Agilent E4421B RF generator restoration project - Page 1
Forum section: electronics / repair

author: nctnico
author_rank: Super Contributor
timestamp: December 27, 2014, 03:31:33 pm
content: About a year ago I bought a 'for parts' E4421B from Ebay. The most common fault I found when researching these machines is the output amplifier going bad. I more or less assumed this machine was most likely to have the same problem. -Spoiler alert- I was wrongThe most obvious problem was the display. Did someone stick a post-it behind it? After some reading I discovered these DSTN screens can also create a yellow color when overdriven.After opening it up I got a bad feeling. Everyone who has worked at a repair shop knows the look of a test unit. The unit with the boards which can't be fixed but are good enough for experiments or to try something quickly. Every module has a blue cross on the outside... To sum up the problems with my E4421B:Frequency slightly offOutput level too low and distortedDisplay not workingNo AM modulationDead backup batteryThe first thing I attacked was the frequency problem. According to the service manual (which only has block diagrams and no schematics) the reference board should be the place to look for that problem.

author: nctnico
author_rank: Super Contributor
timestamp: December 27, 2014, 03:43:41 pm
content: The reference boardThe reference board generates the reference frequency and a 1GHz signal which is used on the output board to generate frequencies in the range from 100kHz to 250MHz. The AM and FM modulator are also on this board.After opening the reference module it quickly becomes clear a chip labelled U13 is missingThat is about the worst that can happen when trying to repair something without a diagram. Oh crap...Some probing around learns me that the missing chip is connected to the reference input of a DAC (circled in red) which seems to have been replaced given the later production date than the other chips and lots of flux residu. So U13 must be some kind of reference.Fortunately Mike (Mikeselectricsstuff) did a teardown and he took a closeup of the chip:Some Googling for a Linear Technology device labelled 2110 revealed it is an LT1021 10V precision reference. Let's order one but first see why it was removed. I hooked up some wiring to supply 10V from a bench PSU and measured the current:It shows more than 11mA is drawn from the reference chip. Since the maximum current is 10mA it is no wonder why the reference chip was removed. With the bench power supply set to 10V the output frequency is spot on though. I tried to find other loads connected to the LT1021 but the circuit gets fuzzy quickly. Now how to proceed?? Since the reference can source and sink current I decided to live with the 11mA and added a 470 Ohm bypass resistor from the input to the output (this is a suggestion from the LT1021 datasheet). This should limit the current through the LT1021 to around 5mA.I suspect the AM modulation not working could have something to do with the high current draw on the reference but I think I just leave that.I declare the reference board 'fixed' for now.

author: G0HZU
author_rank: Super Contributor
timestamp: December 27, 2014, 04:39:31 pm
content: Interesting threadIt's a shame that HP/Agilent/KS won't release schematics of these old signal generators. They do seem to be suffering from various reliability issues and I'm not sure I envy your task in terms of repairing your list of faults...QuoteIn case you don't already know this, the AM often comes for free on a sig gen that uses ALC to keep tight control on the RF output level. This is because the AM modulation is often injected into the ALC system as a modulated reference for the ALC to aim for and track. So as long as the ALC response time is faster than the AM modulation then the ALC will track and AM modulate the RF output faithfully.So if the levelling is faulty then I'd expect the AM to be faulty too. But I don't have any experience of working inside these E44xx series generators even though I own a couple of them. So maybe this doesn't apply.What I will say is that these aren't really lab grade generators in terms of AM modulation quality. So don't expect too much in terms of low distortion if you dial up AM modulation from the menus after you repair it. Both of my E44xx generators are quite poor in this respect.

author: KJDS
author_rank: Super Contributor
timestamp: December 27, 2014, 05:57:46 pm
content: I've recently found a couple of dead units in the back of my storage lot. One has a label on it saying "display broke". No information on the other so I've just tested it and the display works but it looks like it has a lot of other faults on it.

