed the behaviour is the same. Maybe I need to try and reflow the SRAMs. There is a message about the RAM but it isn't clear if something is bad or not. It says:
Start = 0x300000
End =  0x3F9800
Errors =0x0

With the 'local' button pressed during power on, the E4421B won't start the firmware so the self test result stays on screen.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Online nctnico

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Re: Agilent E4421B RF generator restoration project
« Reply #28 on: January 29, 2019, 09:34:02 pm »
I made some progress. When it is cold and no RF modules are installed it will start succesfully. I tried using freeze spray but so far no joy.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline Samogon

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Re: Agilent E4421B RF generator restoration project
« Reply #29 on: January 29, 2019, 09:56:35 pm »
Thermal camera?
Measure cold and warm current consumption on 5V rail
 

Online nctnico

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Re: Agilent E4421B RF generator restoration project
« Reply #30 on: January 29, 2019, 10:16:48 pm »
I'm not so sure this is 5V related. I'd expect the system to do a full reset (go through the bootloader) when the power fails. Instead it seems the application crashes and restarts itself. Yes, I already re-seated all memory chips in sockets on the main board.

The chassis allows for a whole bunch of extra boards (which aren't in my machine) so my assumption is that the power supply has way more power than necessary. I won't rule the PSU out but using freeze spray on it hasn't solved the issue. It also doesn't smell like cat-wee which is a tell-tale sign of a bad electrolytic.
« Last Edit: January 29, 2019, 10:19:35 pm by nctnico »
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline TK

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Re: Agilent E4421B RF generator restoration project
« Reply #31 on: January 29, 2019, 11:37:24 pm »
There is a LED array indicating the status of the different power rails.  If all of them are ON, then the power supply is OK.  During boot, there is another LED array that indicates the boot step and once all tests pass, it counts up-down.  If it stops with a specific patter, then you can read the hex value and look at the service guide.
 

Online nctnico

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Re: Agilent E4421B RF generator restoration project
« Reply #32 on: January 30, 2019, 06:02:53 pm »
All the power leds are on and the status LEDs don't stop at a specific pattern. The bootloader and self tests are OK. It is the application itself which crashes. The status LEDs invert after the bootloader is finished and the left 4 (with the display towards you) are showing a binary counting pattern. When it starts OK then all the status LEDs are showing a counting pattern.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Online nctnico

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Re: Agilent E4421B RF generator restoration project
« Reply #33 on: January 31, 2019, 10:15:35 pm »
I found a rather large ripple on the 12V supply (200mVpp). The capacitors in the PSU still measured OK though and replacing them didn't help. I'm going to sell the generator 'for parts'. With all the repairs I did on it and the hacked output amplifier it is not going to be worth much even if it works. I have a 'new' RF generator coming my way anyway.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline Samogon

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Re: Agilent E4421B RF generator restoration project
« Reply #34 on: February 01, 2019, 02:25:53 am »
This is not outcome we all expect 
 

Offline pquadrat

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Re: Agilent E4421B RF generator restoration project
« Reply #35 on: February 08, 2019, 07:15:09 pm »
This thread is old but I think it is worth keeping any repair hints together.

Recently I acquired this signal generator and had missing columns on the bottom half of the LCD.  After replacing the LCD, the problem persisted.  While trying to map the LCD pins to the correct part on the motherboard, I used a continuity meter to map the pins.  It shorted one or both HM628512BLFP-7 SRAM chips (I think they are called BootROM RAM) and the motherboard did not want to boot, resetting every 3 seconds due to the power supply being shorted.  I then realized that the motherboard has a 3V lithium battery to keep some configuration alive and I passed the test probes over pins while they were powered by the Battery.  When I removed the SRAM chips, the board was back alive, but stopped with LED diagnostic code 2, and the manual says it is checking for BootRAM RAM, which of course were removed.  After soldering new SRAM chips, the motherboard booted correctly passing all the self diagnostics.  The LCD problem is still there, and I traced the problem to the Video RAM (HM514260CJ6) next to the Chips F65510 VGA controller (The controller seems to be OK because I can measure signals changing on all 8 bits that goes to the LCD).  I am waiting for the Video RAM chip to arrive and I will post the results

I bought the ESG mainboard from TK on ebay, to repair it. There were some more problems, most of them were easy to fix. One switching voltage regulator was shortet, and two transistors (display and green power LED) were shot.
But the lines in the display were still there.
After analyzing the protocol of the data transfer to the display, I was short before taking my logic analyzer. I even replaced the RAM chip a second time. But then I did some testing with removing signals to the display, and pulling the 8 lines to H one at a time. No result on bit 8.

Problem was a bent contact in the connector of the board to the LCD display! Looking back, it was obvious, because there came no signal for these lines out of the board. With black screen, alll signals were constant L. Pulling one of the 8 bits H there were white lines. But not on bit 8. It just had no contact to the display. But I was also sure that the problem came from the display controller or a bad display RAM chip. Key to the solution was to understand the display transfer protocol, which explained whyonly the lower half of the display was faulty.
 
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Offline TK

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Re: Agilent E4421B RF generator restoration project
« Reply #36 on: February 09, 2019, 04:10:15 am »
This thread is old but I think it is worth keeping any repair hints together.

Recently I acquired this signal generator and had missing columns on the bottom half of the LCD.  After replacing the LCD, the problem persisted.  While trying to map the LCD pins to the correct part on the motherboard, I used a continuity meter to map the pins.  It shorted one or both HM628512BLFP-7 SRAM chips (I think they are called BootROM RAM) and the motherboard did not want to boot, resetting every 3 seconds due to the power supply being shorted.  I then realized that the motherboard has a 3V lithium battery to keep some configuration alive and I passed the test probes over pins while they were powered by the Battery.  When I removed the SRAM chips, the board was back alive, but stopped with LED diagnostic code 2, and the manual says it is checking for BootRAM RAM, which of course were removed.  After soldering new SRAM chips, the motherboard booted correctly passing all the self diagnostics.  The LCD problem is still there, and I traced the problem to the Video RAM (HM514260CJ6) next to the Chips F65510 VGA controller (The controller seems to be OK because I can measure signals changing on all 8 bits that goes to the LCD).  I am waiting for the Video RAM chip to arrive and I will post the results

I bought the ESG mainboard from TK on ebay, to repair it. There were some more problems, most of them were easy to fix. One switching voltage regulator was shortet, and two transistors (display and green power LED) were shot.
But the lines in the display were still there.
After analyzing the protocol of the data transfer to the display, I was short before taking my logic analyzer. I even replaced the RAM chip a second time. But then I did some testing with removing signals to the display, and pulling the 8 lines to H one at a time. No result on bit 8.

Problem was a bent contact in the connector of the board to the LCD display! Looking back, it was obvious, because there came no signal for these lines out of the board. With black screen, alll signals were constant L. Pulling one of the 8 bits H there were white lines. But not on bit 8. It just had no contact to the display. But I was also sure that the problem came from the display controller or a bad display RAM chip. Key to the solution was to understand the display transfer protocol, which explained whyonly the lower half of the display was faulty.
I am glad you found the problem with the board and the display is now working.  Thanks for the follow up.
 


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