Legacy electronics product manufacturing can look deceptively simple when an older product returns to production.
The original PCB files are available.
The BOM is available.
The product has already been manufactured before.
So the initial assumption is often straightforward:
If the original product worked, why not simply reproduce it?
For industrial and laboratory electronics, however, several years can change much more than component availability.
Components may be discontinued. A replacement may match the original datasheet but behave differently in the actual system. Production test firmware may no longer be available. Optical components may require manufacturing processes that were never documented in the original BOM. Even a change to a consumable component can affect the assumptions behind existing firmware.
We recently experienced this while helping a new German customer restart production of a blood protein analysis instrument that had originally been manufactured approximately eight years earlier.
The customer already knew that the BOM was outdated. Some components had been discontinued, so from the beginning of the project, the customer asked us to identify suitable alternatives and submit them for approval before using them for prototype production.
That was expected.
What was less predictable was how many of the conditions surrounding the original product had changed during those eight years.
Before looking at the manufacturing challenges, it helps to understand why this type of instrument is sensitive to seemingly small changes.
The product is essentially an optical measurement system.
A blood sample is placed into a specific cuvette. The instrument uses a light source to illuminate the sample, and a photoelectric sensor receives the resulting optical signal. The electronics and firmware then process that signal and convert it into the final measurement result.
Point-of-care haemoglobin measurement is an established area of diagnostic technology, and measurement accuracy can be affected by factors including the analytical method, calibration, sample handling and environmental conditions. The World Health Organization provides technical guidance specifically addressing haemoglobin point-of-care analysers. (WHO)
That makes several components part of the same measurement chain.
The optical characteristics of the light source matter. The optical characteristics of the cuvette matter. The sensor’s response to temperature matters. And the calibration conditions matter.
In other words, an LED, a sensor, a cuvette and the firmware may look like completely separate items on a BOM, but their behavior is connected when they are used together as a measurement system.
That became particularly important when we started rebuilding a product whose original production conditions had been established nearly eight years earlier.
The first step was to review the original BOM and identify components that were no longer available.
For each obsolete component, we reviewed the original specifications, searched for potential alternatives, checked the available technical documentation and submitted the proposed replacement to the customer.
The customer reviewed and approved the alternatives before they were used for prototype production.
This type of component obsolescence management is a normal part of maintaining older electronic products, particularly when a product is expected to remain in production for years.
Fumax also handles BOM analysis, component sourcing and alternative sourcing as part of its broader turnkey electronics manufacturing services.
One of the discontinued components was the clock IC originally supplied by Maxim.
After Maxim was acquired by Analog Devices, the original device was discontinued.
We found a Chinese replacement that appeared to match the original requirements.
The specifications looked suitable.
The datasheet looked suitable.
The customer reviewed the information and approved the replacement.
So we used it for the prototype.
Then the prototype did something we did not expect.
It simply did not work.
At first, there was no obvious explanation.
The replacement IC met the main specifications we had reviewed. It had also been approved by the customer.
Both sides started checking the system.
The investigation continued for roughly two months.
Eventually, the problem came back to a relatively subtle difference between the original clock IC and the replacement.
The issue was not simply whether the replacement could generate the required clock signal.
The existing firmware also had to work correctly with the specific clock device being used.
The first replacement behaved differently enough at the system level that the existing firmware could not operate with it as expected.
This is one of those situations where the datasheet does not tell the whole story.
From a component-selection perspective, the replacement looked reasonable.
From a system perspective, it was not.
We therefore evaluated another clock IC from a different manufacturer.
The second replacement was tested in the actual product.
This time, the instrument worked normally.
The experience reinforced something that becomes particularly important with older products:
A replacement component can be electrically compatible on paper without being completely compatible with the existing system.
For this project, the original clock IC had been part of the product architecture for years. Replacing it meant looking beyond the component specifications and checking how the new device interacted with the existing firmware and system.
Once the clock IC problem had been resolved, another challenge appeared.