author: nctnico
author_rank: Super Contributor
timestamp: December 27, 2014, 07:40:21 pm
content: The output boardThe picture below shows the output board and the signal paths (0.1 to 250MHz in blue, 250MHz to 3GHz in purple). There is a lot going on here. Besides the end amplifier this board also contains the filters to filter unwanted harmonics from the output signal and the auto-level circuitry.The big giveaway was the blue cross on the end amplifier (1GMI-420). Ofcourse this chip is unobtanium so I had to somehow replace it. The first thing I tried was to replace is with a wire between the input and output. This gave some signal but at very low (and distorted) levels. I needed something stronger so I made a small board with an ADL5602 MMIC as an amplifier replacement.This gave me an idea on the amount of amplification needed. This little board had a major problem though: it sang like a bird due to the poor layout. From this board it became clear there was also something wrong with the auto leveling. After taking parts of the log-amp circuitry apart it became clear the detector diode (2 diodes in one package; blue circle) was broken as well. Fortunately there was a diode with the same markings on the board and even more surprisingly only one diode was used (red circle) and that diode wasn't the one that was broken in the detector diode. After swapping these over the automatic levelling started to show some signs of life.I did some measurements on the input and output levels of the amplifier and it appeared that a lot of harmonics at the output where produced because the input signal was already overdriven. This was especially true for the <250MHz range because the input signal is around 3dB lower. I guestimated the original amplifier had an amplification of at least 30dB. I was unable to find a low noise MMIC with that much amplification. I also needed a low noise (low noise figure) and low distortion (high IP3) part. I decided to cascade 2 MMICs with a gain of around 15dB each. I choose the Triquint TQP3M9028 devices because of their low noise and low distortion figures. A problem with MMICs is that they don't perform well at low frequencies which isn't surprise because their outputs are shorted to the power supply. I did a test with a resistor in series with the inductor and this greatly improved the low frequency performance. I had some PCBs made by Seeedstudio which have the same size as the original amplifier. The replacement PCB has two layers; the bottom layer is a solid ground plane.The attached PDF shows the schematic of the amplifier.I also found the root cause of the amplifier failing:The aluminium block it is mounted on has a very rough surface. This is extremely bad for heat transfer. I don't understand how HP/Agilent/Keysight managed to overlook this! If the aluminium block and the module housing where milled so the block and the housing had smooth surfaces the amplifier most probably wouldn't have died.Anyway, with this fix the output signal works over the entire range albeit with some distortion at the lower frequencies (100kHz to 5MHz). The maximum output level is about +3dBm (more between 250MHz and 2GHz) but that is good enough for me.

author: G0HZU
author_rank: Super Contributor
timestamp: December 27, 2014, 08:19:21 pm
content: I'm a bit confused because your output board looks like it has the IQ modulator on it. Is it the original board for this generator? It looks like an ESG-D board but I thought the E4421B was an ESG-A signal generator.I nearly spat my drink out when I saw your ADL5602 board. Definitely an oscillator with that layout

author: nctnico
author_rank: Super Contributor
timestamp: December 27, 2014, 09:20:56 pm
content: @G0HZU: Let's just say the board came with the generator. It's part number is E4400-60003. According to the service manual this can be used in both the ESG-A and ESG-D series.Time for short intermezzo:The attenuatorThese generator can come with either a relay based or an electronic attenuator. The attenuator can attenuate in steps of 5dB. So the output board has to regulate the signal between -5dBm and upwards. The problem with the relay based attenuator is that it can wear out. Fortunately my unit has the electronic attenuator. While searching for the cause of the weird output level behaviour I took the attenuator apart. Maybe I should not have done that but it resulted in some interesting pictures:The top side:The bottom side:There are a bunch of analog switches on the board and filtering, and filtering and more filtering. Also notice the 5 leds in the bottom left corner...When the attenuator is turned on they shine a red light to the inner of what is obviously the attenuator unit which needs some optical effect to work. Google told me nothing. If someone else knows what kind of technology is used here I'd be gratefull if he/she can share some information.

author: PA0PBZ
author_rank: Super Contributor
timestamp: December 27, 2014, 09:39:53 pm
content: Quote from: nctnico on December 27, 2014, 09:20:56 pmI took apart the attenuator of my E4433B because it was making strange steps, and I didn't notice any leds in there. And yes, it was the electronic one also. Turned out that there was some milling residue shorting out one of the signals, go figure...

