Forum: µC & Digital Electronics Hello Everyone and the Toshiba T2295A Chip

von David B. (Company: Puget Souind Energy) (davidba)

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I'm an electrical engineer in PSE's facility services group and don't 
have the opportunity much of asking electrical questions.  I like to fix 
things and found mikrocontroller.net with my topic of interest but it 
isn't in English.  I wish I had the English version of that topic that 
discussed the Toshiba T2295A chip.

I don't see rules for postings so kindly let me know if this appropriate 
for this forum/web site.

The T2295A chip drives the tachometer meter on a scooter that is 37 
years old.  The meter works with, say, 1.25 VDC at it passing 12.5 ma, 
so the meter's internal resistance is 100 ohms.  This is with the meter 
out of the circuit.  Meter works as a voltmeter and is fully functional, 
though labeled in RPM.

Looking back into the PCB and capacitor (driving the meter) I see 200 
kohm, but the meter always has 0 VDC in sitsu.

Is there discussion on mikrocontroller.net on how it works, expected 
voltages at the ZIP-9 chip leads, back sheets in English as 
alldatasheets.com doesn't list it?

The PCB schematic comes from mikrocontroller.net.

Later:  You know, I think I got it working.  I saw VCC and IN and they 
were swapped.  Probably all these years by the original equipment 
manufacturer.  Looking at the schematic I got from mikrocontrollers.net 
in a language I didn't understand, yet seeing those two words/symbols on 
the drawing helped me just minutes ago.  Swapped the yellow with the 
black wires to the Honda Flush tachometer.

: Moved by Admin
von Martin (Guest)

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Good afternoon sir.  Did you ever find a datasheet for this T2295A?  I 
have the same problem.  The circuit diagram you provided matches the 
circuit board that I removed from my tachometer, but I am getting no 
voltage out to the meter.  The tachometer functioned correctly for 20 
years.  Then failed.  All the components look and measure okay, so I 
want to remove the T2295a and pin check it.  But I can't fond the 
datasheet anywhere.

von David & Lois Babbitt (Guest)

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No, never got a pinout of the chip.  Wiring was actually correct and for 
some reason the tachometer works in the scooter.  Someone told me to 
replace the largest capacitor but I didn't do that.  Did you?

von Martin (Guest)

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Hi, thanks for the fast reply.

I have not replaced any components yet.  On the test bench I can measure 
the pulses entering the chip @ pin 2, but no voltage out on pin 6.  But 
I am very new to circuits and diagrams, so I may be off base.  The short 
of it - I detached the the board from the rest (coil / needle) and when 
I power the needle portion only, it works.  When connected to the board, 
does not work.  I am putting 1 kHz 12 volt pulses in.  Those drop across 
the R1 resistor, so they are about 2 volts at the pin into the IC.  I 
assume that's correct - the resistor is good, and there is nothing else 
between.  After that...nothing out.

I can order a chip off eBay for about 5 bucks.  I might just swap it out 
and see if that works.  I might try changing that cap too.  Parts are 

Stay healthy!

Thanks for the tip, and BTW, the diagram you posted was really helpful!

von David & Lois Babbitt (Guest)

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You're welcome.  I thought it fortunate that I could even find the 
schematic, somewhere.

von Martin (Guest)

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Hi, I changed that cap (6.3v / 1000uF).  The tach is working again, so I 
guess that was the problem.  Cheap fix.  Cap cost $1 at the local 
electronics supply store.

Thank again!

von David & Lois Babbitt (Guest)

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Hey, that is great!.  I would have to thank whomever told me about the 
capacitor replacement. David Babbitt

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