Orphaned Machines need help

[vizfizz]

Hi Everyone,

 

Just picked up some orphaned machines today.

 

1st is a Mega ST 2 or 4. Not sure. Badge says Mega ST 4, serial number sticker says Mega ST 2. Anyway.. no biggie. Anyway, the machine seems to be functioning normally, however, I can't get it go down to Medium or Low rez modes. I'm using a Best Electronic's cable into a NEC 1970nx which works great with my 1040 STE and the second orphaned machine...but the Mega says nope. Any ideas why?

 

The second machine is a 1040 STf. This machine seems to have a flakey floppy. Turn on the machine and the desktop comes up without floppy drive icons. However, turn on the machine with a disk in the drive and tadah... floppy drive icons. Read and Write however is 50/50. Sometimes it works, sometimes it flakes out and says there's a problem with the disk. (Which there isn't....the disk works fine on all other machines). So... course of action? Just replace the drive or can the drive be saved?

 

The 1040 also has several busted keys...broken all the way down. Can I use a keyboard from a 1st gen 520ST and put it in the 1040? I have a couple laying around.

 

Finally... both machines are filthy and yellowed beyond belief. What's your favorite retrobrite formula?

 

Thanks everyone!

 

 

[vizfizz]

Ok... update on the Mega ST.

I opened up the case and low and behold I found that this is not a "true" Mega ST 4. It is a Mega ST 2 that had a Z-RAM upgrade put into it. In my opinion the installation was done reasonably well, but who ever did it taped down the pin-grid board onto the MMU with a ton of duck tape. The motherboard is coated with 20 year old crusty glue. Some still sticky, some hardened solid. After examining this particular upgrade...it basically pulls the shifter chip out of the motherboard and a daughter board is inserted into that chip bracket... then the shifter is transplanted to the Z-RAM daughter board. Then a ribbon cable attaches to a pin-grid board that sits on top of the MMU and is taped down to ensure it remains in place. That's it.

My guess is that the shifter has been damaged in the process. I removed the Z-RAM upgrade and re socketed the shifter into the motherboard's socket. I turned on the machine and high resolution is still available, but low rez and medium rez will not activate when attached to a low rez capable monitor. My theory is the shifter is incapable of going into color modes because its been damage somehow from the Z-RAM installation. Since the original owner only used a monochrome monitor, he never knew of the problem.

Does anyone know if older 520's or 1040's use the same shifter? I could try a transplant.

Edited September 4, 2016 by vizfizz

[ParanoidLittleMan]

Same as in other post - clean floppy heads, whole drive as first.

Keyboards on early STs - with separated PSU and floppy drive and later integrated ST, STE models have different connectors.

Considering non working low and med res: you should check is there some shortcut on monochrome sensor line - starting at monitor connector. High res activates when that pin is shorted to GND. What is done with cable, of course.So, you need to check that with Ohm-meter, or just measure voltage of that pin, or where leads (get schematic) with voltmeter. Must be min 3V in color modes.

[vizfizz]

Bummer on the keyboard swap. Guess I'll try pulling keys and plastic key connectors from the old 520 keyboard rather than the thing.

 

You may be right about the monitor connector. The Best Electronics ST VGA monitor cable works in color for my 1040 STE, the 1040 STf and the MSTE so the cable seems fine.

 

So to check the voltage of that pin...you're referring to the monitor connector right? I need to get a volt meter to test it. I just need to know where to test. Gotta find schematics.

[ParanoidLittleMan]

Keys aren't separate parts, only in some Mega STE or TT keyboards - where whole kb. is separated too

Look where mouse/joystick connectors are placed ...

[vizfizz]

Perhaps I wasn't clear. The machine with the broken keys is the 1040stf. MSTE and Mega keyboards are ok. Each key on the 1040 keyboard is held in place by a plastic connector underneath that holds the key in place. Several of these connectors are broken and no longer hold keys. ill need to replace these or just get a new keyboard all together. Ah well. Needs to be done.

[ParanoidLittleMan]

Here in Europe we don't say ever "plastic connectors". Connector is something what leads electricity. I guess that you mean plastic part what is under key cap. That would be connector in some very generous way - under it is rubber with some graphic to make shortcut when key is pressed. And that thing moves, so main function is not to hold cap, but to make contact when key is pressed. It's really hard to follow when someone describes like that. Atlantic sea is pretty much wide .

