Almost fixed my Simasimac SE/30 (booted once!)

[mrpippy]

Spent today trying to get my SE/30 working, and I did get it to boot once!!

It's always had the classic horizontal stripes SimasiMac, without any chimes. I replaced all the caps, without any luck.

I was poking at signals today and found that the reset switch is bad--it was around 500 ohms between the terminals without the button being pushed, which must have been causing problems. I removed R5 to disable the reset button, after that it booted to the flashing question mark! I even got a startup chime when I plugged in a speaker.

I then turned it off and wired in Q3 (a 2N3904 for ADB, it had corroded off). After that it won't boot again, it's having the same symptoms:

RESET* is acting odd. Sometimes after powering on it's around 0.7V, and sometimes will goes up to 5V after a few minutes. No change after it goes high though.

Once RESET* goes to 5V, VSYNC goes to 60 Hz.

Also the 5 PALs (UE6, UE7, UG6, UG7, UI6) are all pretty warm after a minute or two. I can keep my finger on them, but they're much warmer than the 68K or other chips.

ROM CS is high, doesn't change. ROM address lines also don't change. OVERLAY is also high.

CPU is socketed but I haven't tried pulling it out. The 16 MHz clock is running also.

Anyone have any ideas for what to try next? I tried pulling the sound chip high (2K between Sony sound UB11 pin 7-15) but no change.

 

[techknight]

Reset is controlled by the sound chip if there's an issue with that chip you'll have this

 

[Elfen]

After the "fix" is done, you can spray the reset button with contact cleaner as you press and depress the button, spraying along the button and its frame to clean it out and maybe that will solve the switch problem. Then you can restore R5 back into place.

TechKnight, which Sound Chip? There are two Sony Sound Chips by the Reset Switch as I see on my SE/30 board: UB10 and UB11. Unless you mean UE10 further down the board which is made by Hitachi.

 

[techknight]

No. I am only referring to one of the sound chips. Its in the schematic

 

[mrpippy]

Yep, UB11 connects to the reset line. Both UB10 and UB11 on my board have some corrosion on the legs, I'll pull them out and re-solder (or put in a socket if I can find one)

 

[Elfen]

I need to get that schematic. Is there a link for me to download it?

 

[mrpippy]

This zip file has the Apple and BOMARC schematics in it. Apple schematic is more accurate/easier to read, but BOMARC is sometimes useful to look at.

 

[Elfen]

Thanks a lot Mr Pippy!

 

[mrpippy]

I pulled out UB11, cleaned it and the board off, put it in a socket and back on the board. Still wouldn't boot 

But after a few more power cycles, I got it to boot again! Then went to wire Q3 on, and stripes again 

And most of the time I get stripes, RESET* is at 5V. As long as RESET* is high, does that mean the sound chip isn't causing the problem?

 

[techknight]

Did you make sure your Q3 replacement is correct? 

 

[mrpippy]

It's just a 2N3904 wired to (what I'm pretty sure are) the right places. It's never booted with that installed, but it's failed to boot many times without it as well.

I did the same thing last night after it booted--hooked up Q3, saw it didn't boot, disconnected Q3, and it still wouldn't boot.

So it's not proven good, but also not proven bad

 

[techknight]

Well you need to check the impedance in the reset circuit. Make sure it isnt too low, or shorted one way or another. I think the Sony IC is to blame. 

 

[mrpippy]

Hmm how would I check that? I can use a scope and try to see how long it takes to rise vs. +5V.

Would the machine boot without UB11 installed at all? I see RP7 pulls it up to 5V, is UB11 actually driving it high as well?

I don't have any other sound chips to swap in there, but I could wire UB10's RESET line to the system reset line (as well as the TEST* it's already hooked up to)

 

[Elfen]

Found this while looking for a replacement for the Sony chip, its from a Japanese Mac SE/30 Site, already translated into English.

http://www.biwa.ne.jp/~shamada/fullmac/repairEng.html#SimasiMac

Scroll down a bit to Solutions, and then 5, ad then 6 just below it.

 

[Elfen]

Some times I hate custom parts... After googling about, many sites want you to sign up to their service and then you have to request a price quote for the chip.

The only site I found that did gave  price is in China, and they only sell it in Lots of 10 for about $60, or $6 a chip. In my mind, cheap for a single custom made chip, but I don't need 10. Also its coming from China, so delivery to the USA is between 3 to 6 weeks minimum. I do not know about the rest of the globe. Maybe you can talk to them about selling you just a pair? Here is it's URL:

http://www.aliexpress.com/w/wholesale-3430045b.html

The other sites that want you to sign up and request a pice quote are here:

http://www.hobid.com/electronic-component/3430045B/

http://octopart.com/3430045b-sony-15668215

 

[techknight]

If the sound ic works otherwise, all you need from that point is to disconnect the reset line from it to the system.

Then use any off the shelf reset management/BOD ic and sub that in.

 

[mrpippy]

I tried disconnecting RESET from UB11 and wired UB10s RESET line to the hole instead, still shows at 5V but no change. I'm starting to think maybe there's a problem with the trace carrying reset to the sound chip, I'll try a separate wire for it

 

[mrpippy]

Tried the extra wire for RESET, still no change. RESET is at 4.82V when the system is on. I also disconnected Q3 again, still no change. The SENSE pin to the sound chips is also +5V like it should be.

Thanks for your help techknight, do you have any suggestions to try next?

 

[Elfen]

I've looked at the schematics (Sound and Serial - File P7 of those you gave me). The only thing that caught my eye as C16 ( .1µf) on the bottom of the board. Its parallel to the Reset Button (both to ground). So if C16 is shorted out then it would hold the reset down. It would also look like the reset button is shorted out.

Have you tried removing C16? And then test the reset button.