NEC PC-9821Ce does not boot

[YetAnotherJPCUser]

I've got an NEC PC-9821Ce from Japan. Unfortunately the system does not boot, no beep, nothing happens. The screen stays black. When I push the reset button, the screen turns white and a continous beep sounds. Nothing else happens.

I've swapped the power supply with a psu from a friend's PC98. It does work fine in his computer.
I've replaced the onboard battery.
I made a backup of the hdd. I restored it to a cf card. The cf card does boot fine on my friend's PC98.
I tried to boot with the cf card in my own PC-9821Ce.
I tried to boot without hdd, floppy, keyboard and/or cd-rom in different combinations.
I've checked for leaking capacitors (visual check only). I don't see any leakage on the mainboard.
I removed every riser card and tried to boot with mainboard only.

Nothing helped. The PC0921Ce does always react like mentioned above.

The system has no corrosion and the case inside is very clean (almost no dust).

My monitor can display 24khz and my step down converter has enough wattage to power a PC98. I've successfully tested this with my friend's PC98. My step down converter outputs 100Volts.

I don't know what I still could do. I would be very happy about any help.

Btw, there is an empty memory slot on the mainboard. I assume this can left empty because the PC-9821Ce should have onboard memory. Am I right?

[JulBS0]

Hi,

There are two models of PC-9821Ce, the S1 and the S2, the both seems to have onboard memory (at least 1.6MB).

Look around the CPU and the overdrive socket if you see corroded or broken traces. You haven't mentioned if you had one, but if you have a CPU in the Overdrive slot, remove it.

Also, I wouldn't rule out a capacitor problem. Even if they are visually Ok, they have three decades of slow-cooking and storage behind them.

And the « computer behavior consistently changes after reset » might be a consequence of this.

I cannot find its value online nor find exactly it is connected, but C48 (right next to the CPU) might be interesting to check. Given its location, it probably filters current provided to the CPU.

[YetAnotherJPCUser]

Thanks for your feedback. A friend of mine with more knowledge about electronics replaced the capacitors around the cpu and the expansion bay area. He also discovered a broken trace next to the overdrive slot which he was able to repair.

After multiple tries the PC98 does beep once and shows a RAM test. Unfortunately the computer doesn't do anything after the RAM test.

I can enter the BIOS though.

Unfortunately the BIOS is a bit different to the common screenshots found on the internet. This BIOS doesn't have a main menu. It starts right at the dip switch settings. When I exit the BIOS the computer doesn't do anything. just a black screen. After a few tries it does boot again and my customized settings are gone. battery has been replaced.

I also have a game which can boot directly from floppy disk, but the PC9821 doesn't boot from the floppy disks. The game does boot on my friends PC98.

I've enclosed pictures from my BIOS settings. Do I have to change anything here to make it boot either from floppy or internal hdd?

[JulBS0]

Well, at least the computer is not completely dead, which is pretty good news!

When you get the RAM test, does it succeed?

You might force the system to ignore the RAM above 1MB by setting CPU to « Low » on the third screen. I'm not sure whether it will work, but it might reveal a memory problem.

And about booting on floppy or internal drive, from what I can read, your settings seems OK. You might try to set the second item on the fourth screen to the value that finished with しない, which may enable SCSI ROM.

[YetAnotherJPCUser]

Thanks for your feedback.

The PC98 does not boot every time I try it. It takes multiple times (power on/off/reset) until it shows anything on the screen. The RAM test does always succeed when it shows up.

Sometimes the system does boot in CPU low mode by itself. Unfortunately in this mode the computer does also stop after the ram test.

I changed the scsi setting, but I think it did not work because the computer does not continue after I exit the BIOS. Again, BIOS changes are not saved. Battery is brand new though.

I think the system still has an issue.

btw, is a SCSI terminator required for operation?

[YetAnotherJPCUser]

After replacing all capacitors on the mainboard the PC-9821Ce does boot into DOS now.

Unfortunately it still has an issue. The sound output is very low. I have to crank up the volume of my speakers to the maximum to hear it at all. Internal speaker and headphone jack is affected as well.

Does anyone have an idea which part I have to replace to fix this issue. I'd appreciate any hint. I'm so close to a fully working system.

[kendrick]

I apologize if you don't like this answer. Did you get the polarity of all the electrolytic capacitors correct when you replaced them? The last time I had a sound issue like what you're describing on any kind of gaming hardware, I had the caps backwards on the audio circuit. Granted, this wasn't on a PC-9821, but it seems like a common and forgivable mistake that you should check for.

[Cyothevile]

After replacing all capacitors on the mainboard the PC-9821Ce does boot into DOS now.

Unfortunately it still has an issue. The sound output is very low. I have to crank up the volume of my speakers to the maximum to hear it at all. Internal speaker and headphone jack is affected as well.

Does anyone have an idea which part I have to replace to fix this issue. I'd appreciate any hint. I'm so close to a fully working system.

You have a failed OP AMP in your audio circuit. I've seen this in 68K and FMT computers to include Marty. Exact symptoms.

If you show us some high resolution photos of the board I'll tell you what to change out.

[YetAnotherJPCUser]

Thanks to everyone for the hints. The problem is solved. There is a another board stacked over the Yamaha sound chip. After replacing all capacitors on this board, the volume via 'line out' is fine. Only the internal speaker is still too quiet, but I don't mind.