Wiltron 6409 RF Scaler Network Analyser

[dazz1]

Hi
I am now the owner of a Wiltron 6409 Scalar Network Analyser.  A classic obsolete item of test equipment.  Most manufacturers stopped making/selling SNA around 2018 because about that time VNAs were cheaper to make and sell.  As far as I am aware, you can't buy a new SNA anymore.

In the mid 1980's, a 2GHz SNA was a serious piece of kit.  This 6409 was purchased by Radio New Zealand (RNZ) some time after 1985 (the date on the power supply PCB) and Nov 1989 (the date the manual was updated).  I found a brochure with prices here:    https://testequipment.center/Product_Documents/17065_7A5FE300.pdf

It would have been purchased for the princely price of $USD12,900 plus $USD2,100 accessories.  A total of $USD15,000, equivalent to $NZD25,500 in 1987.    When that value is adjusted for inflation, it is equivalent to $NZD71,000 today.    That figure excludes shipping costs, local agent commission, and import tax applicable in the 1980s.  The Wiltron 6409 probably cost RNZ around $NZD100,000 to $NZD200,000 total in todays money.  It was a serious investment in very cool technology.    Now, 40 years later, it is e-waste unless someone like me rescues it.  I even paid some money for it.

The 6409 has probably been in storage for a long time, so I took the usual precautions to ease it back to life.     When I restored low voltage power, a couple of tantalum caps released the magic smoke. 
In addition, the CRT displayed readable text, but mixed with a pattern (no photo yet).  That will be a challenge to repair.

The $2,100 accessories were all RF adapters that suffered in storage after the foam packing disintegrated and held moisture.  It would cost a lot more than $2,100 to replace these components now so I will probably get some cheap Chinese versions.

[dazz1]

Hi
The 6409 is now withholding the magic smoke.
I can now address the displayed image problem.  A series of dots overlaid on the text.
The buttons are responding correctly. 

The mains powered fan is making a lot of bearing noise. 

The graphics on the front panel are disintegrating.  I really need to find a donor 6409 but there is absolutely no danger of finding one here. E-bay prices are at fantasy levels.

[ve2ulu]

I have two 6407 or 6409, i dont remember...  in working condition!
6407 is 1GHz and the 6409 is 2GHz
Is a 8088 cpu inside, i play with rom to see my name at the boot screen....
Some think corrupt the data bus and make bizarre screen.

5vdc is good and no ripple?
The screw on pcb is big capacitor, check the ripple.
No sign of corrosion on pcb?
Backup battery on CPU leak?

Remove card, clean the gold contact on the edge connector with pen eraser (rubber eraser)

juste in case...
https://fr.scribd.com/document/480870160/Wiltron-6409-service-user-ID6266-pdf

[dazz1]

I have two 6407 or 6409, i dont remember...  in working condition!
6407 is 1GHz and the 6409 is 2GHz
Is a 8088 cpu inside, i play with rom to see my name at the boot screen....

Cool, how did you do that?

Some think corrupt the data bus and make bizarre screen.

According to the manual there are 3 graphics planes in 3 separate memory banks.  I think two are working and the third plane is displaying random values.
The 6409 appears to be functioning correctly.  All the buttons do something.

5vdc is good and no ripple?

I gradually powered up the power supply through a variac, with no load.
All voltages are nominal.

The screw on pcb is big capacitor, check the ripple.
No sign of corrosion on pcb?
Backup battery on CPU leak?

I can't see any battery leakage.  The battery is at 0.6V.  Not bad for 40 years age.
Does the battery backed RAM hold any important information?

Remove card, clean the gold contact on the edge connector with pen eraser (rubber eraser)

What I really really need is an extender card. 

juste in case...
https://fr.scribd.com/document/480870160/Wiltron-6409-service-user-ID6266-pdf

I have the original updated manual in a proper 3-ring binder.

The factory fitted fan is 115VAC.  It makes a lot of noise and supplies a lot of air for 165W load.
(EDIT)  The fan is supplied from a 115VAC winding from the transformer. 
I am going to put in a series resistor in to slow it down.


The self test indicates a "markers not found"  fault.  This could be serious.

[dazz1]

Hi
I think I have figured out why the fan is pushing so much air.
The main heat load is the power supply.  It is right next to the perforated side panel.
Keeping the power supply regulators cool requires a larger metal surface area, but increasing the size of the heat sink panel blocks air flow through the side panel.

The power supply is massively over-engineered and inefficient, so requires a high air flow over an inefficient heat sink.

If I get the 6409 fully operational, I will replace the heat sink panel with a heat sink so I can safely reduce the air flow.

[ve2ulu]

Today you have a nice 3 pin drop-in switching regulator.
All 78xx are candidates to swap for drop-in switching regulator, no need heatsink contact, no more heat.
You need ideally small film cap on input and output pin, solder directly,  to reduce high frequency ripple.
470nf to 1uf 63v film cap box are very good for that.

I do that on my Solartron 7061 and cut by half watt input on AC plug!