author: Fraser
author_rank: Super Contributor
timestamp: December 27, 2014, 10:00:49 pm
content: A very interesting thread. Thank you. I shall continue to follow it with interest.The Output amplifier MMIC is available as a tested used part from China. I had a Google search some time ago.Aurora

author: nctnico
author_rank: Super Contributor
timestamp: December 27, 2014, 11:13:05 pm
content: The displayI took the display apart to see if it could be fixed but that wasn't the case. One of the driver chips obviously was broken. I quickly found a Chinese Ebay seller which claimed to have the display for $140 + $40 shipping. Including customs duties and taxes the display would add up to 180 euros. Because of the age of the equipment the display could be from a salvaged unit with lots of hours and a dim CFL backlight.I choose to apply my TFT conversion skills. I tracked down an 8" 800x480 screen (TX20D16VM2BAA) from Ebay which has almost the same size as the orginal screen. That left me with a bit of a problem; the original display has a resolution of 640x320. I need some scaling. Horizontal: 800/640=1.25 so I need 5 output pixels for 4 input pixels in the horizontal direction. Also the active area of the TFT screen is heigher than the original screen so I may need some stretching there as well.The new display mounted: Some 3M double sided tape and stick-on feet keep it firmly in place. To prevent shorts between the backplate and the controller board I stuck some polyimide tape on the backplate.The primary problem is to convert the data for the DSTN screen into information a TFT can work with. A DSTN screen is black/white and usually has 4 to 8 parallel data lines, a clock and vsynch+hsync signals. To complicate things more the pixels of a DSTN screen are typically 'modulated' to get grey scales. The more consecutive frames where a pixel is 'on' the whiter the pixel and vice versa. This means that a picture is spread in time over several frames. In the case of the E4421B the display has 8 bits and one picture is made up from 4 consecutive frames.What I need for the TFT screen is to count the number of ones for each pixel over a period of 4 input frames. That is not going to happen on the fly. The refreshrates are also too different for that. Time for a CPLD and SRAM. The TFT screen uses a pixel clock of 32MHz but I'm not going to store RGB data in the SRAM. All I need is the count of the number of ones; 4 bits is more than enough for that. If I use a 16 bit SRAM I can supply 4 pixels of TFT data with one read cycle. The TFT data can be converted to RGB by using a fixed pallette. All in all that leaves three 32MHz clock cycles to do something else or use slower memory. I choose to use slower (45ns) memory so I can use 2 clock cycles for reading TFT data and 2 clock cycles for dealing with the DSTN data. But... remember I need to stretch the TFT data so I'm using 5 clock cycles in total (which means one TFT pixel gets repeated). In total 2 clocks to read TFT data, 2 for DSTN data and 1 for nothing. This means that I have 32M/5= 6.4 million memory time slots for dealing with the DSTN data.The DSTN data is clocked at a rate of 2.1MHz -ish. I'm using the 32MHz clock to sample the edges of the dot clock, vsync and hsync. When a vsync arrives I reset the line counter and increment a frame counter. The hsync resets the dot counter and increments the line counter. The dot clock increments the dot counter. These counters can be combined into a memory address nicely. There is more than enough memory so no need to make things more complicated the necessary. The most complicated part is counting the number of ones over 4 frames. For each dot clock cycle it means reading the old value from RAM (or force the value to zero when dealing with the first frame), increment the value and store the value to RAM. So processing every DSTN pixel takes one read and one write cycle. That adds up to 4.2 million memory accesses per second. Since there are 6.4 million available memory bandwidth is not going to be a problem. Unfortunately there is a problem... The DSTN data is 8 bits wide. The first 4 bits are for the upper 160 pixels of the display, the second 4 bits are for the lower part. I can't process these in one go. I solved that by using 8 frames to produce one TFT screen display image. From the first 4 frames (1 to 4) the data from the upper 160 lines is used, the next 4 frames (5 to 8 ) are used to create the lower 160 lines. The last step is to use double-buffering to prevent the TFT screen showing how the pixels are counted. After 8 frames have been processed the display areas are swapped so the TFT screen shows steady data.I designed a small board and had it made by Seeedstudio. The CPLD is a Xilinx XC95144XL; the RAM is a 512kx16 45ns SRAM from Cypress. The CPLD is in a TQFP144 package. I ordered the wrong package for a different project so I opted to design the PCB so I could use that one. By optimising the connections between the RAM and the CPLD the PCB has most traces on the top layer which kept it very compact. The XC9500XL series is 5V tolerant and has internal flash. It is a much nicer solution than an FPGA for a project like this. The only external components are a 3.3V regulator and an oscilllator module.I also managed to source a connector which is the same as the connector on the original display. This means I can keep the existing display cable and don't need extra wires to the motherboard of the E4421B.After several hours of VHDL coding and getting the timing right things start to look good but I forgot the active area of the new display is higher than the original display so stretching 320 lines into 480 lines isn't going to cut it:After some fiddling the height is just right:The fixed pallette conversion allows any color scheme. Who's afraid of red, yellow and blue?

