Data East/Sega

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1 Introduction

Data East/Sega pinball used a board set with minor differences from 1987 to 1995. This boardset, like most hardware of this generation, is very derivative of Bally/Williams System 11 hardware.

Data East Standard DMD Board Set, this from a Star Wars

The following boards are typical of what you will find in a Data East backbox.

• RED - Power Supply
• BLUE - CPU
• YELLOW - Playfield Power Board
• GREEN - Sound Board

There can also be two additional boards, not including satellite boards which were used such as a shaker motor driver board, a magnet control board, etc.

• Games with solid state flippers will have a flipper control board name the TY-FFASI board. This board is located on the left side of the lower cabinet. Games which have more than three flippers, Baywatch and others, use two flipper control boards.
• Display controller boards are mounted behind the displays. DMD controller boards have a separate CPU and communicate to the main CPU via a ribbon cable.

2 Games

For an extensive list of games produced by Data East and Sega, see the List of Data East Games.

The following table lists regular production games based on their circuit board (PCB) and system generations.

Game List and Board Version
Game (Manufacture Date)	CPU	Power Supply	PPB	Display	Sound	Flipper	Notes
Laser War (3/87)	520-5003-01 or 520-5003-02	520-5000-00	520-5015-00	2x 7 digit A/N, 2x 7 digit N, 1x 4 digit N		No PCB 3 lug coil and EOS switch
Secret Service (2/88)	520-5003-02	520-5000-00	520-5015-00	2x 7 digit A/N, 2x 7 digit N		No PCB 3 lug coil and EOS switch
Torpedo Alley (8/88)	520-5003-02	520-5000-00	520-5021-00			No PCB 3 lug coil and EOS switch
Time Machine (11/88)	520-5003-02	520-5000-00	520-5021-00	1x16 digit A/N 2x 7 digit N		No PCB 3 lug coil and EOS switch
Playboy 35th Anniversary (5/89)	520-5003-02	520-5000-00	520-5021-00
ABC Monday Night Football (9/89)	520-5003-02	520-5000-00	520-5021-00
Robocop (01/90)	520-5003-02	520-5000-00	520-5021-00
Phantom of the Opera (4/90)	520-5003-02	520-5000-00	520-5021-00
Back to the Future (6/90)	520-5003-03	520-5000-00	520-5021-00
The Simpsons (10/90)	520-5003-03	520-5000-00	520-5021-02	2x 16 digit A/N 520-5030-00	520-5002-03-12	520-5033-00
Checkpoint (2/91)	520-5003-03	520-5047-00	520-5021-00	128x16 DMD 520-5042-00			First pinball machine with a DMD display
Teenage Mutant Ninja Turtles (6/91)	520-5003-03	520-5047-00	520-5021-00	128x16 DMD 520-5042-00
Batman (8/91)	520-5003-03	520-5047-00	520-5021-00	128x16 DMD 520-5042-00
Star Trek (9/91)	520-5003-03	520-5047-00	520-5021-00	128x16 DMD 520-5042-00
Hook (5/92)	520-5003-03	520-5047-00	520-5021-00	128x16 DMD 520-5042-00
Lethal Weapon 3 (8/92)	520-5003-03	520-5047-01	520-5021-00	128x32 DMD 520-5052-00			First DE usage of 128x32 display
Star Wars (12/92)	520-5003-03	520-5047-01	520-5021-00	128x32 DMD 520-5052-00
Rocky & Bullwinkle (2/93)	520-5003-03	520-5047-01	520-5021-00	128x32 DMD 520-5052-00
Jurassic Park (6/93)	520-5003-03*	520-5047-02	520-5021-05	128x32 DMD 520-5052-00	520-5050-02	520-5033-02	Motor Control board mounted under playfield
Last Action Hero (10/93)	520-5003-03*	520-5047-02		128x32 DMD 520-5052-00
Tales from the Crypt (12/93)	520-5003-03*	520-5047-02		128x32 DMD 520-5052-00
The Who's Tommy (1/94)	520-5003-03*	520-5047-02		128x32 DMD 520-5052-00
WWF Royal Rumble (5/94)	520-5003-03*	520-5047-02		128x32 DMD 520-5052-00		520-5080-00 (2 used)
Guns N' Roses (7/94)	520-5003-03*	520-5047-02		128x32 DMD 520-5052-00
Maverick (10/94)	520-5003-03*	520-5047-03		192x64 DMD 520-5075-00			First usage of 'super' 192x64 display
Mary Shelly's Frankenstein (1/95)	520-5003-03*	520-5047-03		192x64 DMD 520-5075-00
Baywatch (2/95)	520-5003-03*	520-5047-03		192x64 DMD 520-5075-00		520-5080-00 (2 used)
Batman Forever (7/95)	520-5003-03*	520-5047-03		192x64 DMD 520-5075-00

* Extra pins at CN3 for printer. See the CPU section for more information.

