IBM 3270 PC Troubleshooting Guide: Difference between revisions

Line 150:

# If POST passes but Control Program fails, verify CP version against model.

# If Control Program loads but host connection fails, check the BNC cable and the 3174/3274 controller.

== ⚠️ Power-supply RIFA capacitor and tantalum shorts ==

Two age-related failures are near-universal on this era of IBM hardware:

* '''RIFA mains-filter capacitors''' in the power supply are metallised-paper parts that crack and fail '''short''' with age, producing acrid smoke shortly after power-on. Replace them pre-emptively with modern X2-class parts.<ref name="ibm_rifa">[https://www.minuszerodegrees.net/failure.htm minuszerodegrees.net — IBM failure symptoms]; [https://www.classic-computers.org.nz/blog/2010-11-04-restoring-an-IBM-xt.htm Repairing and Restoring an IBM XT]; and [https://retrorepairsandrefurbs.com/2025/05/15/1983-ibm-pc-5160-xt-power-supply-rebuild-modifications/ Adam's Vintage Computer Restorations]. Source for the RIFA mains-filter capacitor failing short (smoke) and the tantalum capacitors failing short and preventing the PSU from firing.</ref>

* '''Tantalum capacitors''' on the planar (system board) and on ISA cards fail short with age. A shorted tantalum will '''prevent the power supply from starting''' (dead machine, PSU protection latched) — look for a cracked or discoloured tantalum and lift suspect ones to find the short.<ref name="ibm_rifa">[https://www.minuszerodegrees.net/failure.htm minuszerodegrees.net — IBM failure symptoms]; [https://www.classic-computers.org.nz/blog/2010-11-04-restoring-an-IBM-xt.htm Repairing and Restoring an IBM XT]; and [https://retrorepairsandrefurbs.com/2025/05/15/1983-ibm-pc-5160-xt-power-supply-rebuild-modifications/ Adam's Vintage Computer Restorations]. Source for the RIFA mains-filter capacitor failing short (smoke) and the tantalum capacitors failing short and preventing the PSU from firing.</ref>

IBM PC/XT switching supplies also need a '''minimum load''' to start, so a bare supply on the bench may not run without a dummy load.<ref name="ibm_rifa">[https://www.minuszerodegrees.net/failure.htm minuszerodegrees.net — IBM failure symptoms]; [https://www.classic-computers.org.nz/blog/2010-11-04-restoring-an-IBM-xt.htm Repairing and Restoring an IBM XT]; and [https://retrorepairsandrefurbs.com/2025/05/15/1983-ibm-pc-5160-xt-power-supply-rebuild-modifications/ Adam's Vintage Computer Restorations]. Source for the RIFA mains-filter capacitor failing short (smoke) and the tantalum capacitors failing short and preventing the PSU from firing.</ref>

== POST beep and error codes ==

The IBM Power-On Self Test signals faults by beeps and, where a display works, by a numeric code:

{| class="wikitable styled-table" style="width:85%; text-align:left;"

|+'''IBM POST beep codes'''

! Beeps !! Meaning

|-

| 1 short || Normal POST — system OK

|-

| 2 short || POST error (numeric code shown on screen)

|-

| No beep || Power supply or system-board fault

|-

| Continuous / repeating short || Power supply or system board

|-

| 1 long, 1 short || System-board fault

|-

| 1 long, 2 short || Display-adapter fault (MDA/CGA)

|-

| 1 long, 3 short || Display-adapter fault (EGA/later)

|}

Common numeric codes include '''161/163''' (dead CMOS battery/clock), '''201''' (memory), '''301''' (keyboard) and '''1701''' (hard disc). A code ending in the family prefix identifies the failing subsystem.<ref name="ibm_post">[http://o-r-b.nl/modificaties/beeb_codes.htm Standard Original IBM POST Error Codes]; and [https://www.ibm.com/support/pages/troubleshooting-post-beep-and-no-beep-errors IBM — POST beep errors]. Source for the IBM POST beep and numeric error codes.</ref>

