J7 / P7

Power Check P7
V dc Min	V dc Max	-Lead Pin	+Lead Pin
+4.8	+5.2	P7-5	P7-10
+4.5	+5.4	P7-9	P7-5
+11.5	+12.6	P7-5	P7-3
+10.8	+12.9	P7-4	P7-8

Ground is also shown as "DC RTN"

J14 / P14

Power Check P14
V dc Min	V dc Max	-Lead Pin	+Lead Pin
+4.8	+5.2	P14-1	P14-3
+4.8	+5.2	P14-1	P14-4
+4.8	+5.2	P14-2	P14-5

Ground is also shown as "DC RTN"

H032934 Intermittent, difficult-to-diagnose system problems

Intermittent and very difficult to diagnose system problems, may be caused by line cords which are not fully seated, or are too loose to make a tight connection.

When troubleshooting intermittent post errors, or any unusual, system problems, (for example; system performs power-on reset unexpectedly during operation) check the line cord for proper seating. Slight forming of the male contacts in the system unit power supply connector may correct the problem. Replacing the line cord may be necessary in some cases. Both ends of the line cord should be checked.

Peter wrote:
One reason why it might appear as dead is, when for example a monitor is placed on top of the unit and the mechanical pressure through the monitor on the top cover presses down the vertical riser-card, so that the pins at the underside of the systemboard get shorted against GND on the case. This was pretty familiar mistake one some series of Mod. 55SX.

I would recommend to remove the top cover, all MCA adapter cards and detach the harddrive cable from the riser-card and try if the system comes up again.

On some few occasions the 55SX suffers on a defective power supply, which did not send the "Power Good" signal to the board and this therefore does not come out of the pre-POST status (no reset, no Power On Self Test, all subsystems deactivated).

> A problem developed with the 55SX Power Supply. If I flip the switch the system is dead, but if I leave it that way with the power on in about 5 to 10 minutes the system will boot normally. One time starting up I got a 1XX error with a few question marks underneath. and the system crashed with a stack error System Halted, and after flipping the switch and waiting fifteen seconds the system refused to power on, but after sitting ten minutes the power came on and the fan started moving.

Stephan Goll
Hello Mike. I believe, you are right with the power supply. But there is voltage up to 1.5 kv insight, and it´s not funny to get shocked by this.  But if you try, there must be a resistor (near the high-power capacitors) inside loading a small capacitor, that supports voltage for the low-voltage powered control-electronic. May be the resistor or the cap´ (or someing else) is wrong (and that is simplified). The 55 PSU contains only one board, not that complex, but be warned. Really only for people, they know, what they do. Learned by experience. ;-|

H095558 Surge suppressors and intermittent problems

  There is no requirement for external surge suppression devices on IBM PC (Personal Computer) or Personal System/2 products. The power supplies in these systems have been designed to meet IBM corporate requirements that include factors considered adequate for product protection.

  If intermittent problems are being experienced, and normal troubleshooting efforts have failed to isolate the source of the problem, and an external "surge suppression device" is being used, try running the system without it. If the problems no longer occur, suspect the surge suppression device to be the source of the problem.

Surge suppressor facts:

  1. External surge suppression devices have been known to be the source of difficult to diagnose system problems.

  2. No universally accepted design or performance standards, such as IEEE or ANSI, have been established for these devices, therefore design and performance vary between vendors, or models.

  3. There is no practical way to test them in the field.

   4. Recent research reveals surge protectors may contribute to LAN crashes by diverting surge pulses to ground, thereby contaminating the reference used by data cabling.

  There are several surge suppression devices available on the market, however the most commonly encountered device is the MOV (metal oxide varistor). MOVs have a failure mode of "shorting" when subjected to surges beyond their peak ratings, and are subject to "MOV degradation" over time, which reduces their value as surge suppressors.