3 Technical Info

Data East used several different board generations. It is important to be able to identify the different versions when performing diagnosis and testing.

3.1 CPU

• 520-5003-01

• 520-5003-02

Data East 520-5003-02 CPU Board from Time Machine

• 520-5003-03

3.2 Power Supply

Data East made several revisions to their power supplies during production to support different displays and flipper combinations.

3.2.3 520-5047-01

Rev A and B High Voltage section:

• Has no resistor R17
• The Zener diode at D10 is a 1N4764 and is tied to ground
• Zener diode D11 is a 1N4743
• Connector CN7 has three pins for unregulated 12 volts

Rev C of the -01 board has the same changes to the high voltage section as the -02 version below.

3.2.4 520-5047-02

Differences from the high voltage section of 520-5047-01 Revision A and B:

• Has a resistor at R17
• The Zener diode at D10 is a 1N4743
• The Zener diode at D11 is a 1N4764 tied to ground
• Connector CN7 has five pins for unregulated 12 volts vs. the -01 version having three pins.

The -02 power supply is backwards compatible to machines that use the -01 power supply.

3.3 Display Board

• 520-500x-00 Master Display

Slave Boards

520-5004-00

520-5005-00

520-5006-00

520-5007-00

• 520-5014-01

• 520-5030-00

• 520-5042-00 - Used for the 128x16 line dot matrix displays on games Checkpoint through Hook.
• 520-5052-00 - Used for the "standard" sized 128x32 line dot matrix displays on games Lethal Weapon 3 through Guns N' Roses.
• 520-5075-00 - Used on the large 192x64 dot matrix displays on games Maverick through Batman Forever.

3.4 Sound Board

• 520-5002-0x series
  • 520-5002-00
  • 520-5002-02
  • 520-5002-03

• 520-5050-0x series
  • 520-5050-01
  • 520-5050-02
  • 520-5050-00
  • 520-5050-03

• 520-5077-00 - This board is similar to the 520-5050-0x series. It was redesigned to allow up to four 27040 EPROMs for voices and sound effects. It has a different pre-amplifier design than the 5050 series, but uses the same MB3730A power amplifiers.
  

Sega 520-5126-02 sound Board (Front)

Sega 520-5126-02 sound Board (Back)

• 520-5126-02 - This board is very similar to the 520-5077-00 design. The power amplifier section was redesigned. It is reported that it is interchangeable with the 520-5077-00.
  

3.5 Playfield Power Board (PPB-1)

• 50v coil board

• 520-5015-00

• 520-5021-00

Data East 520-5021-05 PPB-1 Board

• 520-5021-05
  

3.6 Flipper Board

• 520-5033-0x series
  • 520-5033-00
  • 520-5033-03

• 520-5070-00

• 520-5076-00

• 520-5080-00

3.7 Data East Diagnostics Systems

Solid state pinball machines typically have a built in system for audits and adjustments. Data East/Sega used two types of auditing systems. The first system was Ease-A-Just and was used on Laser War through Mary Shelly's Frankenstein. The Portals system was first used in Baywatch and was used for all machines after.

3.7.1 Ease-A-Just

The Ease-A-Just control panel

The East-A-Just system is very similar to the menu system in Bally/Williams System 11 machines. The control panel is located in the cabinet just inside the coin door. The forward/reverse (green) button is an up/down positional switch and the step (black) button is a momentary switch. To enter the East-A-Just system press the step button. If the green button is in the down position the game will enter the diagnostics menu. If the green button is in the up position the game will enter the audits and adjustments menu. Diagnostics are game dependent so check your game manual for specifics. All games do have a switch test with the diagnostics section that can be used to diagnose switch problems. To exit the Ease-A-Just system hold down the Step button. This will rapidly send you to the last setting and will put the game in attract mode.