== References ==

== Related Pages ==

@@ Line 150: / Line 150: @@
 # If POST passes but Control Program fails, verify CP version against model.
 # If Control Program loads but host connection fails, check the BNC cable and the 3174/3274 controller.
+== ⚠️ Power-supply RIFA capacitor and tantalum shorts ==
+Two age-related failures are near-universal on this era of IBM hardware:
+* '''RIFA mains-filter capacitors''' in the power supply are metallised-paper parts that crack and fail '''short''' with age, producing acrid smoke shortly after power-on. Replace them pre-emptively with modern X2-class parts.<ref name="ibm_rifa">[https://www.minuszerodegrees.net/failure.htm minuszerodegrees.net — IBM failure symptoms]; [https://www.classic-computers.org.nz/blog/2010-11-04-restoring-an-IBM-xt.htm Repairing and Restoring an IBM XT]; and [https://retrorepairsandrefurbs.com/2025/05/15/1983-ibm-pc-5160-xt-power-supply-rebuild-modifications/ Adam's Vintage Computer Restorations]. Source for the RIFA mains-filter capacitor failing short (smoke) and the tantalum capacitors failing short and preventing the PSU from firing.</ref>
+* '''Tantalum capacitors''' on the planar (system board) and on ISA cards fail short with age. A shorted tantalum will '''prevent the power supply from starting''' (dead machine, PSU protection latched) &mdash; look for a cracked or discoloured tantalum and lift suspect ones to find the short.<ref name="ibm_rifa">[https://www.minuszerodegrees.net/failure.htm minuszerodegrees.net — IBM failure symptoms]; [https://www.classic-computers.org.nz/blog/2010-11-04-restoring-an-IBM-xt.htm Repairing and Restoring an IBM XT]; and [https://retrorepairsandrefurbs.com/2025/05/15/1983-ibm-pc-5160-xt-power-supply-rebuild-modifications/ Adam's Vintage Computer Restorations]. Source for the RIFA mains-filter capacitor failing short (smoke) and the tantalum capacitors failing short and preventing the PSU from firing.</ref>
+IBM PC/XT switching supplies also need a '''minimum load''' to start, so a bare supply on the bench may not run without a dummy load.<ref name="ibm_rifa">[https://www.minuszerodegrees.net/failure.htm minuszerodegrees.net — IBM failure symptoms]; [https://www.classic-computers.org.nz/blog/2010-11-04-restoring-an-IBM-xt.htm Repairing and Restoring an IBM XT]; and [https://retrorepairsandrefurbs.com/2025/05/15/1983-ibm-pc-5160-xt-power-supply-rebuild-modifications/ Adam's Vintage Computer Restorations]. Source for the RIFA mains-filter capacitor failing short (smoke) and the tantalum capacitors failing short and preventing the PSU from firing.</ref>
+== POST beep and error codes ==
+The IBM Power-On Self Test signals faults by beeps and, where a display works, by a numeric code:
+<templatestyles src="Template:StyledTable/styles.css" />
+{| class="wikitable styled-table" style="width:85%; text-align:left;"
+|+'''IBM POST beep codes'''
+! Beeps !! Meaning
+|-
+| 1 short || Normal POST &mdash; system OK
+|-
+| 2 short || POST error (numeric code shown on screen)
+|-
+| No beep || Power supply or system-board fault
+|-
+| Continuous / repeating short || Power supply or system board
+|-
+| 1 long, 1 short || System-board fault
+|-
+| 1 long, 2 short || Display-adapter fault (MDA/CGA)
+|-
+| 1 long, 3 short || Display-adapter fault (EGA/later)
+|}
+Common numeric codes include '''161/163''' (dead CMOS battery/clock), '''201''' (memory), '''301''' (keyboard) and '''1701''' (hard disc). A code ending in the family prefix identifies the failing subsystem.<ref name="ibm_post">[http://o-r-b.nl/modificaties/beeb_codes.htm Standard Original IBM POST Error Codes]; and [https://www.ibm.com/support/pages/troubleshooting-post-beep-and-no-beep-errors IBM — POST beep errors]. Source for the IBM POST beep and numeric error codes.</ref>
+== References ==
+<references />
 == Related Pages ==