I have repaired and calibrated vintage Smiths (AKA Jaeger) tachometers from British and Swedish vintage cars of the late '60s & early '70s for a long time. Until recently, I have been unable to repair the third generation Smiths tachometers such as those found in the early '70s V12 E-type Jaguars because they used a TI MIC7/C integrated circuit, which hasn't been available for many years. Here is the schematics for the Gen 3 Smiths tachometers:
Recently an alert customer noticed that an obsolete, but available IC called SAK215 had the same pinout and function. I thought it was worth a try to see if it would work in these tachometers. Since the only sources of the SAK215s that I can find are via eBay from China, I initially ordered 5 units to play with prior to committing to a larger inventory. After the first 5 units arrived, I breadboarded the test circuit in the data sheet, but was unable to get that circuit to function.
Fortunately, another customer had a rusty old Gen 3 tachometer from an early 70s MG that he was willing to sacrifice for the cause. So I removed the innards from the tachometer, mounted them to a base, removed the IC and replaced it with a ZIF socket on top of a modified wire-wrap socket. You can see that the test setup worked with the TI IC by the needle position in this photo:
Notice that the PCB is glued to the metal base plate. I found this PCB to be very interesting. While the schematics for the E-type Jaguar tachometers are almost identical to the MG tachometers, the E-type PCBs are traditional through-hole PCBs. But the MG PCBs are surface mount. That surprised me completely. I had never seen surface mount PCBs from such an early date.
I also noticed that there were only capacitors on the PCB, no resistors. With a little looking, I figured out that the resistors are actually fabricated into the PCBs. They are black rectangles visible on the top of the PCBs. You can also see traces on the PCB. Here are some photos from different angles that show the pads, traces and resistors of the PCB:
I found the fact that this PCB design is surface mount from the early '70s and has embedded resistors to be fascinating. FYI, the electrolytic cap was placed on top of the IC and welded (not soldered) across pins 1 & 7.
With this setup, I was able to test all 5 of the SAK215 chips and they all worked. I have ordered a bunch more as inventory for future Gen 3 tachometer repairs. I can do incoming QC with this setup to ensure that my inventory is good.
I thought some of you might find this bit of history interesting. Here's some more information about vintage Smiths tachometers if you want further reading: https://accutach.com/smiths-tachs
Does anyone have any earlier examples of surface mount PCBs or even PCBs with embedded resistors?
Stay well,
Mark
Recently an alert customer noticed that an obsolete, but available IC called SAK215 had the same pinout and function. I thought it was worth a try to see if it would work in these tachometers. Since the only sources of the SAK215s that I can find are via eBay from China, I initially ordered 5 units to play with prior to committing to a larger inventory. After the first 5 units arrived, I breadboarded the test circuit in the data sheet, but was unable to get that circuit to function.
Fortunately, another customer had a rusty old Gen 3 tachometer from an early 70s MG that he was willing to sacrifice for the cause. So I removed the innards from the tachometer, mounted them to a base, removed the IC and replaced it with a ZIF socket on top of a modified wire-wrap socket. You can see that the test setup worked with the TI IC by the needle position in this photo:
Notice that the PCB is glued to the metal base plate. I found this PCB to be very interesting. While the schematics for the E-type Jaguar tachometers are almost identical to the MG tachometers, the E-type PCBs are traditional through-hole PCBs. But the MG PCBs are surface mount. That surprised me completely. I had never seen surface mount PCBs from such an early date.
I also noticed that there were only capacitors on the PCB, no resistors. With a little looking, I figured out that the resistors are actually fabricated into the PCBs. They are black rectangles visible on the top of the PCBs. You can also see traces on the PCB. Here are some photos from different angles that show the pads, traces and resistors of the PCB:
I found the fact that this PCB design is surface mount from the early '70s and has embedded resistors to be fascinating. FYI, the electrolytic cap was placed on top of the IC and welded (not soldered) across pins 1 & 7.
With this setup, I was able to test all 5 of the SAK215 chips and they all worked. I have ordered a bunch more as inventory for future Gen 3 tachometer repairs. I can do incoming QC with this setup to ensure that my inventory is good.
I thought some of you might find this bit of history interesting. Here's some more information about vintage Smiths tachometers if you want further reading: https://accutach.com/smiths-tachs
Does anyone have any earlier examples of surface mount PCBs or even PCBs with embedded resistors?
Stay well,
Mark