Setting Free Play

Data East machines hide many adjustments under a 'Expand Adjustments' section, including the free play adjustment. To set free play enter the adjustments section of Ease-A-Just by pressing the black button while the green button is in the up position. This will put you in 'Audit' mode. Now put the green button in the down position (reverse) and press the black button (step). You are now in the adjustments section. The last adjustment is typically 'Expand Adjustments'. Change this adjustment to 'Yes' to see many more adjustments, including free play. Adjustment values are changed by pressing the game start button.

3.7.2 Portals

To be completed. A brief explaination of the Portals system is in each game manual.

4 Problems and Fixes

4.1 Fuse Clips

Data East used fuse clips on circuit boards as opposed to fuse holders. These clips are prone to cracking and causing intermittent connections. These clips cannot be repaired and should be replaced when cracked. The clips do have a correct orientation, when installing them make sure the "tabs" on the portion that grasps the fuse is oriented outwards.

Fuse clips are located on the Power supply, Playfield Power Board, and Solid State Flipper Board.

4.2 Power Driver Issues

Quickly test the TIP102/TIP122 transistors (Q8-Q13, Q23-Q30, Q39-Q46, Q72-Q79) on the MPU:

• Turn the game OFF
• Set your DMM to Ohms/Continuity buzz
• Attach the black lead to one of the metal grounding straps (crocodile clips are helpful here), there should be one in the backbox you can use
• Touch the red lead to the metal tabs of the TIP122/TIP102's
• Any that read 0 Ohms (ie are shorted) are bad and will need replacing.

You may also need to replace the predriver transistor (2n4401) that the bad transistor is connected to. It is also wise to check the wiring and the coil before powering back on, otherwise you may blow the transistor you just replaced.

See How to test a coil

4.3 PPB Board Issues

Common issues include:

• Burnt GI connector
• Dead TIP36C

4.4 MPU Boot Issues

Data East CPU Board LED Flash Sequence

Data East CPU - Location of diagnostic LEDs

Much like the Williams System 11 CPU, the Data East CPU performs a basic diagnostics procedure and produces a series of LED flashes to indicate potential boot issues. The CPU automatically tests the PIAs, RAM and EPROMs at each boot.

With all tests passed, the LEDs illuminate in the following sequence at power-on:

• The PIA and +5V LEDs illuminate immediately
• Approximately 1/2-second later the PIA led is turned off and the Blanking LED illuminates
• +5V and Blanking LEDs are illuminated until the game is turned off.
• If a failure is detected on major board components, the PIA LED will display a flash code:
  
  

PIA LED Flash Sequence
PIA LED	Suspect Component	Location
Stays On	One of the 6821 PIAs	various
Flashes 1 Time	6064 RAM	D5
Flashes 2 Times	EPROM	B5
Flashes 3 Times	EPROM	C5

4.5 Power Supply Issues

4.5.1 Low +5v

Data East CPU - 5 Volt and Ground Test Points

If you have a low +5v, you'll experience game resets, especially when pressing the flippers during multiball. A 'shotgun' repair would be to replace the bridge rectifier (DB1, CM3501), C2 (100uf 25v), C1 (1000uf 25v) and TR5 (2N6057) on the power supply board.

4.5.2 PS 520-5047-01 - High Voltage Missing at the DMD display

4.5.2.1 No +68v is found at the DMD display

Warning Be extremely careful not to touch anything when working on live High Voltage (HV) circuits.

Assuming it's not the transfomer, connectors or fuses then you should be able to measure a +DC High Voltage (HV) at the banded side of D5 with respect to GND.

If no voltage there, suspect fuses and then test D5 on the diode setting and replace D5 with a 1n4004 diode. Also test, and replace D7 with a 1n4004 diode at the same time for good measure as it's a penny part and probably stressed. Same procedure although it rectifies the a -DC HV.

Measurements are with respect to ground. You should now have a HV +DC reading at the banded side of D5. Test for +68v output. You should also have a HV -DC reading at the non-banded side of D7. Test for -100v and -98v DC output.

Do not be concerned if measured voltages are not exact without a DMD connected, they will read lower under load. It can also be that the DMD display itself is faulty and taking down the PSU.

Capacitors C10 / C11 are important, if you can't test then replace them. Especially if it looks to bulge at ends, old capacitors dry out and then fail. C10 and C11 are both 100uF @ 200v. You should be able to use 150uF at a higher voltage for these, so 150uF @250v is fine.