But I can post you those plastic/graphic parts or whole ST keyboards (have 2 lying around) if you want. Only that shipping cost could be somehow wide too

And I guess that printed circuit board under rubber/plastic is broken too, most likely. I knew guy who made such damage couple times when was very mad

[vizfizz]

Here in Europe we don't say ever "plastic connectors". Connector is something what leads electricity. I guess that you mean plastic part what is under key cap. That would be connector in some very generous way - under it is rubber with some graphic to make shortcut when key is pressed. And that thing moves, so main function is not to hold cap, but to make contact when key is pressed. It's really hard to follow when someone describes like that. Atlantic sea is pretty much wide .

But I can post you those plastic/graphic parts or whole ST keyboards (have 2 lying around) if you want. Only that shipping cost could be somehow wide too

And I guess that printed circuit board under rubber/plastic is broken too, most likely. I knew guy who made such damage couple times when was very mad

 

Ok.. after a good night's rest (not), I got back on this. The 1040STf with the broken keys has been fixed. I salvaged several of keys and their clip holders from an old 520 and all is well. You were right that I "wasn't thinking" regarding the 520's keyboard. Different connector and I forgot about joystick port position. (How can any 1040 st user forget that!) But anyway... keyboard problems fixed.

 

Now for the 1040 STf's floppy drive. I swapped it out with another 720k drive. That worked perfectly (though its not the right form factor. I have the diagonal long eject button and the drive I used was a small short button) However it proved to me that its not the 1040STf. The faulty drive works some of the time. If you boot with a disk in the drive, I'll get drive icons and a 50/50 success rate of reading a disk. If I boot without a disk, I'll never get drive icons on the desktop. So I believe the solution is a drive replacement. What do you think?

 

Then there's the Mega ST2's issues. I took out a functioning 1040 STf shifter chip and replaced it with the shifter from the Mega. The result? The 1040 STf operated normally. I could access all resolutions and color modes on the Nec 1970NX via the Best Electronic's cable. This suggests to me that the Mega's shifter chip is operating normally and that there's something else going on inside the Mega ST2 that's faulty.

 

I placed the Mega's shifter back into the motherboard and I could still only access high resolution mode. So... what would be the likely course of action next? Test the monitor port's connectivity? Or could there be a problem with a different chip on the motheboard?

Edited September 4, 2016 by vizfizz

[ParanoidLittleMan]

There is mono detection line on video connector - called mono on, pin 4. It leads to MFP chip 68901. As suggested, you need to check is it on high level when color, or no monitor connected. No need for some logic analyzer as some smarthead suggested on other forum. There may be some shortcut to GND on that line, or pull-up resistor is broken. Of course MFP chip may be faulty too. Shifter will be set in color or mono mode according to what is at mono on line. So, starting with replacing it was bad idea.

[vizfizz]

Ok. I will check the mono on pin with a friend of mine that has the meter/probe. I tried swapping the shifter because it was the only course of action I had without a meter. But I will do what you suggest on the next pass.

[Zogging Hell]

Is the drive single sided, quite possible if it is a big button number? In that case it will fail everytime you try and read a double sided disk. The drive belt on these models may also have degraded to point it is slipping as well if so may cause intermittent failures. The belt can be replaced - see ebay - but if it is single sided it isn't going to be much use.

[vizfizz]

It's a big button model but not single sided. Definitely DD 720k.

[themrfreeze]

The drives with the wide angular eject button were made by Chinon and known for their unreliability. Replacing faulty Chinon drives with something like an Epson (with the small rectangular eject button) was relatively common back in the day (I know I replaced a few myself). Requires modification of the top case though.

 

I dug my 520ST out of the attic a few weeks ago and the Chinon in the SF354 external drive was faulty. I have a few Epsons that work, but wound up installing a Lotharek SD card floppy emulator instead. Works great.

[vizfizz]

The drives with the wide angular eject button were made by Chinon and known for their unreliability. Replacing faulty Chinon drives with something like an Epson (with the small rectangular eject button) was relatively common back in the day (I know I replaced a few myself). Requires modification of the top case though.

 

I dug my 520ST out of the attic a few weeks ago and the Chinon in the SF354 external drive was faulty. I have a few Epsons that work, but wound up installing a Lotharek SD card floppy emulator instead. Works great.

 

Definitely the plan for this particular 1040STf. I have a number of machines that I am refurbishing and retrofitting. SD cards and USB drives seem the way to go.