The customer was new to us, and because the product had originally been manufactured many years earlier, the customer’s current team no longer had the dedicated production test firmware used during the original manufacturing period.
The customer still had the firmware intended for the finished product.
What was missing was the separate production-test version.
That distinction mattered.
The end-user firmware was designed to operate the finished instrument.
Production testing has a different requirement: the manufacturing team needs a practical and repeatable way to verify that the unit is functioning correctly before it leaves the factory.
Without the original production test firmware, we needed another way to verify the prototype.
Initially, we used fresh anticoagulated pig blood.
This allowed us to test the instrument using a real biological sample instead of simply checking electronic signals.
But the biological sample itself quickly became a variable.
Anticoagulated pig blood is not a permanent reference.
Its condition changes over time, and its hemoglobin concentration can vary from day to day.
At the same time, we did not have specialized laboratory equipment for independently measuring the hemoglobin concentration of each sample and using that value as a stable calibration reference.
This created a practical problem.
We could put the sample into the instrument and obtain a reading.
But how could we know whether the reading was actually correct?
And if the reading changed the following day, was the instrument changing — or was the biological sample changing?
We reported this situation to the customer, who began working on the production test firmware.
Meanwhile, another solution emerged.
The customer provided a specially manufactured red plastic reference piece.
It was conceptually similar to a standardized color reference.
The piece could be inserted into the instrument’s measurement chamber.
Because the instrument’s optical system was designed to detect optical characteristics associated with blood, the red reference produced a repeatable optical response.
The production operator could then adjust the instrument’s reading to the specified reference value.
This was much more practical than repeatedly depending on a biological sample whose characteristics could change over time.
The reference piece provided something the production process needed:
a stable and repeatable physical reference.
It also made the calibration process much easier to control.
The solution was relatively simple, but it became an important part of turning the instrument from something that could be demonstrated in a laboratory into something that could be repeatedly checked during production.
The clock IC was not the only obsolete component.
The original BOM also contained a specialized LED used by the optical measurement system.
This was not simply a conventional single-color indicator LED.
The device needed to emit green light first and ultraviolet light afterward as part of the measurement process.
The original component had been discontinued.
The customer was able to provide relevant optical information from its laboratory in Germany, including the required wavelength characteristics.
We used this information to search for a suitable LED manufacturer in China.
The first supplier produced samples according to the required optical specifications.
We sent the samples to the customer.
The customer tested them.
They passed the initial test.
At this point, the replacement looked successful.
But before treating the component as production-ready, we asked the supplier one additional question:
How stable is the optical output under different temperature and pressure conditions?
The supplier did not simply answer the question.
Instead, they asked us:
“Is this LED being used for a medical or laboratory instrument?”
We confirmed that it was.
The supplier then explained something that had not been obvious from the initial sample evaluation.
The samples had been manufactured using a consumer-grade process.
The supplier could produce an LED that met the basic optical requirements and worked in the instrument.
But for a measurement instrument where optical stability and precision mattered, the supplier believed that the existing process was not sufficient.
That changed the evaluation.
The question was no longer simply:
Can this LED produce the required green and UV light?
The more important question became:
Will the optical output remain sufficiently stable when the operating conditions change?
The supplier therefore re-evaluated the manufacturing process and produced another set of samples using a more controlled process intended for applications requiring higher optical consistency.
The price difference was substantial.
The original consumer-grade process cost approximately:
US$0.06 per piece.
The upgraded process cost approximately:
US$0.27 per piece.
That is more than four times the original price.
But the price itself was not the deciding factor.
The customer needed to know whether the additional manufacturing process actually provided the stability required by the instrument.
So the new samples were sent to Germany again.
The customer tested the LED under different temperature and pressure conditions and evaluated the optical output.
The results confirmed what the supplier had warned us about.
The application required a sensor-grade manufacturing process rather than the original consumer-grade process.
This was an interesting point in the project because the first LED sample had already passed the customer’s basic test.
