Wavetek 2520a 0.2-2,200MHz RF sig gen repair

[LogicalDave]

Tantalum caps need significant voltage derating; using 25V rated tantalums on an 18V line is a formula for long term failure.
Most manufacturers' rule of thumb for tantalums is to de-rate the voltage 50%, especially for MnO2 cathode tantalums.

It sounds like it is worth staying away from these older sig-gens unless you're ready to re-cap them; thanks for sharing
the detailed info; I was considering buying one and will probably now pass.

Some good white papers
https://sh.kemet.com/Lists/TechnicalArticles/Attachments/25/Derating_differences_Ta_KO_AO.pdf:
https://nepp.nasa.gov/files/24745/2013_n240_Teverovsky_ESTEC_Derating_paper.pdf
https://www.avx.com/docs/techinfo/VoltageDeratingRulesforSolidTantalumandNiobiumCapacitors.pdf

[AndreH]

Hi all
I too have the Wavetek 2510 (.2 - 1100MHz)
I managed to invoke the auto calibration, but I don't understand the selections 10, 12, and especially 18. When I select 18, I receive error on codes LVL, UVU, which I don't quite understand since I don't have the manuals. I can get the instrument to go past its self check startup sequence and it then works fine, but I have to virtually 'kickstart' the instrument to get it to work.

[AndreH]

Hi all
I too have the Wavetek 2510 (.2 - 1100MHz)
I managed to invoke the auto calibration, but I don't understand the selections 10, 12, and especially 18. When I select 18, I receive error on codes LVL, UVU, which I don't quite understand since I don't have the manuals. I can get the instrument to go past its self check startup sequence and it then works fine, but I have to virtually 'kickstart' the instrument to get it to work.

[dazz1]

Hi all
I too have the Wavetek 2510 (.2 - 1100MHz)
I managed to invoke the auto calibration, but I don't understand the selections 10, 12, and especially 18. When I select 18, I receive error on codes LVL, UVU, which I don't quite understand since I don't have the manuals. I can get the instrument to go past its self check startup sequence and it then works fine, but I have to virtually 'kickstart' the instrument to get it to work.

Hi
You have a journey ahead of you.  Attached is the page from the manual explaining the purpose of the diagnostics routines.
Passing self-check at startup means not a lot.

Test 18 displays outputs from control loops.  If the outputs are out of range, you get error codes.  Chances are that you cannot complete a full calibration procedure to get the instrument within spec.  If you have followed this thread, you will know what you face.   

I cannot tell you to go to xxx component and replace that to solve your problems.  I can tell you:

• a operator and service manual are essential (too big to post or email)
• look for failed tantalums first
• take a copy of the nvram asap
• post a copy of the ROM and nvram contents for others that follow you (and I)

Almost everything in these instruments is replaceable, so it is likely that your faults can be fixed.

Good luck.

I am currently waiting for parts I need to build a nvram reader/writer.  I was hoping that the contents of the nvram would be created by the autocal procedure.  I was not quite right.  I suspect there is an undocumented keyboard entry command required to factory enable installed hardware features.    That would have allowed them to use the same nvram board to fit to any 2510 with any features installed.

[AndreH]

 Thanks Dazz1. I noticed the name Artek manuals and I immediately ordered a copy. I received both the OM and the SM and I look forward to resolving my issue.

On switch on the LCD display displays flashing 'gibberish' By accident I noticed when I touch pin 36 on the uP the generator begins ts startup sequence and the display normalizes. It then stops at code 22. After spinning the dial it then stops at code 80. After spinning the dial again it completes the sequence and the unit is ready for use.

Everything seems copacetic. Frequencies and levels are fine. It's just on switch on that I have this issue. Initially there were various frequencies from 200kHz to 1.1GHz that were totally out. As an example, when I dial in 10MHz the output shows 30Mhz etc. After loading the 'factory' setting everything was perfect. I removed the NVRAM and drilled a hole to the positive of the battery. Battery voltage on the NVRAM measures 3.157V. The NVRAM seems fine. I soldered a wire to this positive pin and will monitor this voltage over time.