For fan noise, you have lot of choice, exemple: nuctuna made very efficient and silent fan, hook on 12vdc, you cut the noise with nice air flow

See youtube on vic20 and commodor 64 repairs,  some have memory trouble and is possible you have same bad chip on video card.
Some trick help to find the bad chip.


Many text on screen are in ascii in the rom, I modify the rom with my name and ajust the checksum to zero!

[dazz1]

Many text on screen are in ascii in the rom, I modify the rom with my name and ajust the checksum to zero!

OK.  that would be a neat thing to do.

Today you have a nice 3 pin drop-in switching regulator.
All 78xx are candidates to swap for drop-in switching regulator, no need heatsink contact, no more heat.

I have the metal and tools to make a decent heat sink.
I also have some suitable 12VDC computer fans to replace the existing 115VAC fan.  I also have the option of just slowing it down by adding a series resistor. 
I need to get the 6409 working before I invest time in sorting out the cooling.

[dazz1]

I have done some diagnostics on the fault that causes the vertical lines to display on the CRT. 

Behind the lines, all the front panel buttons cause expected things to be displayed on the CRT.
When the 6409 is first started, or after being reset, the CPU board is busy booting and doing self tests.  Nothing is sent to the Graphics Display Processor (GDP) to display.
The vertical lines are displayed immediately, so they don't come from the CPU.
The vertical lines are always the same pattern, which is consistent with a hardware fault.    The pattern is repeated every 16px = 16bits = 1 word.  Within the word, the pattern is confined to one byte. 
The bit pattern of the lines is:  1000 1110 0000 0000 so this looked like a problem with an octal buffer or register.  All the RAM is 4 bits wide.
All of this makes it unlikely the CPU board as faulty.


The CRT display card has an analog input that consists of a bit stream of pixels to display.  512px by 512px.
The CRT display is normal.  That eliminates the CRT display board.

In between the CPU and CRT cards is the GDP card.  This has its own processor.  The data and address bus is separate to the CPU board.  Everything points to the fault being  on the GDP card.

The GDP has 3 planes (pages) of RAM.  Each plane is a block of physically separated RAM.  The RAM is 512bits x 512bits which the same as the pixels on the CRT.

The RAM contents are loaded into a shift register (one for each plane) line by line.   The bit outputs of the 3 registers are combined in a mixer.  The mixer is a diode OR gate. 

At this point I was working on the hypothesis that there were stuck bits in the GDP. 

First problem is that I needed to identify which plane(s) had the stuck bits.   For this I used my mixed signal HP 54645D Oscilloscope.  It has basic logic analyser capability.  I probed the clock, Video planes 0,1 and 2 bit streams at the input to the mixer.  A screenshot is attached.  Plane 1 clearly shows the offending error bit pattern.  The fault is within the plane 1 circuit.

Now that I had identified plane 1 video being the source of the error, I needed to isolate the fault to a specific device(s).  To do this, I traced the path of each bit of the 16bit words, recorded in the attached spreadsheet.  Each line is allocated a bit.  Following a  line horizontally identifies each chip and pin the bit passes through.   The stuck bit pattern (almost) exactly mates data from U37 RAM.  Based on this evidence, it was concluded the outputs of U37 RAM are stuck on Hi.

Finding a replacement memory device 4416 will not be trivial.  I doubt I will find one in New Zealand.    I will likely need to locate and import one. 
The next step will be to probe U37 and confirm the diagnostics.  None of the chips, except the processor, are socketed so I can't swap chips around to confirm the fault. 

[dazz1]

Here is a photo of the Graphics Display Card with the faulty memory chip.

Also a pdf of the spreadsheet I used to trace the bit paths.

[dazz1]

A photo of the front panel of the Wiltron 6409 on top of some other classic test equipment.

[dazz1]

I have probed the U36 DRAM 4416 device to confirm beyond any doubt it is faulty. It is.
I have attached 3 images:

A close up of the graphics card.
Data write inputs (1,2,3,4) to DRAM are variable
Data read outputs (1,2,3,4) from DRAM all stuck Hi.
Probe setup.

The next challenge is finding a 4416 DRAM that doesn't require a mortgage for the house.  It's not the device, it is the shipping cost that dominates.  USA companies always want to use UPS, DHL etc, which are great within the USA, but the cost of sending a package across the USA border is mind numbing.

I don't want an ebay supplier because of the risk of fake chips.
I'd prefer a UK, Euro supplier if I can find one.

Regardless, basically this repair/restoration is stalled until I get a replacement device.  Time to rotate to the next project.

[ve2ulu]

Nice job!

I check, is highly possible i have few chip, found on old pc video card.

[dazz1]

Hi
This is the problem I face trying to buy parts from other countries.    The suppliers only seem to use courier services.  Convenient for them.  Hideously expensive for me.
Take a look at the quote for buying/shipping 4416 parts from Honk Kong.  It is even worse from the USA.

[ve2ulu]

My 6407 boot screen modified.

[ve2ulu]

I found two chip...

