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NEC TG-16/TE/TurboDuo => TG/PCE Repair/Mod Discussion => Topic started by: Pinkstone on July 11, 2025, 06:58:25 PM

Title: Turboexpress Control Problem (Only two buttons don't work.)
Post by: Pinkstone on July 11, 2025, 06:58:25 PM

Hi, first time poster here. I replaced all the caps and the Q900/1 in my Turboexpress. Both video and sound work perfectly. However, the Run and Left Pad buttons don?t work, while the others work fine. I replaced the controller board, but no change. Turbo buttons have continuity and are clean. In the mainboard, I don't see any broken tracks anywhere. Any ideas?

Thanks!!!!

(https://i.imgur.com/ZQtWMfc.jpeg)

(https://i.imgur.com/dQ3z0U9.jpeg)

(https://i.imgur.com/sf753L2.jpeg)

Title: Re: Turboexpress Control Problem (Only two buttons don't work.)
Post by: Keith Courage on July 12, 2025, 05:22:16 AM

That stinks.

Usually if I work on a system that has controller button issues but the problems are not related to faults with the controller board, it ends up being a faulty HU6280 CPU

You can test controller button functions directly from the CPU. Simply use a wire. One side of the wire soldered to ground somewhere(doesn't have to be ground on the CPU itself) then touch the other end to the pins for button functions to see if they work or not. Simply test each pin with the colored lines shown on the picture below to see if each one performs a button press when connected to ground. If one of the pins does nothing, well then it's a faulty HU6280 chip.

(https://i.postimg.cc/6T5QgG4F/Pc-Engine-GT-Turbo-Express-Controller-Mod.jpg) (https://postimg.cc/6T5QgG4F)

Title: Re: Turboexpress Control Problem (Only two buttons don't work.)
Post by: Pinkstone on July 12, 2025, 09:48:25 AM

Thank you. I will do that in the next days.

Title: Re: Turboexpress Control Problem (Only two buttons don't work.)
Post by: Pinkstone on July 13, 2025, 12:02:28 AM

Hi, the huc6280 works fine so I followed the traces down the connector. The problem is the upper resistor of the r718 pack (820 ohm) that was cracked in the middle and lost continuity. So I'm going to replace it. Is that ok if I bridge it?

Thanks!!!

Title: Re: Turboexpress Control Problem (Only two buttons don't work.)
Post by: Keith Courage on July 14, 2025, 01:32:17 AM

I think those are 330 Ohm resistors. Check using a multi meter and just solder in another resistor of the correct value. It may not cause any long term damage just bypassing it, but I'm sure the resistors are there for a reason. You don't have to get a super small 0603 surface mount resistor. Any size will do as long as it fits and it's the correct value.

Glad you found the issue.

Title: Re: Turboexpress Control Problem (Only two buttons don't work.)
Post by: Pinkstone on July 14, 2025, 11:50:29 AM

All is working well now. The R718 is (very) tiny 820 ohm resistor as you can see from the smd marks (821).  So, another (turboexpress) that doesn't bite the dust  :D

Thanks!!

(https://i.imgur.com/RXtufQL.jpeg)

Title: Re: Turboexpress Control Problem (Only two buttons don't work.)
Post by: Necromancer on July 14, 2025, 12:55:32 PM

Huzzah!  Congrats on fixing another system!

Out of curiosity, what're the blobs of gray stuff that look like clay?

Title: Re: Turboexpress Control Problem (Only two buttons don't work.)
Post by: Pinkstone on July 14, 2025, 01:08:45 PM

Thanks!!! I'm very happy right now. Regarding the gray stuff,I think is an epoxi glue. It came with the PCB.

Title: Re: Turboexpress Control Problem (Only two buttons don't work.)
Post by: Keith Courage on July 15, 2025, 01:36:00 AM

Quote from: Necromancer on July 14, 2025, 12:55:32 PM

Huzzah!  Congrats on fixing another system!

Out of curiosity, what're the blobs of gray stuff that look like clay?

That gray stuff is inside all Express and GT systems in that one spot. That's where the Power jack and other related parts are located. Probabaly to insulate those parts from accidentally grounding out against the rear of the stock screen.