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Hello Dave,

You are not missing the schematic supplement, it is not published or
sold anymore.

I am not sure if this is because of IP inside or because they don't want
you to repair the product to force you to buy a new one. Or maybe both?!

Another topic related to the new designs is that they use a lot of
micro-controllers and FPGAs and even if you would have the schematic and
let's say you can get the exact part number to replace the
micro-controller or the FPGA you will not get the microcode/software to
write it back. So it is pretty useless for the new designs to get a
schematic if you cannot get the complete firmware for individual components.

Regards,
Razvan

Consider that we live in an amoral litigious society, where
companies have patented just about every conceivable
combination of thoughts, algorithms, or circuits, that have
happened in the past, present, or future, and covetous lawyers
roam the planet sniffing out shares of any monies that can
be taken from the legally weak.

In such a society, it is impossible to design circuitry when
you have to challenge your every thought, and trace the origin
of your every idea just to see who owes what and to whom...

So why, in such a society, would you put your company in the
sights of marauding lawyers by freely revealing exactly what
you have done inside of your circuits, ASICS, ROMS, and FPGA's?

Make the b**tard lawyers work for their plunder!

Component level servicing manuals are a relic from a much
friendlier time; a time when most people had moral values,
and lawyers were few, and traded their craft for livestock and
produce.

-Chuck Harris


On Mon, 26 Aug 2024 04:59:29 -0700 "Dave B" <davebullockmbe@...>
wrote:

HI, well I suspected that may be the case and in the digital side of
the instruments, (as you say) one wouldn't have a chance of a repair.
However I would have imagined that just about every possibility of RF
circuitry would have been explored by now so wouldn't particularly be
top secret? And, even in my HP 1725A 'scope they used 'hybrid'
(secret?) modules, and just depicted them as a block but showed the
rest of the analogue workings as a 'proper' schematic. It's
frustrating as I'm developing a tiny solid state (plug and play) LED
backlight 'module' to replace the CCFL inverter and tube. The
backlight is borne to fail as the CCFL lamp dies after a while. The
inverter and lamp were (I believe) made easy to replace as they are
pretty accessible without having to access any of the electronics
within the sig-gen. (It's just behind the front panel). However,
without knowing what is supplying the +5v and the dimming control
voltage could easily be answered if a schematic was available.
Questions like:- Does the control come from a DAC (I think it does)
but what drive capability does this have. Is the output of the DAC
protected by a series resistor? Whilst I could start to take the
instrument internal covers off to trace this out...........sigh! Dave

I've considered such replacements as I do design microprocessor boards with (replaced by LED) CCFL displays.

Many of the inverters have a DC control voltage as you know.? I'd be tempted to have the LED string capable of working off the dc supply voltage for the inverter, and I'd bag the whole idea of worrying about the DAC.? Feed a very small (8 pin or so) microprocessor's A/D input through a divider and let the processor generate the PWM.? That, with a transistor level shifter allows you to use a P channel power FET to control the LEDS.

IF you had access to the software and IF it had an I2C interface you could control on the main board, something like a PCA9634 FM LED controller would be overkill, but would work.? I use that LED controller on my generic boards and just reserve one channel of 8 for the display backlight.

Harvey

inline.

On 8/26/2024 11:48 AM, Dave B wrote:

HI Harvey,
Your creations sound far superior to my KISS approach to the issue.

Sometimes I think more may be less...

I have been designing my replacement 'module' with the idea it just 'drops in' in place of the existing inverter.

this would fit in the same space as the inverter board.? An 8 or 14 pin microprocessor (depending on innards), a very tiny regulator, a few SMT resistors and two transistors (one a DPACK).

I have watched an interesting Youtube video of a complicated attempt to solve this problem and gleaned the control voltages and supply data from this.
I have not ventured inside the instrument I have on my bench yet, as I only want to go inside it once!
It looks like there is a 3 pin connector with +5V, GND and a variable 'Dim' control voltage.

Then the 5 volt can be a bit of a problem.

Think 20 ma/LED, and 9 LEDS fit in a strip (I have such strips, pc board wise).? So maximum non-PWM controlled current is about 180 ma/strip, and that, for 2 strips, is 360 ma.? The problem is that the LEDS may not have enough voltage for 2 in series.? Hence parallel.

What's done in some LED backlit displays is to put the LEDS in series (say needing about 18 to 20 volts), and then run them with a small inverter.? That inverter might just have brightness control....

They make chips for that.? So perhaps that chip, a few transistors, a small inductor might just do the job for you.

According to the video, the control voltage varies from 0.7V (display off) to 4.7V (full brightness) set by rotating the front panel adjustment.
So...
I'm assuming that the HV inverter would be taking a much greater current from the 5V supply than a few LED's to generate the same light as a CCFL, so that's the supply sorted?

Depends on number of LEDS, and hookup.? So not quite so easily sorted.

My concern was that without a schematic I don't know what the source impedance of the control voltage was, leading to my 'missing schematics' discovery!
As you hinted, I am powering the LEDs off the 5V and using a high impedance analogue input device to exacerbate any loading issues.

That works.

Assuming the voltages are the same on this instrument as measured on the video, then I should have a CCFL replacement backlight module for a great deal less
than an OEM module.

Which is a good idea.? Multiple ways of getting there.

