SY99 Floppy Disk Replacement Detail

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SY99 Disk

Adapter

		Socket adapter board
		The replacement drive used in the Yamaha replacement drive kit has a different pinout on its ribbon cable, so this tiny new board is used as an adapter. By examining this circuit board it is possible to see how the conversion from 26 pins to 34 pins (plus two pin power cable) is accomplished. First, let's compare the 26 and 34 pin connectors:

26-way Floppy Ribbon	/=active low
Pin No.	Signal Name	Description
1	VCC	VCC +5V
2	/INDEX	Index
3	VCC	VCC +5V
4	/DRVS	Drive Select
5	VCC	VCC +5V
6	/DSKCHG	Disk Change
7	RES	Reserved
8	READY	Ready
9	MEDIA	Media
10	/MOTE	Motor Enable
11	/REDWC	Density Select
12	/DIR	Direction
13	RES	Reserved (In Use)
14	/STEP	Step
15	GND	Ground 0V
16	/WDATE	Write Data
17	GND	Ground 0V
18	/WGATE	Write Gate
19	GND	Ground 0V
20	/TRK00	Track 00
21	GND	Ground 0V
22	/WPT	Write Protect
23	GND	Ground 0V
24	/RDATA	Read Data
25	GND	Ground 0V
26	/SIDE	Side 1 Select

34-way Floppy Ribbon /=active low

Pin No. Signal Name Description

1 GND Ground 0V

2 /REDWC Density Select 1=Low, 0=High

3 GND Ground 0V

4 N/C -

5 GND Ground 0V

6 N/C -

7 GND Ground 0V

8 /INDEX 0=Index

9 GND Ground 0V

10 /MOTEA Motor Enable 0=Drive 0

11 GND Ground 0V

12 /DRVS1 Dirive Select 1

13 GND Ground 0V

14 /DRVS0 Drive Select 0

15 GND Ground 0V

16 /MOTEB Motor Enable 0=Drive 1

17 GND Ground 0V

18 /DIR 0= Direction Select

19 GND Ground 0V

20 /STEP 0= Head Step

21 GND Ground 0V

22 /WDATA Write Data

23 GND Ground 0V

24 /WGATE Floppy Write Enable, 0= Write Gate

25 GND Ground 0V

26 /TRK00 0= Track 00

27 GND Ground 0V

28 /WPT 0= Write Protect

29 GND Ground 0V

30 /RDATA Read Data

31 GND Ground 0V

32 /SIDE1 0= Head Select

33 GND Ground 0V

34 /DSKCHG S1= Disk Change, 0= Ready

By compairing the functional names, it is possible to see how the same controls are passed across the two interfaces. Note that the 26 pin socket has VCC present, and so only one ribbon cable is required. For a 34 pin socket, then no VCC is present, and so a separate cable needs to be made to provide VCC +5V, and Ground to the floppy drive. This is the extra white non-IDC socket that you can see on the adapter board above.
NOTE: these pinouts should make it very clear that it is NOT possible to connect a 34 pin floppy drive directly into a 26 pin socket (or vice-versa) - and doing this could damage both the SY99 and the floppy drive.
It is now possible to construct a table showing which pins to connect to which pins to make an adapter (pins are split into functional groups):

Yamaha XS051 Adapter PCB /=active low X=NO /=active low

Signal 26-way Pin No. Linked? 34-way Pin No. Signal

VCC +5V 1 X 1 Ground 0V

VCC +5V 3 X 3 Ground 0V

VCC +5V 5 X 5 Ground 0V

Reserved 7 <-> 7 Ground 0V

MEDIA 9 <-> 9 Ground 0V

/REDWC 11 <-> 11 Ground 0V

Reserved 13 <-> 13 Ground 0V

GND 15 <-> 15 Ground 0V

GND 17 <-> 17 Ground 0V

GND 19 <-> 19 Ground 0V

GND 21 <-> 21 Ground 0V

GND 23 <-> 23 Ground 0V

GND 25 <-> 25,27,29,31,33 Ground 0V

/INDEX 2 <-> 8 /Index

X 10 /Drive Select 0

/DRVS 4 <-> 12 /Drive Select 1

/DSKCHG 6 X

/MOTOR ENABLE 10 <-> 16 /Motor On

/DIR 12 <-> 18 /Direction Select

/STEP 14 <-> 20 /Step

/WDATA 16 <-> 22 /Write Data

/WGATE 18 <-> 24 /Write Gate

/TRK00 20 <-> 26 /Track 00

/WPT 22 <-> 28 /Write Protect

/RDATA 24 <-> 30 /Read Data

/SIDE1 26 <-> 32 /Side Select

READY 8 <-> 34 /Ready

VCC +5V 1,3,5 X Separate cable and connector VCC +5V

Ground Many X Separate cable and connector Ground 0V

		After having done all this investigative work, this table was then compared with the Yamaha adapter board supplied with the replacement Yamaha drive, and it appeared to be identical. It was then tested by a volunteer in Russia (successfully!)... I then found this link from FM-Alive's web-site, which serves as validation - Note: this link downloads a zip file containing a Word file, which some users may not be able to read easily...
		Useful background information 34 pin floppy disk drive connector details 1 34 pin floppy disk drive connector details 2 26 pin floppy disk drive connector details other 26 pin floppy disk drive connector details 26 pin floppy disk drive connector - warning about power pins PC Motherboards connectors FM-Alive web-site - info on classic FM synths

Note:

This is my own description of what I did with my SY99, and is shown here as an illustration of how an ex-service engineer approaches this type of task. If you attempt to make an adapter or adapter board of any kind then you do so entirely at your own risk. You should only attempt this type of activity if you are suitably qualified, and confident of your ability to complete the task successfully. I am not suggesting that you should make these modifications at all - I am merely documenting my hardware and providing a hypothetical example.

These pages are not authorised or endorsed by Yamaha in any way. You should always refer any servicing enquiries to your local Yamaha Dealer, or your country's Yamaha Service Department.

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