Observe the polarity of the capacitors you remove and mark with a Sharpie if not already indicated on PCB mask. This is very important for Electrolytic capacitors which have a polarity!

D5 / C10 are for the +68v HV DC to the DMD Display. D7 / C11 are for the -98v and -110v HV DC to the DMD Display.

The circuit for +68 voltage is comprised of components under CN5 / CN6 of the Power Board (PSU).

+68v circuit
Part	Description	Location	Eqivalent
MJE340†	NPN transistor	TR3	MJE15030
MPSA92	PNP transistor	TR1	available
1n4760b	68v zener diode	D9	available
1n5228	3.9v zener diode	D6	available
1n4004	diode 400v @ 1A	D5	available
47K	resistor 1 Watt	R8	available
330K	resistor 0.5 (1/2) Watt	R11	available
1.5K	resistor 0.5 (1/2) Watt	R12	available
500 ohm	resistor 10 Watt Ceramic	R15	available
100uF @200v	Capacitor	C10	e.g. 150uF @250v

† The MJE15030 is a heavy duty version of the MJE340 (TR3)

Check values of the above resistors. Any out of spec. (or showing open) will need to be replaced first. Test DMD again. Then replace the 1N4760 68v and 1N5228 3.9v zener diodes and test DMD again. Then work through the transistors, replacing TR1 then TR3 test the DMD.

4.5.2.2 No -100v is found at the DMD display

Follow a similar procedure to the one above. The plus and minus HV circuits are nearly 'mirror images'.

A missing -98v DC output only while reading -100v points to D11 (1n4742 12v zener diode) or R14 (4K @ 10W ceramic resistor) as faulty. Test resistor value R14 and replace if open or out of spec. Then replace D11 observing banded side for polarity.

The Circuit for -100 and -98 HV voltages are comprised of components under CN5 / CN6 of the Power Board (PSU).

-100v / -98v circuit
Part	Description	Location	Eqivalent
MJE350†	PNP transistor	TR4	MJE15031
MPSA42	PNP transistor	TR2	available
1n5379b	110v zener diode	D10	available
1n5228	3.9v zener diode	D8	available
1n4004	diode 400v @ 1A	D7	available
47K	resistor 1 Watt	R9	available
330K	resistor 0.5 (1/2) Watt	R10	available
1.5K	resistor 0.5 (1/2) Watt	R13	available
100uF @200v	Capacitor	C11	e.g. 150uF @250v

† The MJE15031 is a heavy duty version of the MJE350 (TR4)

Check values of the above resistors. Any out of spec. (or showing open) will need to be replaced first. Test DMD again. Then replace the 1N5379B 110v and 1N5228 3.9v zener diodes and test DMD again. Then work through the transistors, replacing TR2 then TR4, test the DMD. Get the -100v output working first, then go after the -98v circuit.

-98v circuit only
Part	Description	Location	Eqivalent
1n4742	12v zener diode	D11	available
4K	resistor 10 Watt Ceramic	R14	available

4.6 Switch Issues

Data East machines have switch testing built into its diagnostics. If a switch has not been activated in a while (typically 50 games) the machine assumes the switch is bad and displays a message when powered on. Sometimes this message can appear because a working switch hasn't been activated during play. You can manually activate the switch to clear this message.

Data East uses a switch matrix to control all switches except the test button switches and the special solenoid switches. A general discussion of the switch matrix is discussed elsewhere in the pinwiki.

Switches do go bad from wear and this is a typical point of failure. Here is a checklist to determine what is causing a switch failure.

1. Look to see if many switches are out, and if so see if they are all in the same row or column of the switch matrix. Your game manual will have a copy of the switch matrix specific to your machine. If several switches are inactive check for a broken wire somewhere along the path. If many switches in the same row or column are bad their is a high likelihood your issue is on the CPU board and not with the switches.
2. Make sure your switch is not shorted against itself. Check to make sure that the leads to not touch or have not been bent together and that the diode is not shorted against the common lead.
3. For microswitches, make sure the switch lever still works. You should hear a click when the level is moved and the switch is activated. You can sometimes bend the switch lever to make the switch require less travel to activate a closure. Note that these switches can still be bad when the click is audible. The best thing to do is put your machine in switch test mode and manually activate the switch. If it does not activate every time replace the switch and diode.
4. For leaf switches, make sure the two contacts are adjusted properly. You can clean the contacts with a business card by putting the card between the contacts, closing the switch, and quickly removing the card.
5. You can use a multimeter instead of the machine's built in switch test to make sure the switch works correctly. Put your DMM on the continuity setting, put one lead on the common lug (it should have the banded end of the diode) and the other lead on one of the other lugs. The continuity setting should change when the switch is activated. Move the DMM lead not on the common lug to the remaining lug. The continuity should change and work in the opposite manner.
6. Check the diodes for correct orientation and that they are connected correctly. Typically the banded end of the diode goes toward the lug farthest from the common lug. Check your game's manual to be sure. Diodes do go bad but this is unusual. 1N4001 diodes can be replaced with 1N4004 diodes.