author: nctnico
author_rank: Super Contributor
timestamp: December 27, 2014, 11:37:58 pm
content: Quote from: Aurora on December 27, 2014, 10:00:49 pmAny pointers to a reputable seller? The output amplifier is definitely a key part of getting a clean output signal. I have seen them as well but mostly as part of a board which was cut from an output board.

author: tautech
author_rank: Super Contributor
timestamp: December 27, 2014, 11:42:18 pm
content: Wonderful work.QuoteNa keep it white on blue.

author: nctnico
author_rank: Super Contributor
timestamp: December 27, 2014, 11:49:22 pm
content: ConclusionAll in all the generator isworkinguseful again except for AM and probably FM modulation as well. Both these modulations are generated on the reference board so there still are some problems lurking in there. My primary use for this generator is tinkering / learning HF stuff and that usually involves sending sine waves through amplifiers and/or filters.Yes, I also changed the battery but that was an easy job.

author: nctnico
author_rank: Super Contributor
timestamp: December 28, 2014, 03:50:16 pm
content: Fixing modulationI couldn't resist taking another look at why the modulation wasn't working. First I tried to apply an external modulation signal to make sure the internal modulation signal generator on the motherboard wasn't the problem (according to the service manual the internal modulation signal is generated on the motherboard). The modulation also didn't work with an external signal so the cause of the problem must be somewhere on the reference board. So I opened the reference module again and I noticed a few opamps where running hot. Both these opamps where connected to different DACs. DACs are prone to failure in general but two broken DACs is still unlikely. I tried to find out what the opamps had in common and I ended up with the power supply (+15V and -15V). I could trace the +15V back to the power supply connector but I could not find -15V. I remembered that the board had a blob of solder when I got it (inside the red circle):I removed it hoping it would not be harmful but appearantly it shorted -15V to ground which burned a filter inductor. I replaced it with a ferrite bead and presto: FM and AM modulation working again!The hot opamps are circled in green, the removed solder blob in the red circle and the replacement ferrite bead in the blue circle. And yes, I removed the resistor across the 10V reference. I didn't measure the current but I doubt it will be needed.

author: G0HZU
author_rank: Super Contributor
timestamp: December 29, 2014, 05:21:16 pm
content: QuoteInteresting... On Mike's youtube teardown his HP4421B A had the areas for the IQ modulator blanked off in the artwork and replaced with a stripline section to bypass this unused area. So he has a different output board. So maybe HP/Agilent decided at some point to use the E4400-60003 output board (with IQ modulator) on both A and D models?In my opinion the IQ modulator is one of the best features of this generator series. I wonder how much extra work it would be to make use of your IQ modulator?That was impressive work on the screen replacement by the way

author: Mosaic
author_rank: Regular Contributor
timestamp: September 05, 2016, 04:42:09 am
content: 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.

author: Mosaic
author_rank: Regular Contributor
timestamp: September 06, 2016, 09:15:46 pm
content: 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!

author: nctnico
author_rank: Super Contributor
timestamp: September 06, 2016, 11:44:36 pm
content: 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.

author: Mosaic
author_rank: Regular Contributor
timestamp: September 07, 2016, 12:12:03 am
content: 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#252448189801If I were in the Con US I'd be tempted to repair and resell them given their option load out.

author: Samogon
author_rank: Frequent Contributor
timestamp: September 08, 2016, 04:35:54 am
content: Quote from: Mosaic on September 07, 2016, 12:12:03 amNothing said about failures on this items. No error listings. May be i miss something?