Anyway, I'll see if I can determine the problem.

Best regards

Andre
South Africa

[dazz1]

Hi
I replaced my nvram with a modern equivalent, but I didn't pre-load it with the contents of the old nvram.  As a result, I lost a feature.

I suggest to remove the nvram and copy its contents, so when it fails, you can program its replacement.

The firmware on the ROMs is the one thing that definitely can't be 2nd sourced.  Closely behind that is specific contents of the nvram not regenerated by the diagnostics routines. 

[dazz1]

Hi
Progress on the repair of the Wavetek 2520 has stalled for months while I waited for hardware from China. 
The hardware and software were copied directly from https://sites.google.com/site/gogleoops/mega-nvram-prog.
The only tweak I made was to use a 28pin socket rather than a 40pin socket. 

I could have purchased a general purpose programmer, but I would never use it again.  I elected to make a single purpose nvRAM programmer based on an Arduino Mega board.  I doubt the nvRAM programmer will never be used again, but I expect the Arduino will find a useful place to be.

I also fitted an IC socket to the 6502 micro-processor board so I can remove/reprogram/replace the nvRAM if needed. 

I have successfully programmed the nvRAM but not yet installed and tried it.    I used an image from the original factory fitted nvRAM to copy across to the new DS1225 nvRAM.  The old factory fitted nvRAM battery was well past its expected life, so it is entirely possible that the original factory image is corrupted.    Fortunately the nvRAM records configuration and calibration data.  The firmware is now located in OTP EPROM to replace the factory fitted EPROM (UV erasable).

[dazz1]

Hi
First power-on test indicates that the repairs, including the programming of the nvram, are 100% successful.  I need to run full diagnostics and calibration to confirm, but it is looking good so far.

[dazz1]

Hi
OK so I still have at least one more fault.
I was able to get through all of the self-tests OK.  No errors.
I was able to calibrate the oscillators and output level control.

Further testing showed AM and FM modulation is not working.  It was, but not anymore.
The FM modulation sort of works, but there is a step change at a certain modulation frequency.
Enabling AM modulation does not produce side bands, but it does change the output level. 

The LCD display is showing what I would expect to see.   That indicates that the firmware is OK.  I haven't created a fault with the nvRAM.
The manual has a diagnostics section for modulation, so I will work through that.   


So, do I expect to need or use FM/AM modulation?  NO. 
Do I need to fix it for any other reason?  NO.
Am I going to fix it?? YES of course. 
It would just annoy me to know that it is broken when I know I can fix it. 

The block diagram, with annotated modulation signal flow, is attached.

[dazz1]

Hi
OK did some some fault finding today.  With the assistance of my trusted hairy assistant, I identified the problem as zero volts on the -15VDC supply to the circuits for AM/FM modulation.  The good news is that finding this fault shows the programmed nvRAM is working as it should.   

Previous experience shows this is most likely due to failed Tant caps.   When I went looking, my trusty assistant pointed out the toasty brown one in the picture.  Well at least I think he did.  Unfortunately, inspection of the circuit diagram showed that the toasted Tan cap was on the +15VDC supply. 

The time taken to lift and test Tant caps is about the same time as replacing it.  I have just gone out and purchased about 20 Tan Caps to replace the toasted +15V and all the -15V caps. 

Some of you might be thinking that I should go through and replace every Tant Cap.  I have considered that but there are well over 100 of them on the boards.  I have decided to replace them one supply at a time.  If one fails, I just replace all the Tant Caps on that supply.   As I learn more about this piece of kit, I can isolate faults relatively quickly.  I have long lost count of how many faults I have fixed, but it is a lot.   It is likely that as I replace more failed Tant caps, I will get to the point where there aren't many more to replace. 

