[eprom]

I have attached the D14 Pin Power Schematic to this post.
It is in this circuit that the only thermistor of the MCM is used.
So at this point, I see no circuit to measure the temperature in the MCM.
The only option I haven't explored would be to have it done internally by the microprocessor.


Does anyone have any idea what NF8 is? I guess it's Noise Filter, but how to note this component on the diagram?

 

[mudder]

Thanks for looking into whether the MCM has an ambient temp sensor.
Die temp wouldn't be useful for measuring ambient temp.
NF8 is probably a pi filter, with a series inductor and a parallel capacitor (to ground) on both sides.

At this point I suspect it's the ECM that's commanding regen when it's cold outside. This is easy to test if you're experiencing the 'background regen when cold' issue and have a manual IMA controller.

 

[eprom]

I just made a new update
I added the supply circuit schematic, there was VCC I added Filtered VCC.
It is used in certain analog measurement circuits on page 2

For now there is only D30 left at the 12V input which I am not sure what it is.
I couldn't find anything about this component on the internet.
In my opinion this component would benefit from being a zenner, because it would protect against an overvoltage that would blow up a fuse in addition to protecting against a reversal of polarity on the 12V.
But I did not do any test on this component to identify it.

 

[eprom]

here is an overview of the next part which will soon be added to the schematic.
I do not know exactly the function of this circuit because I find absolutely nothing on the component IC22 TA8903sn.
I know that this component was used in old civic, integra and also in toyota.
That it is a fragile component that is sometimes replaced in cars other than insight.
IC22 can generate a non-maskable interrupt to the cpu, it can also reset the microcontroller.

I don't quite understand the purpose of transistor Q16 which is bypassed by D31.

One point that I noticed the capacitor C32 is electrolytic, it is always powered, so to date on the insight 2000, this capacitor has been powered continuously for 23 years, it is possible that it is starting to age.
I found mine a little rounded but I couldn't unsolder it to measure it because there is a large thermal mass underneath.

--updated the schematic 22 march 2023

 

[*sean*]

Perhaps the TA8903SN is has a supervisory function perhaps holding the CPU in reset until the power supplies have come online?

On what side of D31 are the filter capacitors? Perhaps the TA8903SN it senses the loss of power and issues the NMI and the diode keeps the filter caps from discharging back into the rest of the (shut off) supply circuit???

This might be one of those things that a Saleae Pro 16 (which has 16 channels that can be digital or analog up to 10 or so volts) would answer. They are expensive, but you can get a very significant enthusiasts discount if you don't use them for work for a year. I use mine for my High Resolution ECU Signal Monitor in my thread Sorting out a Citrus. Sixteen analog or digital channels make fast work of problems like this. Saleae Discounts

EDIT: apparently it is a Power Supervisor IC. But the links in the post that refers to it as such are dead. Wish I had kept all those old databooks. Odd electrical issue fuel pump doen't prime - Honda-Tech - Honda Forum Discussion

 

[eprom]

Thanks @*sean* for your find

apparently it is a Power Supervisor IC.

pgmfi.org • View topic - What components are involved in fuel pump activation delay?

In this link someone tried to determine what this component is, it was not complete, but with my diagram, his and the PDF of the MAX807.
I have already identified some parts of the TA8903SN and I continue.

On what side of D31 are the filter capacitors? Perhaps the TA8903SN it senses the loss of power and issues the NMI and the diode keeps the filter caps from discharging back into the rest of the (shut off) supply circuit???

the capacitors of VCC are on the left so your assumption for D31 is incorrect, but thank you for trying an explanation

 

[mudder]

I don't quite understand the purpose of transistor Q16 which is bypassed by D31.

Q16 is an LDO regulator. When IC22 drives pin 10, the voltage drop across Q16||D31 will be much less than it would be (~0.7V) when Q16 is off.

One point that I noticed the capacitor C32 is electrolytic, it is always powered, so to date on the insight 2000, this capacitor has been powered continuously for 23 years, it is possible that it is starting to age.
I found mine a little rounded but I couldn't unsolder it to measure it because there is a large thermal mass underneath.

You'll need a board preheater and/or a heat gun to remove it. Note that capacitor aging is a function of the actual applied voltage, versus the maximum specified value. For electrolytics, typically you'd want Vrms to be less than 65% of nominal rating.

