Editing Atari Mega STE Troubleshooting (section)

== Motherboard — No Boot ==

=== White/Blank Screen ===

A blank screen on the Mega STE has similar causes to the [[Atari Mega ST Troubleshooting|Mega ST]] but with additional considerations:

# '''Verify PSU outputs''' — +5 V and +12 V within spec at the motherboard power connector.
# '''Check 16 MHz oscillator''' — the Mega STE's main clock is a 32 MHz crystal divided to 16 MHz (or 8 MHz in compatibility mode). Verify 16 MHz at the CPU clock pin.
# '''Check /RESET line''' — should pulse low on power-on (~100–200 ms) then go high.
# '''Check /HALT line''' — if held low, the CPU has halted due to a bus error.

=== GLUE and MMU Custom Chips ===

The Mega STE uses revised GLUE and MMU gate arrays that support 16 MHz operation. These are surface-mount custom Atari parts and are not field-replaceable without specialised equipment.

* '''GLUE failure:''' No video sync, no bus arbitration. The machine appears completely dead despite good power.
* '''MMU failure:''' RAM not accessible. CPU halts immediately after reset.

Both are rare failures but can occur from ESD damage or voltage transients.

=== TOS ROM ===

The Mega STE shipped with TOS 2.05 or TOS 2.06 in ROM. These are specific to the Mega STE / TT030 family and are '''not interchangeable''' with 520ST/1040ST TOS ROMs.

<templatestyles src="Template:StyledTable/styles.css" />
{| class="wikitable styled-table" style="width:100%; text-align:center;"
|+ '''TOS ROM Fault Table'''
|-
! Symptom !! Possible Cause !! Recommended Action
|-
| White screen, no activity || ROM not detected; bad contact in ROM sockets || Remove, clean pins with IPA, reseat firmly
|-
| Corrupted desktop or garbled text || Partially failed ROM; bit-rot in mask ROM || Test with known-good TOS 2.06 set. Consider EPROM replacement
|-
| Boot to desktop but crashes on GEM operations || Incompatible TOS version installed || Verify correct TOS version for Mega STE (2.05 or 2.06 only)
|}

=== RAM (30-pin SIMMs) ===

The Mega STE uses 30-pin SIMMs in groups of four. Mismatched SIMMs, incorrect speed ratings, or failed modules will cause boot failures.

<templatestyles src="Template:StyledTable/styles.css" />
{| class="wikitable styled-table" style="width:100%; text-align:center;"
|+ '''RAM Fault Table'''
|-
! Symptom !! Possible Cause !! Recommended Action
|-
| No boot, no video || All SIMM banks failed or absent || Verify SIMMs are seated. Try with a single bank of 4 matched SIMMs
|-
| Random crashes, data corruption || Marginal SIMM; speed too slow for 16 MHz operation || Use 80 ns or faster SIMMs. Test each SIMM individually in a known-good slot
|-
| Incorrect RAM count reported || Mismatched SIMM sizes in a bank || All four SIMMs in a bank must be identical capacity
|-
| Boot at 8 MHz but crash at 16 MHz || SIMMs too slow (> 100 ns) || Replace with 80 ns or 70 ns SIMMs
|}