If we had stopped at the first functional result, the component would have appeared acceptable.
The additional question about optical stability exposed something that a basic functional test could not.
And the difference between the two processes was not merely a theoretical specification.
It changed the component cost from $0.06 to $0.27.
After the major component issues had been addressed, the project moved into pilot production.
This was when another detail appeared.
The photoelectric sensor used in the measurement system has temperature-dependent characteristics.
The available production information did not specifically state that the calibration process needed to be performed under a controlled temperature condition.
During the investigation, we reviewed the sensor’s technical documentation and found the relevant temperature characteristics.
We raised this with the customer.
The customer confirmed that the instrument indeed needed to be calibrated at 25°C.
Fortunately, the solution was straightforward.
We did not need to create a separate temperature-controlled calibration room.
Instead, we moved the calibration step to the final stage of production and performed it in the SMT production area.
The SMT workshop already operates under controlled temperature conditions, so the existing manufacturing environment could provide the required calibration condition.
The change was therefore mainly about where the calibration step was performed in the production sequence.
Once the calibration was moved into the controlled environment, the temperature condition could be maintained consistently.
The project then moved further into pilot production.
The major hardware issues had been addressed.
The replacement clock IC worked.
The new LED process had been validated.
A repeatable calibration reference was available.
The calibration process had a defined temperature condition.
But the instrument still revealed another issue during testing.
The measurement readings showed drift.
More importantly, the amount of drift was not exactly the same between different batches.
We reported the behavior to the customer so that it could be investigated from the product side.
The customer’s subsequent investigation found an important difference between the original product configuration and the current production configuration.
The original algorithm had been developed around a coated cuvette.
The cuvettes being used in the current production configuration did not have that coating.
That meant the optical conditions were different from those assumed when the original algorithm had been developed.
The hardware itself had not suddenly become unstable.
The measurement system was simply operating under a different optical condition from the one expected by the existing algorithm.
The customer subsequently updated the firmware to account for the current cuvette configuration.
After the firmware update, the measurement drift was resolved.
The product could then proceed into stable production.
Looking back at the project, the interesting part was not any single component.
The original PCB design was still usable. The original BOM was still the starting point. The product itself had already proven that it could work.
What had changed was everything around it.
Some of the original components were no longer available. The replacement clock IC required system-level validation because its behavior was not fully interchangeable with the original device. The original LED had to be reproduced with a more suitable manufacturing process. The production test method had to be rebuilt because the original test firmware was no longer available.
Then, during pilot production, the optical sensor’s temperature dependency became relevant, and the difference between the original coated cuvette and the current uncoated cuvette eventually led to another firmware adjustment.
None of these issues stopped the project permanently.
Each one simply required the original product to be evaluated against the conditions of today’s production environment.
By the end of the project, the product had gone through several rounds of component replacement, supplier validation, optical testing, calibration and pilot production.
The final configuration was not an exact copy of the product manufactured eight years earlier.
It did not need to be.
The important thing was that the current components, optical parts, test process, calibration conditions and firmware were working together as a stable production system.
The product eventually moved into stable mass production.
For an older electronic product returning to production, that can be the real objective:
not simply reproducing what was built eight years ago, but making sure the product works reliably with the manufacturing conditions available today.corporated into the production process.
And a change in a consumable component may require the firmware to be adjusted to match the new optical conditions.
For the electronics manufacturing process itself, established industry standards also provide a common framework for quality and acceptance. IPC notes that its standards cover electronics manufacturing from design and purchasing through assembly and final acceptance, helping manufacturers and suppliers communicate against consistent requirements. (electronics.org)
In this project, the product eventually reached stable production.
The original BOM was still the starting point.
The original design was still the foundation.
But after eight years, the surrounding conditions were no longer exactly the same.
Successful production recovery was therefore less about reproducing every detail of the old production process, and more about reconnecting the original product with the components, suppliers, test methods and production conditions available today.