 

[eprom]

This is the voltage on all pin of TA8903SN at the first time only 12V is applied on VBU
then I add 12V on the input of the regulator that generate VCC
then I removed the 12V on the input of the regulator that generate VCC to let only 12V like it was at my first mesurement

	first power with only 12V at B10 (VBU)	with only 12V at B10 (VBU) and VCC = 5V	power with only 12V at B10 (VBU) after vcc shut down
IC22 TA8903SN pin 1	0V	4.95V	3.4V
C22 TA8903SN pin 2	0V	5V	0V
C22 TA8903SN pin 3	0V	4.57V	3.2V
C22 TA8903SN pin 4	0V	4.96V	3.46V
C22 TA8903SN pin 5	gnd	gnd	gnd
C22 TA8903SN pin 6	gnd	gnd	gnd
C22 TA8903SN pin 7	0V	4.78V	0V
C22 TA8903SN pin 8	0V	4.21V	0V
C22 TA8903SN pin 9	12V	11.99V	11.47V
C22 TA8903SN pin 10	0V	0.41V	3.03V
C22 TA8903SN pin 11	0V	2.513V	0V
C22 TA8903SN pin 12	0V	0.022V	3.46V
IC3 - 11	0V	0V	3.46V
IC3 - 6	0V	5V	3.4V
IC3 - 3	0V	0V	0V

With these measurements, I believe I have identified the pin-out of TA8903SN

pin 1 is an output, there is 4.95V when VCC is present on pin 2 otherwise there is 3.3V generated from pin 9
pin 2 is VCC input
pin 3 is normaly high, I'm not sure when it goes down to 0, maybe for a short moment when VCC is applied but I'm not sure.
pin 4 dont know what is it
pin 5 gnd
pin 6 gnd
pin 7 maybe an RC timer to do a reset when VCC goes up
pin 8 generate a power fail warning 4.2V when pin 2 is high and 0V when pin 2 is low
pin 9 Backup Power
pin 10 transistor driver
pin 11 input VCC/2 - I dont know if it is true only when VCC is 5V but when input VCC is 0V pin 11 is at 0V
pin 12 low when 2 volgate source are there high when ignition is off and only one supply source present.

by these measurements, I can say that the CPU of the MCM is always powered
and IC22 and the components it powers consumes the following current: (12V - 11.47V) / 2200ohm = 0.24 mA when ignition is off

 

[mudder]

Maybe you can glean information from these pages:

TA8903SN IC17 Toyota Replacment/Emulator Honda OBD1 Apollo Tuning | eBay

Find many great new & used options and get the best deals for TA8903SN IC17 Toyota Replacment/Emulator Honda OBD1 Apollo Tuning at the best online prices at eBay! Free shipping for many products!

www.ebay.com

IC17 Replacement

TA8903SN emulator. This fixes the problem with many dead obd1 honda ecu's that will not activate the main relay/fuel pump or its delayed. Available in bulk just select quantity from the drop down menu. Reference to install direction in second picture.

jasonwaterstuning.com

TA8903SN TOSHIBA | TA8903SN Electronic Chips Distributor | TA8903SN MG100J6ES52 TC551001CFTI-70L 2SC4685 TC4069UBFN stock available from veswin.com

TA8903SN, MG100J6ES52 TC551001CFTI-70L 2SC4685 TC4069UBFN from TOSHIBA Electronic Chips at Veswin Component Distributor, TA8903SN large in-stock quantities. PayPal accepted, inquire TA8903SN Specifications online at veswin.com or RFQ Email [email protected]

www.veswin.com

Looks like it might be a quad transistor IC.

 

[eprom]

Did you manage to download the datasheet ?
The link doesn't seem to work for me.

The image we see of the replacement on ebay seems to contain 1 transistor an IC two capacitors and 5 resistors,
However we only see one side on the other picture from jasonwaterstuning.com it the circuit looks much smaller.
I have read on forums that some of these replacement parts do not work.
I don't know which work.

with the tests I did it is certain that the original contains a 3.3V regulator
If I look coldly it would probably be possible to make a replacement with a diode from pin 2 to pin 1 and a 4V regulator which would be powered by pin 9 then a diode at the output of this regulator to pin 1 which would would provide supply.
we could place a diode from pin 1 to pin 3
we could connect pin 2 to pin 8
With two resistors of the same value to make it a voltage divider it would be possible to divide pin 2 to make the vcc/2 of pin 11 that the MCM does not use but other cars use.
A resistor between pin 1 and 12 and with a transistor that shorts pin 12 to gnd when pin 2 is powered to manufacture a part which to repair ECUs which require the TA8903SN does not seem very complicated to me, on the other hand if we would like to be certain to keep all the functionalities, it would be better to study the function of pin 7

It is quite possible that some of the replacement parts cannot generate a reset or an interrupt I wouldn't buy to test them but if these parts don't generate all the signals, it would be fun to create a really better one, especially since it probably wouldn't take a lot of time :+)