As an aside, I now think it most likely that the options are coded into ROM, and not enabled by some secret value loaded into nvRAM.  This could be confirmed by looking at the 6502 code that handles front panel button presses.  If there is a secret combination of button presses, they will be found there.  This means investigating or modifying the Wavetek would require reverse engineering the 6502 code.  Something I will not be doing.

[dazz1]

Hi
I replaced all of the Tant caps on the -15V supply plus the toasted one on the +15V supply.  I didn't bother testing the removed caps, I just replaced them.  After recapping the -15V supply was restored to normal.  So that fixed at least two more faulty components.

Now I am doing functional checks.  The internal AM/FM modulation works fine.  I just had to adjust the modulated signal amplitude.

I connected an external AF sig gen to the modulation input and that doesn't work.  The signal disappears in the circuit somewhere.  Initial testing indicates the problem may be digital.  A DAC is used to adjust the modulation level from 0 to 100%.  This appears to be stuck on zero so the DAC blocks the modulation signal.   The DAC is driven by a register with all output pins = low, so the fault is probably not the DAC.   I need to do some more testing to identify the root cause.

[dazz1]

Hi
I did some functional testing today.  The aim being to check that everything is working.
All testing shown here was at 500MHz with a 0dBm output from the Wavetek 2520.
The input of the spectrum analyzer was fitted with a Minicircuits  10dB attenuator  to ensure a 50ohm load for the Wavetek output.   This will have the effect of raising the RF noise floor seen on the spectrum analyser.

The first image is a 500MHz CW signal looking from 0Hz to 2.1GHz
There is one chirp above the noise floor, just to the left of the 500MHz signal.
 

Zooming into the main signal at 500MHz with a 10kHz span.   


Looking more closely at the main output at 500MHz with a 1kHz span.
The first peaks either side of the main output will be offset by the closed loop frequencies for the frequency control circuits. 


The images are supposed to be inline expandable thumbnails, but they aren't.

[dazz1]

Hi
Here is a the Wavetek 2520 output with internal AM modulation active.
In theory, there should only two frequencies, one either side of the main output. 
The spectrum is messy but still useable.

Note that the Wavetek and spectrum analyser don't agree on the frequency by 640Hz.  I don't yet know which one is the most correct. 

[dazz1]

Hi
The FM internal modulation produces a nice clean output when the Wavetek is setup for wideband FM modulation.

[dazz1]

Hi
I have proved that the internal FM/AM modulation functions work as intended.
I still need to figure out why the external FM/AM modulation isn't working.

[dazz1]

Hi
As I feared, the root cause of the problem with the non-functional external FM/AM modulation traced back to the firmware.
It turns out that the order of going from one modulation to another is important.  The attached drawing shows the permitted sequential steps in green, and the ones that don't work in red.
I can go from Internal AM to Internal FM, but I can't go diagnonally from Internal AM to External FM.    So all the hardware symptoms I saw were due to a firmware "feature".

The Wavetek also has an option button for external phase modulation, but this button does nothing I can see and this oiption does not show up in the self test.  There is a test that shows the options installed.  Also the manual indicates phase modulation requires an additional PCB module, which is not present.

The front panel has a covered hole for an option for pulse modulation of the RF output.  It also needs added circuitry.  I definitely don't have this option fitted.

So the plan is to soak test the Wavetek 2520 tomorrow to try and flush out any latent defects before I put the covers back on.   Then over the coming weeks, I will try and get access to enough equipment to do a basic calibration, focusing on  crystal frequency reference and output level. 

I think I started this repair about a year ago.  I never expected to find so many faults in one piece of equipment.  It has been a challenge but I learned electronics at around the period this was designed and built, so it has a familiarity to it.  It has definitely been hand built.  The circuit boards are dated and signed by real people.  No stick-on labels here.  Unlike old HP gear, it looks like Wavetek didn't quite finish design and development before it went into production.    The optional modules are solder-in not plug-in, and probably needed to be factory fitted, including new EPROMs with updated/modified firmware.

[tautech]

I think I started this repair about a year ago. 