It all works on the breadboard, I'm just waiting for the pcb's to arrive to start manufacturing and carry out a real life test.

Ah, then you've gone further in this design than I thought.

Best of luck, then, and let me know if I can contribute more ideas.

Harvey

Dave

Today’s corporate focus on product manufacture and service is many fold.

Profits made from equipment sales are only part of the equation. There is (sometimes much more) money to be made through support. If you don’t provide good documentation the customer is basically faced with having to send the item in for repair.

Second, in order to produce a very detailed document describing every nut and bolt on how to fix the item requires a gaggle of tech documentation people which costs $$$ to employ. Make manuals simple and you have fewer related employees to deal with.

Third, it has been shown that if users do choose to repair their own equipment that fixing things at the higher level (i.e. PC board, etc.) proves to be easier both for the customer and the factory service department where it reduces time to fix. Neither the customer nor the factory needs to dig deep to find a problem if they follow the simple diagnostic charts provided in the manuals. And factory service effort is reduced by simply plugging boards into test fixtures to localize the fault. Or, if more economical, they may opt to simply scrap the boards and present a new board fee for the user when they purchase through “exchange.”

There is more but I will not continue. One must remember that we now live in a “disposable society” where people need instant everything which includes immediate replacement if something breaks. As for those of us legacy equipment collectors/users down here in the trenches we gradually see our inventory becoming older and older in age as we either cannot or opt not to try to fix “mystery boxes” now being manufactured. And as it has been said by others in previous posts, opening a box only to see a PC board with only one non-repairable module in the center of it certainly adds to the issue.

And even if that module can be replaced by ordering another from the manufacture time is of a limit given the shorter and shorter time replacement part inventories are held after the manufacture is discontinued for that device. It’s expensive to store parts for old equipment since everyone wants the “latest and greatest” products and will achieve that goal by perpetually buying more new ones. From that the importance of supplying parts for legacy equipment becomes less and less. It’s the corporate “bottom line” speaking here.

A note on sending equipment out for repair. Yes, there are those third party agencies that will offer service long after the factory does not. But what I have seen even through actual visits to these places is that they, too often have scanty data to use to fix stuff. From that many of them will tell the customer that the item cannot be repaired and if the customer opts to simply abandon the item with the repair agency that agency will relinquish it to a “bone yard” where they can use parts out of it to fix other units.

Greg

Hello Frank,

From your point of view maybe it is short-sighted but I encountered
issues in the past where we had some Altera and Atmel ICs that was
faulty including other passive components around them and we replaced
all of them with new parts but the system wouldn't work. Contacting
manufacturer didn't help. They don't share the files to rebuild the
equipment and since we repaired it they don't want to accept it for
repair also.

In theory you can repair everything but in reality you cannot do it.
Most test equipment now is running some custom PC board that in theory
can be repaired but if some NAND flash is damaged and you cannot get the
full firmware how you will fix it? Most vendors will say it is
"proprietary" code or what ever and they will not provide it to you.

What I would like to have is the PSU schematics at least. I saw a lot of
new test equipment with PSUs broken/fried and many of those PSUs were
very complex full with SMD components.

Maybe you can share more details related to fixing modern test equipment
to understand the complexity.

Regards,
Razvan

Does the customer deserve information on how to
repair an incandescent light bulb?

Perhaps the customer should be given access to cheap
replacement tungsten filaments?

Or, if that isn't practical, instructions on how they
mixed and forged tungsten?

Should the manufacturer be required to include a
service port on each light bulb to make the filament
reachable without damage?

-Chuck Harris


On Mon, 26 Aug 2024 13:00:01 -0700 "Frank Mashockie"
<fmashockie@...> wrote:

Razvan,

Your points are valid, but my point is don't give the manufacturers
the benefit of the doubt.? The customer deserves this information.? I
apologize as I came off a bit strong with my wording.

Unless the MCU has failed completely, I've ran into many cases where
only a GPIO pin or two has gone bad.? In these cases, flashing the
MCU is still an option.? As long as it isn't read protected (you'd be
surprised how many manufacturers don't, especially on older
equipment).? Or by sharing firmware of MCUs you've flashed with
communities like this (or EEVBlog), all you need is a new MCU to
perform the programming.? Sure it may take some additional tools, but
it is pretty easy in most cases.

As consumers, repairs, or designers we shouldn't allow manufacturers
to continue these repair prevention strategies that ultimately stifle
the sharing of information and community knowledge.? We shouldn't
give them the benefit of the doubt that it is acceptable to forgo
sharing of schematics just because the equipment has an MCU or FPGA.
That doesn't stop manufacturers from protecting their creations
either.? For example, in pharma, a drug can be patented, yet we still
know the chemical composition.? It is not kept secret; the entire
public knows.? It should be no different for electronics.

-Frank

As usual, something between the ridiculous extremes would be the best situation.? Between say, manufacturers being forced by the government to divulge all their secrets and consumers forced to have every single product returned to the mfr for repair.? ? ? ? ? Jim Ford, Laguna Hills, California, USA?

That assumes you have the time to reverse engineer the faulty product, at least to some degree.? These days I'm commuting about two and a half hours each day, so not having at least a schematic usually prevents me from being able to repair much of anything.? ? ? ? ?Jim