WD1002A-27X Troubleshooting - Page 1
Forum section: electronics / general

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 18, 2024, 10:11:56 pm
content: PCB photos for posterity:https://www.seventransistorlabs.com/Images/WD1002A-27X_Top.jpghttps://www.seventransistorlabs.com/Images/WD1002A-27X_Bot.jpgAm having something of an issue between it and a drive... dunno what the deal is. ST238R seems to work fine: tested it by bit-banging signals by hand, spins up, seeks, homing is a little scuffed but seems to work, data pours out... Can't decode the raw data of course.Meanwhile, this card, BIOS and DOS don't say anything bad about it, no POST errors; but neither does the drive manifest, no C: drive, no partition, no MBR, no invalid system disk, boot looks for A: immediately.Poking at a somewhat lower level, INT 13h does understand a hard drive 0 (drive number 80h) but it doesn't seem to respond to commands; most operations return an error code.Haven't seen an exact manual for it, though this seems close:https://www.minuszerodegrees.net/manuals/Western%20Digital/WD1002S-WX2%20-%20OEM%20Manual.pdfwill try the Ex series in a bit.Tim

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: October 19, 2024, 10:47:00 pm
content: Beats me, but what is this?

author: Ian.M
author_rank: Super Contributor
timestamp: October 20, 2024, 02:41:40 am
content: Its a late IBM XT era hard disk controller,ST412HPdrive interface compatible, with on board BIOS ROM, to run two RLL rated drives.Seehttps://theretroweb.com/expansioncard/documentation/20216.pdfNote the use of MSDOS DEBUG to access the low level format routine in its BIOS.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 20, 2024, 02:42:31 am
content: Inductor, molded I think. Unusual lead form. That chip seems to be "data separator", so, PLL, clock recovery, RLL de/encoding.The L1, L2 bottom-left, on... GND/+5V I think?, are also strange; black on top, red on the sides. I guess those are ferrite beads. Molded? Painted?Neither style is something I've seen these days; the ceramic caps are also a bit unusual in the range of colors, and all with low aspect ratio (but then, 0.1uF's in 1206s aren't very thick anyway).The 1210 below R101 is also kinda odd looking. Just translucent enough to see the electrode shading? Kinda random.Resistors very normal looking with respect to modern parts.Tim

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: October 20, 2024, 02:43:09 am
content: To me it looks upside down?

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: October 20, 2024, 02:44:01 am
content: Quote from: Ian.M on October 20, 2024, 02:41:40 amYes, I know, I added an arrow to an odd-looking component (to me).

author: Ian.M
author_rank: Super Contributor
timestamp: October 20, 2024, 04:41:53 am
content: Ah, I missed the arrow.However the pages I found documenting the card jogged my memory of this type of 8 bit PC bus controller - IIRC as the PC BIOS didn't natively support hard discs, everything was handled by the card's BIOS extension ROM, and as battery backed CMOS (+RTC) to store system settings like hard disk parameters wasn't introduced until the IBM AT, it is likely that drives that haven't previously been used with a WD1002A-27X card wont work with it unless the drive is initialised so it can be recognised, by entering the card's BIOS with DEBUG and configuring the drive parameters there. I believe the configuration was stored on the drive on track 0.

author: Sorama
author_rank: Frequent Contributor
timestamp: October 20, 2024, 07:39:45 am
content: Quote from: Alex Eisenhut on October 20, 2024, 02:44:01 amIt is an inductor.Look at the naming too.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: October 20, 2024, 10:45:36 am
content: Quote from: Sorama on October 20, 2024, 07:39:45 amYes. It looks upside down. Why would the solder contacts be on top, as well as the little mold mark?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 22, 2024, 03:43:30 pm
content: Surprisingly, the datasheet is online:https://bitsavers.computerhistory.org/components/westernDigital/_dataSheets/WD10C22B_Self-Adjusting_Data_Separator_1988.pdfIt's probably L102 (p.5). Gotta love that short circuit to GND (below L101)...Tim

author: coromonadalix
author_rank: Super Contributor
timestamp: December 10, 2024, 05:49:18 pm
content: this is the picture of one on ebaythe inductor is colored in bandsand on others sales, we do see the inverted part on L101 ? weird