You did, maybe a little over a year and July last was when I came to Wellywood and stopped by with Defpoms programmer.
Never did I imagine it would take you this long to get to where you are however life has this habit in getting in the way of projects don't it !
Keep at it Daz !

[dazz1]

Hi
Last night, I ran the built-in calibration. This sets the range of each of the voltage controlled oscillators.   This calibration means the Wavetek can select an oscillator, then apply a frequency control voltage that is close to the required control voltage.  Any remaining error is eliminated by the closed loop frequency control system.

There is another test where the Wavetek RF output level is checked at 60 points across the frequency range. I used my Siglent SA to check the levels.    At each point, the RF level is adjusted to a 0dBm output to a resolution of 0.1dBm.  Between points the Wavetek interpolates the output level.  As a result, the output level should be stable across the entire frequency range in a way that would be difficult to achieve with traditional analogue control methods.

Today I left the Wavetek running as a short soak test to try to flush out any latent defects.
The test was carefully supervised by His Majesty, the Right Royal and Honourable Sir Fluffy who showed true dedication and stayed the entire day.

I am now ready to put the covers back on.

The final step is to see if I can get access to equipment that I can use to verify the output level across the frequency range, and to adjust the reference oscillator.

[dazz1]

Hi
So the Wavetek 2520 project to complete all the repairs and get it back to a fully operational state ended today.
RF Test Solutions at https://www.rftest.co.nz/ kindly helped me do a limited calibration with a range of test equipment I could only dream about.

I was able to tune the 10MHz oven controlled crystal oscillator to within 0.28Hz, which corresponds to a 60Hz error at 2.2GHz. 
I ran the built-in calibration procedure to adjust the output level from 200kH to 2.2GHz to within +/-0.1dB at 0dBm output.
So the Wavetek is probably better than factory, because way back in the 1990's they probably didn't have the quality of test equipment that I had access to today.

So thanks to the two Dave's at RF Test Solutions.  I couldn't really finish off this project without them.    It has been well over a year since I started and now I can move onto something different.  I have already.

Now that I have restored the Wavetek, I just need to find a reason to use it.  At present it is a solution looking for a problem.

[Jeff eelcr]

Looking at your PCB I see a burnt ? near reg IC left side Middle
Jeff
This was in responce to post 7 picture 3.

[dazz1]

Hi
IC121?

[Jeff eelcr]

Glad you got it going nice peice of equipment enjoy it.
Jeff

[Abel]

Hi Dazz1,
I left a PM with you; if you do not get it in your Inbox, please check your Spam, you never know...
Best regards
AB

[dazz1]

Hi Dazz1,
I left a PM with you; if you do not get it in your Inbox, please check your Spam, you never know...
Best regards
AB

PM received.

[dazz1]

Hi
The Wavetek is backlit with a green electroluminescent (EL) panel that gives a nice even glow, but after about 35 years, it is looking a little weak so I started looking at options.  EL panels have a limited life which explains why the Wavetek has a switch on the back to turn the EL on/off.

Eventually I found 50cm x 3cm EL panels on Aliexpress.  I ordered the aqua colour because it is white when off.  It is also very close to the original EL colour.  I ordered it and fitted it.


It is very difficult to show how bright the new EL panel is but if you look carefully, the LCD contrast is relatively low.  Contrast improves with higher angle of view from slightly above.   The EL panel is almost too bright for the LCD, but not to the eye. 
Typical EL panels cannot be cut so I just left the surplus length to illuminate the interior of the enclosure.

Given that this was a one-for-one swap of new for old, this was a very easy mod.

The new EL panel came with an inverter that only produces 67VAC.  The Wavetek inverter provides 90VAC, but the LCD polarizing film reduces the light output.    I also replaced the wiring the the EL panel because this looked suspiciously like copper clad aluminium.    This turns to powder after a while. 

So not only is the WaveTek working, it now looks very cool with its new blue backlight.  As an added bonus, I think the external phase modulation option has started working after trying some GPIB commands.  I haven't tested it yet, but the button puts it into the correct mode.