PLA Replacement Options - Revision history

Josh at 13:39, 22 January 2026

2026-01-22T13:39:48Z

← Older revision		Revision as of 14:39, 22 January 2026
Line 8:		Line 8:
	Because original spare parts are scarce and almost forty years old, several replacement families have appeared. They differ in technology, power draw, compatibility and cost.		Because original spare parts are scarce and almost forty years old, several replacement families have appeared. They differ in technology, power draw, compatibility and cost.

	== 🔍 Selection criteria ==		== Selection criteria ==
	{\| class="wikitable"		{\| class="wikitable"
	! Criterion !! Why it matters		! Criterion !! Why it matters
Line 21:		Line 21:
	\|}		\|}

	== 🗂️ Replacement families ==		== Replacement families ==
	=== 1. Salvaged original MOS ceramic PLAs ===		=== 1. Salvaged original MOS ceramic PLAs ===
	* Perfect electrical fit if tested good, but still run hot and may fail again.		* Perfect electrical fit if tested good, but still run hot and may fail again.
Line 54:		Line 54:
	* Excellent edge-rate but enormous current draw; avoided except as teaching tools.		* Excellent edge-rate but enormous current draw; avoided except as teaching tools.

	== 🛠️ Installation ==		== Installation ==
	# Power off & unplug PSU; discharge by pressing the power switch several times.		# Power off & unplug PSU; discharge by pressing the power switch several times.
	# Gently remove the original PLA from socket '''U17''' using a PLCC puller or flat tool.		# Gently remove the original PLA from socket '''U17''' using a PLCC puller or flat tool.
Line 64:		Line 64:
	## Run a fast-loader cartridge or Dead Test to exercise all decode paths.		## Run a fast-loader cartridge or Dead Test to exercise all decode paths.

	== ⚖️ Comparison summary ==		== Comparison summary ==
	{\| class="wikitable"		{\| class="wikitable"
	! Solution !! Cost !! Heat !! Cartridge compat. !! Availability		! Solution !! Cost !! Heat !! Cartridge compat. !! Availability
Line 79:		Line 79:
	\|}		\|}

	== 📚 Further reading ==		== Further reading ==
	* Raymond Carlsen, “PLA Failures and Substitutes”		* Raymond Carlsen, “PLA Failures and Substitutes”

	[[Category:Commodore 64 Modifications and Enhancements]]		[[Category:Commodore 64 Modifications and Enhancements]]
	[[Category:Commodore Systems]]		[[Category:Commodore Systems]]

Josh: /* ⚖️ Comparison summary */

2025-04-24T12:57:18Z

⚖️ Comparison summary

← Older revision		Revision as of 13:57, 24 April 2025
Line 69:		Line 69:
	\|-		\|-
	\| Salvaged MOS \|\| High \|\| 🔥🔥🔥 \|\| ✅ \|\| declining		\| Salvaged MOS \|\| High \|\| 🔥🔥🔥 \|\| ✅ \|\| declining
			\|-
	\| EPROM TTL \|\| Low \|\| 🔥🔥 \|\| ⚠️ mixed \|\| DIY only		\| EPROM TTL \|\| Low \|\| 🔥🔥 \|\| ⚠️ mixed \|\| DIY only
			\|-
	\| GAL20V8 \|\| Low-mid \|\| 🔥 \|\| ✅ \|\| open-source		\| GAL20V8 \|\| Low-mid \|\| 🔥 \|\| ✅ \|\| open-source
			\|-
	\| CPLD/FPGA (e.g. PLAnkton) \|\| Mid (15–25 €) \|\| ❄️ \|\| ✅✅✅ \|\| multiple stores		\| CPLD/FPGA (e.g. PLAnkton) \|\| Mid (15–25 €) \|\| ❄️ \|\| ✅✅✅ \|\| multiple stores
			\|-
	\| TTL array \|\| High (parts) \|\| 🔥🔥🔥 \|\| ✅ \|\| niche		\| TTL array \|\| High (parts) \|\| 🔥🔥🔥 \|\| ✅ \|\| niche
	\|}		\|}

Josh: Created page with "The original '''MOS 906114-01 Programmable Logic Array (PLA)''' in early C64 board revisions (ASSY 326298 → 250466) is _the_ single highest-failure-rate part in the machine. It runs hot (≈ 65 °C surface on an un-ventilated bread-bin), consumes ≈ 120 mA, and any internal electrical overstress manifests as: * '''Black screen / no border''' on power-up. * Colour-flashing “garbage” that crashes after warm-up. * Selective cartridge or bank-switch errors (E..."

2025-04-24T12:56:47Z

Created page with "The original '''MOS 906114-01 Programmable Logic Array (PLA)''' in early C64 board revisions (ASSY 326298 → 250466) is _the_ single highest-failure-rate part in the machine. It runs hot (≈ 65 °C surface on an un-ventilated bread-bin), consumes ≈ 120 mA, and any internal electrical overstress manifests as: * '''Black screen / no border''' on power-up. * Colour-flashing “garbage” that crashes after warm-up. * Selective cartridge or bank-switch errors (E..."

