Weird 1050 mod

[cx2k]

So, I was going through some old 1050 drives that I recently picked up. One of them had a wire and 2 position switch coming out of the opening for the on/off switch.

 

I figured it was a write-protect switch of some sort.

 

Anyway, upon opening it, I found a small 14 pin chip that had the markings scraped off and "1050" marked on it. This chip was sitting on top of 74LS74A chip as shown in the picture. All of the pins from top chip were making contact with 74LS74A underneath it. Pins 11 & 12 of top chip have wires attached which go to the 2 position switch.

 

Switch has 3 legs and I assume that the 2 positions are either side shorted to center leg. However, unless the switch is bad, only one position shorts one side to center - and the wires are hooked to the center and the side that never shorts so if the idea was to open/close the short on pins 11 & 12, that never happens as is. They're always open.

 

Anyway, would love to know if one of the experts here has ever seen this or can figure out what shorting those pins would do.

 

Thanks,

John

Edited November 9, 2018 by cx2k

[Kyle22]

I'll need to look at the schematic, but with that stock ROM, they couldn't be doing much.

[DavidMil]

Were any/all of the pins except pins 11 and 12 soldered to the 74LS74 or was it just sitting on top of the 74LS74?

 

David

[vitoco]

I lost my bad sector generator schematics many years ago, so I can't be sure, but it looks like one of them.

 

Why do you say that the switch could be bad and always open? BTW, some switches connects the center to the pin at the left when the stick is pointing to the right (the reverse to sliding switches).

[cx2k]

DavidMil - All of the pins were making contact. I hesitate to say soldered because it basically popped off like it was just sitting on top of the 74LS74. But even pins 11 & 12 were connected to the 74LS74 even though they also have a switch soldered to them. See pic below.

 

vitoco - the switch has 3 poles (left, center and right) the wires from pin 11 & 12 go to center and one side. My impression would be that you throw the switch and close the circuit between pins 11 & 12. Well, no matter which position the switch is in, those 2 pins never short out. Tested with a meter, so assume the switch is bad.

 

 

[_The Doctor__]

I've seen this before right down to the way the circles are around the numbers on the chip.. did you try some moisture to see if you could read through the roughness?

 

I almost bet this is already in one of the threads here. not soldered or in a socket sounds very strange...

[vitoco]

74LS74 is a FlipFlop chip, and pins 11 and 12 are clock and data respectively, so connecting them together with the switch should give unpredicted results in the output Q and !Q (not Q) so I bet that this mod is for write bad sectors to disks by corrupting the checksums or something in the sectors while writing them. Some local pirates used that type of copy protection technique... I wrote a copier for myself while my drive had the mod. Happy and US Doubler mods were rare in my country by those years.

 

About your test of the switch, did you cut the cables from the switch? If the chip was already connected to the pins, you could get an unpredicted lecture in your tester. Try to test directly to the pins 3 and 2, which are clock and data respectively for another flipflop in the same chip. What did you get there?

[DavidMil]

Are there any marking on the outside of the case that might indicate that this was a drive a company owned? The way this looks to me, it might

have been an in-house device possibly used with different drives.

 

David