Asking for assistance for PS/2 386SX owners on Real Time Clock

[alejack12001]

The machine I am addressing with this post is an IBM PS/2 Model 8555 386SX computer. The machine powered up once several weeks ago for a brief time with errors. Briefly the errors were date, time, floppy, and display. With this post, I wish. To address the real time clock. When this machine was built, its clock was the Dallas clock on chip. Dallas clocks are either difficult to get or they come from China. The one I have is the Dallas DS1287 probably from China. The Dallas is too large for the socket that exists on the motherboard. This socket is directly below the ROM chips. The Dallas has two pins hanging off either end of the socket.

I then saw the advertisement by Necroware for a designed RT clock where the battery can be replaced. The nwx287 RTC Real Time Clock with a small CR1220 battery is what I used on my motherboard to bring for a short period of time the machine back to life. Since that time the machine has not returned to life; I think it might be the floppy drive error. I will post a separate thread on that subject later. I got more batteries for the Necroware. The RT Clock seems to drop the voltage of the battery even though the machine is not in use. Over a week’s time the voltage dropped from 3.3 Volts to 3.0 volts. I am unsure how long these batteries would last over an extended period of time.

I am seeking what other PS/2 owners did with regard to the RT Clock.

 

[GiGaBiTe]

Coin batteries will flatten out at 3.0v for the majority of their useful life, it's not unusual to see them floating around that voltage. The Dallas clock chip may drain a battery like a CR1220 quicker than a CR2032 though. I think I remember seeing some Dallas chips being depotted having two batteries inside them in parallel to increase the battery capacity. But you're still looking at several years of run time with a single battery.

As for the floppy drive not working, you probably need to recap the drive. The floppy drives and the hard drives in PS/2 machines are known for leaking capacitors that cause them to stop working.

 

[johnx993]

I have a PS/2 used a 'smart terminal' for my other vintage machines.
I recapped the drives already.
And I found a Dallas clock replacement, but when I installed it, it asked me to load the install/configuration disk, which I do not have.
So... I removed it as just live with hitting F1 during the boot cycle.
But as I said, it has a single purpose, and not really kept as a 'vintage' machine in it's own right. (perhaps it should be)
-J

 

[alejack12001]

Coin batteries will flatten out at 3.0v for the majority of their useful life, it's not unusual to see them floating around that voltage. The Dallas clock chip may drain a battery like a CR1220 quicker than a CR2032 though. I think I remember seeing some Dallas chips being depotted having two batteries inside them in parallel to increase the battery capacity. But you're still looking at several years of run time with a single battery.

As for the floppy drive not working, you probably need to recap the drive. The floppy drives and the hard drives in PS/2 machines are known for leaking capacitors that cause them to stop working.

I saw the Necroware video on his refurbishment of the Model 8555 386SX where the floppy caps were replaced. While his caps were replaceable using his method. I have a physical issue with essential tremor's in my hands that make holding and directing a soldering iron a real challenge; not impossible, but, the probability of error is very high.

The Model 8555 386SX uses a 40-pin floppy controller built into the motherboard. IBM made everything with this model computer perpirtory. The recommended floppy for this model by Electronic Pocket Reference Manual is the part number 64F0162 floppy drive made by Mitsubishi, similar to the one Necroware repaired in his video. This floppy has a 34-pin connection similar but not the same as commercial such as Teac or Sony 1.44 floppy drives. This difference is the connection between the 40-pin and the 34-pin. IBM used a special part numbered 27F4912 cable, which was replaced by 27F4668 because of RF problem with the 27F4912. Finding this cable on the web is impossible. At first, i read on the web an adapter could be used to convert the signals for the 40-pin to 34-pin connector made by Tex Elec as shown in the enclosed picture. I had to make a 40-pin female edge connector to connect this adapter to a commercial floppy. Unfortunately the adapter didn't work. In fact the machine wouldn't turn on, not even the fan until I took this adapter out then the fan back on.

I made a table of the pin arrangements for comparison as shown below. There are voltages passed on a pin by pin basis except for pins 35-40. The pins that are of concern are pins 1 and 4. Pin one shows a reserved setting that would be grounded and pin four is a setting defining the drive type, which is not addressed by the 40-pin connection.

Lastly, my approach is to cut the last 6-pin cable wires and connect the remaining 34-pin ribbon cable wires to the floppy to see if it responds; barring the fact that the caps might be bad.

40-pin Planer Model 8555		34-pin 76x6063 Model 8555 Floppy Drive
Pin	Connection		Pin	Connection
1	Reserved		1	Ground
2	Hiigh Density Select		2	Hiigh Density Select
3	5-Volts		3	5-Volts
4	Reserved		4	Drive Type. ID 1
5	Ground		5	Ground
6	12-Volts		6	12-Volts
7	Ground		7	Ground
8	Index		8	Index
9	Ground		9	Ground
10	Reserved		10	Reserved
11	Ground		11	Ground
12	Drive Select		12	Drive Select
13	Ground		13	Ground
14	Reserved		14	Reserved
15	Ground		15	Ground
16	Motor Enable		16	Motor Enable
17	Ground		17	Ground
18	Direction		18	Direction
19	Ground		19	Ground
20	Step		20	Step
21	Ground		21	Ground
22	Write Data		22	Write Data
23	Ground		23	Ground
24	Write Enable		24	Write Enable
25	Ground		25	Ground
26	Track 0		26	Track 0
27	Ground		27	Ground
28	Write Protect		28	Write Protect
29	Ground		29	Ground
30	Read Data		30	Read Data
31	Ground		31	Ground
32	Head 1 Select		32	Head 1 Select
33	Ground		33	Ground
34	Diskette Change		34	Diskette Change
35	Ground
36	Ground
37	Reserved
38	5-Volts
39	Ground
40	12-Volts

 

[alejack12001]

I have a PS/2 used a 'smart terminal' for my other vintage machines.
I recapped the drives already.
And I found a Dallas clock replacement, but when I installed it, it asked me to load the install/configuration disk, which I do not have.
So... I removed it as just live with hitting F1 during the boot cycle.
But as I said, it has a single purpose, and not really kept as a 'vintage' machine in it's own right. (perhaps it should be)
-J

Take a look at this link for downloadable reference disk: Reference disk the disk is an image of PC DOS 5 and the means to configure the machine using 1.44 floppy boot disk. I haven't been able to do this because of the floppy issues on my machine. But if you research some of the youtuber's who have setup their PS/2's and you'll see what the reference disk will display once it boots up.