Heavily modified Mega ST1 does not boot

[+slx]

For curiosity's sake I acquired a heavily modified Mega ST1 which - more or less expectedly - does not boot.

 

It has a strange stack of sockets with a small board on top of the CPU and a "flying" RAM board installation. The fan turns and the floppy seeks when I turn it on but there is no picture. (I have no way to test my monitor but it worked about 2 years ago)

 

I have a logic probe and a multimeter for testing but no scope. As some pins of the TOS ROMs were corroded, I re-seated them but that didn't change anything. 

 

The battery line is disconnected as the battery compartment is more or less corroded away.

 

Any hints (or offers ) welcome.

 

[+tf_hh]

One of these typically homemade installations of the 90s... ?

 

Are there ROMs/EPROMs installed? The RAM PCB covers the lower sockets. I suggest there was a TOS 2.06 adapter PCB with CPU sitting in the CPU´s socket. So if no ROM/EPROMs inserted, you need such a TOS-card or re-install standard ROMs for TOS 1.0x.

 

The upper CPU socket is heavily oxydized, remove and exchange it complete. The little PCB between is the blitter correction part, it must be present.

 

The GLUE and MMU are made by IMP... these ones are best known as trouble maker. The chances are high that you never get a real stable system with these.

 

if there´s no ROMs and no TOS-card, check for more modifications. Maybe somebody has removed expansions like OverScan ST, which require cutting of traces.

 

[snarkdluG]

Clean or change sockets if necessary. Reseat MMU and Glue. Clean with IPA both socket and chip. 

 

Get a test cartridge and see if you get anything on screen. Otherwise hook up a null-modem cable to other computer when booting with test cartridge. 9600 baud.

 

Probably some RAM chip or something to do with RAM that has broken. But I'm just guessing here.

 

By the way, is there anything on the screen now? All white/all black. Black with white border/white with black border?

[+slx]

11 hours ago, tf_hh said:

Are there ROMs/EPROMs installed? The RAM PCB covers the lower sockets. I suggest there was a TOS 2.06 adapter PCB with CPU sitting in the CPU´s socket. So if no ROM/EPROMs inserted, you need such a TOS-card or re-install standard ROMs for TOS 1.0x.

 

The upper CPU socket is heavily oxydized, remove and exchange it complete. The little PCB between is the blitter correction part, it must be present.

 

The GLUE and MMU are made by IMP... these ones are best known as trouble maker. The chances are high that you never get a real stable system with these.

 

if there´s no ROMs and no TOS-card, check for more modifications. Maybe somebody has removed expansions like OverScan ST, which require cutting of traces.

 

Thanks for the hints. I will check and report back. Sounds like I was little bit too curious and should better have left that machine were it was.... I didn't know you also know your way around STs.

5 hours ago, snarkdluG said:

Clean or change sockets if necessary. Reseat MMU and Glue. Clean with IPA both socket and chip. 

 

Get a test cartridge and see if you get anything on screen. Otherwise hook up a null-modem cable to other computer when booting with test cartridge. 9600 baud.

 

Probably some RAM chip or something to do with RAM that has broken. But I'm just guessing here.

 

By the way, is there anything on the screen now? All white/all black. Black with white border/white with black border?

Thanks as well. Right now the screen remains black, there is no signal at all. I do have an ST to VGA adapter to test it on another screen.