author: Mosaic
author_rank: Regular Contributor
timestamp: September 08, 2016, 05:31:43 am
content: This one: 252448189801 specifies no RF and unlevel error...which precisely matches what I had.I'd suggest that if you're interested that you ask for verification that the coherent output is alive, which then means the A9 board is the fault as mine was.The other says dual arb error which is the UND option, which can be removed. But may be a voltage issue which makes it an easier fix.

author: Samogon
author_rank: Frequent Contributor
timestamp: September 08, 2016, 05:45:28 am
content: Oh i must be blind, reading description carefully explains errors. Sorry

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: November 01, 2017, 02:33:09 pm
content: Just a heads up...I followed the fix shown above adding the 20k resistor, also touched up several questionable soldered areas in that circuit. Voila! works great. Then I said to myself, remove the resistor to prove that fixed it, not the touch-up soldering. Removed the 20K resistor. Voila! Still working fine! Chances seem good there are issues with solder, not circuit values (at least with this E4432B).

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: November 03, 2017, 02:19:42 pm
content: Had this E4432B running about 36 hrs. w/no problems. One of our engineers took it away to his lab, and used it under load for about 4-5 hours, then brought it back complaining "it's broke". Noticed the supply for the output amp IC was shorted to ground, then noticed all the pins were shorted to it's integral heatsink/mounting. Noticed one of the screws for mounting was loose. Looks like this is another fried 1GM14201 because of poor heatsinking, and mounting. Thanks Agilent!

author: TK
author_rank: Super Contributor
timestamp: September 25, 2018, 12:27:56 pm
content: 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

author: nctnico
author_rank: Super Contributor
timestamp: January 27, 2019, 11:13:18 pm
content: 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 continuingJust as I wanted to make some measurements on my new HF differential probes.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.

author: Samogon
author_rank: Frequent Contributor
timestamp: January 28, 2019, 12:38:00 am
content: 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

author: nctnico
author_rank: Super Contributor
timestamp: January 28, 2019, 01:00:39 am
content: 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 = 0x300000End = 0x3F9800Errors =0x0With the 'local' button pressed during power on, the E4421B won't start the firmware so the self test result stays on screen.

author: nctnico
author_rank: Super Contributor
timestamp: January 29, 2019, 09:34:02 pm
content: 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.

author: Samogon
author_rank: Frequent Contributor
timestamp: January 29, 2019, 09:56:35 pm
content: Thermal camera?Measure cold and warm current consumption on 5V rail

author: nctnico
author_rank: Super Contributor
timestamp: January 29, 2019, 10:16:48 pm
content: 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.

author: TK
author_rank: Super Contributor
timestamp: January 29, 2019, 11:37:24 pm
content: 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.

author: nctnico
author_rank: Super Contributor
timestamp: January 30, 2019, 06:02:53 pm
content: 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.

author: nctnico
author_rank: Super Contributor
timestamp: January 31, 2019, 10:15:35 pm
content: 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.

author: Samogon
author_rank: Frequent Contributor
timestamp: February 01, 2019, 02:25:53 am
content: This is not outcome we all expect

author: pquadrat
author_rank: Regular Contributor
timestamp: February 08, 2019, 07:15:09 pm
content: Quote from: TK on September 25, 2018, 12:27:56 pmI 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.

author: TK
author_rank: Super Contributor
timestamp: February 09, 2019, 04:10:15 am
content: Quote from: pquadrat on February 08, 2019, 07:15:09 pmI am glad you found the problem with the board and the display is now working. Thanks for the follow up.

author: minsik
author_rank: Contributor
timestamp: March 18, 2024, 10:16:44 pm
content: New (second hand) E4421B arrived and was told it "works good" by reputable dealer. Not so, the reference is faulty, being too high in frequency by about 200-300 hz as well as the external Ref says its unlocked! Damm.Went whole hog in testing in stages and finally tracked down to the 10Mhz TCXO diagnosed as faulty. Dismantled and added a 1.5pf across xtal to tune. Reassembled and tested A1 and external ref now works 100.Free run testing and the 10Mhz does vary about 3-5hz over cold to hot conditions. At least external Ref is fully operational at all times.Problem solvered!Unit destined for a fishing sinker is now pride of place in workshop.