4.7 Score Display Issues

Early Data East pinball machines used alpha-numeric score displays similar to those in Bally/Williams Machines. Data East was the first pinball manufacturer to use a dot matrix display (DMD) in a pinball machine, and had three different generations of the display. Starting with Checkpoint and running through Hook, Data East used a 128x16 score display. Williams first used the common 128x32 display in Terminator 2, and Data East soon switched to this display size for the majority of their machines, (from Lethal Weapon 3 until Guns N' Roses). Data East then switched to the larger 128x64 display. This display was used in only four Data East / Sega games including: Maverick, Frankenstein, Baywatch, and Batman Forever.

Outgassing Displays

DMDs have a lifespan and will eventually fail. It is important to replace an outgassing display because they will strain your power supply, and eventually damage that as well. Signs of outgassing displays are that areas of the display need to 'warm up' before becoming fully bright or that the display will remain completely blank for a few seconds and then appear normal.

• A side note to the display issues taking some time to light. There are cases of import machines having a circuit to delay the DMD appearing after the machine was turned on before diplaying. This was done by some operators so that serial number and location information was not shown when the machine powered on. This circuit will not damage anything but is not standard. More information about this can be found in a rec.games.pinball discussion.

4.7.1 Alphanumeric Issues

To be completed. Please contribute.

4.7.2 Dot Matrix Issues

Although Data East board designs share many similarities between Bally/Williams, the score display CPU is implemented very differently. Data East has a separate board and CPU for controlling the dot matrix display (DMD). This board is mounted behind the DMD on the score panel. The main CPU and this daughterboard communicate through a ribbon cable. Because of this, it is important that your CPU and display roms are the same version, or are in sync with each other. Running different ROM versions can cause some strange display issues. Ribbon cables are known to have faults, so reseating or swapping the cable may fix some issues.

4.7.2.1 128x16 (Small DMD) issues

The 128x16 DMD was the first DMD used in a pinball machine and was used for five games. It was replaced by the much more familiar 128x32 display.

Sometimes this display will light but the display will appear garbled. The display will flicker and move but the output will not be readable. This can be caused by the R95 resistor on the DMD controller board going out of spec. It should be a 33k 1/2 watt resistor.

4.7.2.2 128x32 (Regular DMD) Issues

The 128x32 DMD was used in the majority of Data East machines and was the only size used by Bally/Williams. The display glass is the exact same version for both Data East and Bally/Williams and can be used as a drop in replacement. However, you will still need the DMD controller board used by Data East machines.

Before and after shots of the display board after upgrading from the stock board with two 2MB ROMs. Notice the removal of the 0 ohm resistor(jumper) at R11

Some games such as Lethal Weapon 3 and Star Wars sometimes used two 27020 EPROMs at locations U12 and U14. You can use one EPROM instead if upgrading to newer code. If one EPROM is used R11 should be open (nothing installed). This part can simply be cut off the board. If two EPROMs are used, R11 should be jumpered with a zero ohm resistor or jumper wire. Why Data East called this a resistor (R11) vice a jumper, is anyone's guess. This is discussed in a service bulletin.

It is worth mentioning that if two 2MB EPROMs are used, and the R11 zero ohm jumper is not installed, the DMD will remain blank.

High voltage for the DMD is located on the PSU board.

Connection CN2 on the DMD controller board can sometimes be problematic. This is a three pin connector, and only two of the header pins are used for the +5vdc and ground. It is always a good practice to upgrade the connector pins in this housing to Trifurcon connectors. Using Trifurcon connector pins will help ensure that a more solid connection is made at CN2. Unfortunately, the existing connector housing is not reusable, and will have to be replaced when the connector pins are upgraded.