[dazz1]

Hi
That's great.
How much $$ do you want for the chips?
More importantly, how much for shipping?    UPS, DHL etc are excessively expensive. 
I suspect the Canada Post Small Package International service is likely to be the cheapest option.

I can pay by direct deposit into your bank account.

[ve2ulu]

Send me in personal message your adresse to check how canada post cost.

[dazz1]

Hi
I got a couple of 4416 memory chips from the UK (one and a spare).  Chips were cheap. Shipping a lot more.
Anyway having received the chips, I circled back to the 6409.

Replaced the faulty memory chip and switched on. 
This fault is fixed. 

The images show:
The CRT display with the video memory fault.  The pattern identifies the chip.  I know that now.
The boot screen correctly recognises the sensors are not connected.  Hopefully all errors should disappear when I connect everything.
The data is rubbish, but the display is good.  I have full control and, apart from missing cal data, no disturbing error messages or faults appearing.

[ve2ulu]

Nice!
I'm happy for you.
I start with 6407 in scalar network analyser wold.
Is great instrument and I have lot of fun to test and mesure filter, cavity and preamp.
Wiltron high directivity bridge are very good device.

[dazz1]

Hi
I haven't actually measured anything with the Wiltron yet.  The cal standard connectors are all corroded so I need to do something about that.
I also need to replace the battery that looks factory original, over 30 years old.

[dazz1]

OK I tried doing functional test and it didn't function, so the troubleshooting for new faults continues.

I have added individual heat sinks for all of the voltage regulators I found to improve thermal management.  Three of the regulators are running hot enough to justify investigating if there is a failing device loading them down.

Then I found a bunch of other TO220 packages that could benefit from better thermal management.
One of those TO220 devices is a voltage regulator that isn't regulating.  It has a zero Vdc output.  Most likely because of a shorted load.  Maybe a Tant cap.
Also another voltage is zeroed, so at least two faults to find.

[dazz1]

Hi
Had some success with fault finding/fixing.
So far I have fixed 3 faults.

• Tant cap failed on the YIG oscillator,
• Failed 4416 video DRAM
• Tant cap failed on the RF PCB

It now passes all self tests, but does not detect the probe, even when it is connected.    There are a number of possible faults causing this symptom.  Many wouldn't be cheap to fix. 
The hunt continues.

[dazz1]

Hi
I have made another step forward. 
I read the manual, studied the circuit diagrams and prepared myself for a good hard session of fault finding.
With the exception of a couple of pcbs, the 6409 is relatively easy to work on.  The enclosure is spacious, and removing the covers provides good access.

When I plugged in both the sensors to the inputs, the fault disappeared. 
No error messages.

Notionally, the 6409 appears to be fully operational.   Most importantly the CRT indicates a signal and not just noise.  At face, it appears the YIG resonator is working.  When I plugged in a RF signal meter to the 6409, it measured a healthy signal during the start up self test.  A good sign.  This is important because a failed YIG is the best reason to scrap a 6409.  The ones on e-bay all come untested, no warranty, most likely from scrapped 6409's. 

While the 6409 might be functional, it is not yet usable.  All the connectors plus the cal kit are corroded and need replacement.    I also need a replacement front panel, because the decal is peeling away.
I've gone far as I can with the 6409, so time to shelve it and move to the next project.  I will loop back to the 6409 when I get the connectors.

Photos show:

No error messages
some sort of signal displayed on the CRT.
ease of access to pcbs

[dazz1]

Had some more success and my first failure.

I touch tested the line of voltage regulators and 3x had an ouch response.   I checked the currents to see if downstream faults were causing the hot regulators, but the load  currents were in spec.
I decided to improve heat sinking on the 6409.  Due to the small amount of space, I custom made 3x heat sinks to improve cooling.  They are designed to work in a forced air flow. 

Improving the cooling should allow me to reduce the speed and noise of the 115VAC cooling fan.

Before I could test the heat sinks, I checked all the voltage regulators to make sure  the psu was fully operational.  That is when I had a small disaster.  I shorted pins on the LM7918 voltage regulator and destroyed it.  Now  the -29Volts  is also present on the output.  Definitely not regulating.  Fortunately I had the psu isolated so I didn't fry any downstream circuitry.

There is no local supplier in my country that has a 7918 to sell to me.   I have to use one of the international suppliers.   If I order just a 7918 I will pay $60 shipping.  As a result the 6409  goes to the end of the queue until I submit a large order for parts to get free shipping.  That could be a few months away.  I do have some replacement connectors on order, so I may come back to this project when they arrive.

In the mean time,  this thread will go radio silent.

The photo shows the 3x custom heat sinks installed. 

[ve2ulu]

I read all your development!
Use lm337 with 2 resistor in place of 7918.
Check for heatpipe, is perfect device to spread heat on large area.
Flat tube are easy to glue on aluminum heatsink and boost the heat conduction.

Switching regulator today are also very good, drop-in for 78xx and some time for 79xx regulator.
You same a lot of heat and energy.