alexthekid wrote on 2024-07-25, 22:58:

Hello everyone,
I am currently repairing an old Toshiba T1000SE Laptop ~1990. It works now (yay!) but there is a component that I think doesnt work as it is supposed to. It is labeled "M01 1025" and it is in a SO8 package. The "M" looks similar to the Microchip Technology Logo but is a little different. It is located near the PSU circuit(s) on the Motherboard and all the RAM-IC +5V-terminals (also the RAM expansion slot +5V) are connected to Pin 6 of this IC. Under heavy RAM-access the RAM-Supply-Voltage drops under ~4V and the Laptop powers off. This becomes worse when a RAM expansion card is installed. Then a simple DIR on the RAM-Drive leads to a system shutdown. These shutdowns do not occur when I use an external +5V for the RAM. I therefore assume that this IC is a (Low-Drop) Voltage regulator but I am not 100% sure. If somebody could provide a datesheet that would be awesome. Here is a picture of the IC.

The attachment IMG-20240403-WA0000.jpg is no longer available

It should be a Mitsumi MM1025 - looking that up on Google shows a very similar IC but with a Z on the end and you can find datasheets for it too. It's apparently a reset IC? See a datasheet here: https://semiconductors.es/datasheet-pdf/527533/MM1025.html

While I don't know a thing about the Toshiba T1000SE, I know that chip logo and that you can find Mitsumi ICs in Toshiba and other computers from the 80s/90s.

Thank you. I will check if it fits the descripion in the datasheet.

Also, it seems that Mitsumi was using this logo in the 90s.

I found the MM1025 on ebay. Looks exactly like my chip. Reset chip would also make sense in this position. Pin 6 (connected to +Vcc of all the RAM-ICs) is Vout according to the MM1025 datasheet. That also makes sense. Since my RAM- Voltage is unstable I will replace the MM1025 and see if this is enough to fix it. Thank you Thermalwrong! 😀

alexthekid wrote on 2024-07-26, 07:01:

I found the MM1025 on ebay. Looks exactly like my chip. Reset chip would also make sense in this position. Pin 6 (connected to +Vcc of all the RAM-ICs) is Vout according to the MM1025 datasheet. That also makes sense. Since my RAM- Voltage is unstable I will replace the MM1025 and see if this is enough to fix it. Thank you Thermalwrong! 😀

Hi, I'm just curious to how your repair went, did the MM1025 work?
Brgs,
Tom

tomdegerth wrote on 2024-10-05, 11:43:

Hi, I'm just curious to how your repair went, did the MM1025 work? Brgs, Tom […]
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alexthekid wrote on 2024-07-26, 07:01:

I found the MM1025 on ebay. Looks exactly like my chip. Reset chip would also make sense in this position. Pin 6 (connected to +Vcc of all the RAM-ICs) is Vout according to the MM1025 datasheet. That also makes sense. Since my RAM- Voltage is unstable I will replace the MM1025 and see if this is enough to fix it. Thank you Thermalwrong! 😀

Hi, I'm just curious to how your repair went, did the MM1025 work?
Brgs,
Tom

Yes, it did. Sorry for my late reply.

Btw: It is a Mitsumi-Chip (Thank you Thermalwrong !). It's a System Reset IC(with battery back-up). The Datesheet is still available online. I bought a bag containing some MM1025A, MM1025C and MM1025Z, but no MM1025 without suffix. Unfortunately there is no info in the data sheet about the Suffix, so I built a small test circuit and the 1025Z behaved as the 1025 is supposed to behave. (I did not test A and C). Anyway, my T1000SE works fine now with a MM1025Z.