4.7.2.3 128x64 (Large DMD) Issues

The large 128x64 DMD was used in the last four Data East pinball machines. The display is a relatively expensive part to replace, costing several times as much as the more standard 128x32 DMD.

One of the most common issues with this display is that it will periodically go blank or reset the CPU. These issues are typically due to the logic power needed to drive the DMD controller board chips dropping below the required +5vdc. As Stern mentions in their service bulletin, the controller board runs at +5vdc, and "'likes' its 5 volts or darn near close". To overcome the issue, Stern offers an optional wiring harness to increase the reliability of the +5vdc logic power by pulling the +5vdc from an otherwise unpopulated connector on the power supply. A detailed discussion of the kit can be found in Stern service bulletin 106.

4.8 Flipper Issues

Data East was the first company to use solid state flippers. Starting with Playboy 35 Anniversay, Data East flippers began using a single wound coil instead of the high/low windings found in earlier games and Bally/Williams games. This design is known as the Deger design and is found in most of the Data East games. Service Bulletin #62 is a listing of flipper coil parts for Data East games and shows the evolution.

When a Data East flipper is energized, 50 volts is sent to the coil for the initial flip. The FFASI board the drops the voltage to 9 volts so that the flipper may be held up for a long period of time without burning the coil. This voltage drop occurs after 40 milliseconds, is CPU controlled, and cannot be adjusted. This differs from the Bally/Williams design where the flipper hold is determined by the End-Of-Stroke (EOS) switch and contributes to what many say is a different feel between Data East and Bally/Williams flippers.

Data East eventually did add an EOS switch to its flipper design beginning with Jurassic Park. Again this differs from Bally/Williams in that the switch is normally closed. This was done because certain game features fired the ball quickly back to the flippers. If the ball hit the flippers and moved them 1/16 of a inch the EOS switch would open and 50 volts would again be delivered to the flipper. This is discussed along with the general theory of Data East flipper operation in service bulletin #49. With this design if the hold voltage is broken and the EOS is badly adjusted, you may experience 'machine gun flippers'.

These flippers are controlled by the flipper board (TY-FFASI board) mounted in the cabinet. The board is prone to a few failures, but it's a fairly simple circuit so fixing it is normally quite easy. You should see a red LED flash when the flipper buttons are pressed.

To test the flipper board:

• Remove the board from the cabinet (it's much easier to work on)
• Check all the fuses on the board, 4 in total (2 power, 2 hold). Also check the fuse clips.
• Check all transistors using a DMM
• Check tracks for continuity and corrosion
• Replace board back into cabinet and power on game
• Enter Diagnostics (so power is sent to the flippers)
• Check voltage at coil lugs (Should be ~50v DMM set to DC, black lead on GND, red led on banded side)
• Press flipper button and check hold voltage (should be 8v)
• Check power/hold voltage on flipper board (black lead on GND, DMM set to DC, red probe on CN2-6&7 8v hold, CN2-8&9 power)

If you have no power voltage on CN2-8 and CN2-9, check the PPB board J7-1 and J7-5.

If you have no hold voltage on CN2-6 of the flipper board, check the Power Supply board CN1-10 and CN1-11. If you have no hold voltage on the coil lugs, check the hold fuses on the TY-FFASI board.

• The newer 520-5080-00 (EOS) flipper board can be modified to work in games requiring the 520-5033-00 (non-EOS) flipper board. Steps to do this can be found in Service Bulletin #103.

4.8.1 Flipper Repair and Rebuilding

Coming soon...

5 Game Specific Problems and Fixes

Please see the game specific pages for game specific problems.

6 Repair Logs

CPU Board Repair
Data East Power Supply Rebuild

6.1 Delayed or Missing Blanking Signal

Time Machine CPU board - blanking signal would go high approximately after 7 seconds or more, (if it went high at all), after PIA diagnostic signal would go low (PIA LED would go out). For a properly functioning CPU board, the blanking signal should go high immediately after the PIA signal changes its state from high to low.

Resolution: a bad AMI 6808 CPU chip. Beware of failing AMI chips. It is rumored that AMI chips have higher failure rates than most other manufacturers. This ultimately was a simple fix, but after extensive troubleshooting was performed first. This particular fix is more of an exception than the rule. Generally, a missing blanking signal should be isolated to the blanking generator circuitry (555 timer chip, 2N4403, etc.).