author: nctnico
author_rank: Super Contributor
timestamp: March 18, 2024, 11:42:29 pm
content: This is the link to Mike's ( Mikeselectricsstuff ) teardown video (as requested per PM):Nice find! I guess the output amplifier is still working? This was the biggest headache for the unit I used to own.

author: minsik
author_rank: Contributor
timestamp: March 20, 2024, 12:33:20 am
content: Thanks nctnico.I am very pleased with the outcome, a working E4421B! In my dreams I did not think to get this magnificent generator for so little money (relatively speaking)!Yes all levels and all frequencies appear excellent as measured on a Siglent spec-an + FA-3 counter. This thing is beastly good. it reeks quality. So far its life was 34,400 approx hours, 200 power cycles, with lcd being on for 100% of the time. It must have been in a factory or long running in an assembly line or similar. I have turned on screen "light and text saver" and see a difference slowly coming. Even then LCD and backlight is good, maybe a slight yellowing.I was able to win an eBay replacement reference module (same as mine, basic xtal unit) that is on the way. So I can see if that is better or worse from my doctored one when it arrives. Also then it might allow some experimenting with changing the xtal to a OCXO. CCT seems to be able to cope with many differing mountings and types, sine-square etc. Only thing is if xtal is oven controlled I am not sure how it will react without enabling the "oven cold cct" (5 minute timer) in software, as I don't have any confidence/knowledge (treading carefully) in any software changing, yet!Very chuffed I got a working good generator.On any repair, "Never give up, never surrender! (Galaxy Quest)".Minsik.Edit update 10/2025.Replacement reference looks like new old stock in original factory parts box. works a treat and reference adjustment when warm is pretty well spot in the middle values for adjusting the free run of this reference pcb. Amazing the original reference module i added the cap to the 10Mhz xtal, also works well, has a wider range with temperature but always locks cold and hot too. Win win.This thing just runs and runs. I did upgrade the software from B.03.50 to B.03.86 (the final version I believe). Serial at 9600 board takes about an hour! Siggen+laptop on a UPS, no screen saver etc. Reason to change was evident in looking at the board info inside the unit on the original software, it was intermittent reading the boards data, but on the latest software it is 100% repeatable. Maybe there was another problem like intermittent attenuator up down control, but not 100% sure (old brain!)One other problem that crept in late last year 2024, I had was some intermittent mechanical attenuator operation, all random, and frustrating! So getting ready to replace the plunger orings, (kit on hand = common problem) I found they were 100% good condition and no need to replace even after 8.6 million switches! However the gold plated glass attenuator modules / each step 10/20/40 DB units, were cleaned and cleaned and still the problem just kept getting worse and worse. Taking life and limb in hand after microscope checking, I performed religious sacrilege, anti my whole life teaching about such things, but with nothing left to lose I did this. Used my multimeter home made probe containing a sewing machine needle, created a series of light scrapes diagonally one way, then another, creating a criss cross pattern in the (whatever was the oxidisation layer) over the gold plating. Assembled and tested and viola, I actually cried from relief, it has worked 100% since that time 1 year ago even with a lot of use, 120% perfect. Totally repeatable, totally reliable. Just shows never give up!

author: imaurente
author_rank: Contributor
timestamp: April 16, 2024, 06:29:03 pm
content: Hey guys!I'm having problems with my 4421B, it simply doesn't activate the modulation, I hear the sound from the relay, but it doesn't work. It's like trying to activate modulation, but it doesn't, I've already done some tests:1) I used the external modulation input and it worked well;2) The OCXO is in order, 10mhz perfect and signal without imperfections.One detail, about a year ago, my time base stopped working and I replaced it with the same one (ebay) and everything went back to normal, I don't have the service manual, if someone could make it available it would be of great help.Note: The signal in blue and the attempt to modulate in FM (dev=100khz)Hug!

author: e120guru
author_rank: Newbie
timestamp: December 15, 2024, 06:51:04 pm
content: @nctnico, do you by any chance still have your design laying around for the display interface? Or any details on the pinout of the original display cable? I need to perform a similar operation, and managed to come accross the same display you used.