New page

The original '''MOS 906114-01 Programmable Logic Array (PLA)''' in early C64 board revisions (ASSY 326298 → 250466) is _the_ single highest-failure-rate part in the machine.
It runs hot (≈ 65 °C surface on an un-ventilated bread-bin), consumes ≈ 120 mA, and any internal electrical overstress manifests as:

* '''Black screen / no border''' on power-up.
* Colour-flashing “garbage” that crashes after warm-up.
* Selective cartridge or bank-switch errors (EXROM/GAME decoding faults).

Because original spare parts are scarce and almost forty years old, several replacement families have appeared. They differ in technology, power draw, compatibility and cost.

== 🔍 Selection criteria ==
{| class="wikitable"
! Criterion !! Why it matters
|-
| '''Timing accuracy''' || PLA outputs must meet a < 60 ns access window to avoid VIC-II bus contention; marginal parts work in BASIC but fail with fast cartridges.
|-
| '''Voltage tolerance & heat''' || Lower idle current (≤ 20 mA) keeps internal case temperature down and avoids over-loading the 5 V rail. PLAnkton, for example, dissipates < 0.2 W compared with ≈ 0.6 W for the ceramic MOS part.
|-
| '''Board compatibility''' || 250469 “short-board” machines integrate the PLA inside the 251715-01 gate-array; external plug-ins are '''not''' required there.
|-
| '''Cartridge support''' || Fast loaders (Epyx FastLoad, KFF, EasyFlash) depend on tight /CASRAM and /ROML asserts — earlier EPROM-based substitutes can break these.
|}

== 🗂️ Replacement families ==
=== 1. Salvaged original MOS ceramic PLAs ===
* Perfect electrical fit if tested good, but still run hot and may fail again.
* Short supply & rising price (US $40–80 on auction sites).

=== 2. '''EPROM + TTL glue''' (first-generation DIY) ===
* EPROM (27C512/27C256) programmed with PLA truth-table, gated by 74LS04/74LS86.
* Cheap but '''slow''' output edges and ~65 mA current → will over-heat inside a closed case.
* Timing marginal with some Ocean/AR II cartridges.

=== 3. '''GAL / PAL-based''' (PLA20V8, ThED PLA20V8, “128 PLA in C64”) ===
* Single GAL20V8 or ATF22V10C, pin-compatible.
* Draw ≈ 20 mA, emit little heat.
* Open-source JEDEC; hobbyists can burn their own chips.
* Slightly higher propagation delay than CPLD, but passes timing on > 99 % of boards in field reports.

=== 4. '''CPLD / FPGA-based''' (current gold standard) ===
{| class="wikitable sortable"
! Replacement !! Logic core !! Idle current !! Notable points
|-
| '''SuperPLA V3''' || Xilinx XC9536XL || ≈ 15 mA || Earliest “plug-and-play” commercial part, wide PAL/NTSC & cartridge compatibility. 20 € PCB kit.
|-
| '''U17 PLAnkton''' || Altera MAX CPLD || < 10 mA || Eight-layer µPCB nestled inside a plastic SIL socket; runs cool & supports C16/+4 PLAs via jumper.
|-
| '''RealPLA / “Ultimate PLA”''' || Lattice ispMACH 4064 || 12 mA || Shipped with _Ultimate-64_ boards; cartridge timing verified with Kung-Fu Flash & Epyx.
|-
| '''SaRuMan-64''' || iCE40LP384 FPGA || ~ 8 mA || Adds a tiny linear-drop regulator to isolate noisy 5 V rails; user-upgradable bit-stream.
|}

=== 5. '''Multi-chip TTL recreations''' (educational) ===
* 27 × 74LS/AHC gates that implement the PLA equations.
* Excellent edge-rate but enormous current draw; avoided except as teaching tools.

== 🛠️ Installation ==
# Power off & unplug PSU; discharge by pressing the power switch several times.
# Gently remove the original PLA from socket '''U17''' using a PLCC puller or flat tool.
# Visually inspect the socket for oxidation or lifted pads.
# Align the notch or pin-1 indicator on the replacement with the board silk.
# Firmly press straight down — do '''not''' rock side-to-side.
# Power on and test:
## BASIC screen appears → `PRINT FRE(0)` returns 38911.
## Run a fast-loader cartridge or *Dead Test* to exercise all decode paths.

== ⚖️ Comparison summary ==
{| class="wikitable"
! Solution !! Cost !! Heat !! Cartridge compat. !! Availability
|-
| Salvaged MOS || High || 🔥🔥🔥 || ✅ || declining
| EPROM TTL || Low || 🔥🔥 || ⚠️ mixed || DIY only
| GAL20V8 || Low-mid || 🔥 || ✅ || open-source
| CPLD/FPGA (e.g. PLAnkton) || Mid (15–25 €) || ❄️ || ✅✅✅ || multiple stores
| TTL array || High (parts) || 🔥🔥🔥 || ✅ || niche
|}

== 📚 Further reading ==
* Raymond Carlsen, “PLA Failures and Substitutes”

[[Category:Commodore 64 Modifications and Enhancements]]
[[Category:Commodore Systems]]