Intellivision II Troubleshooting Guide

Mattel's Figure 6: the Intellivision II power supply board, with test points TP1 to TP8 along its connector strip and their expected readings.

Fault-finding for the Intellivision II, model 5872, following Mattel's service manual. Mattel's order is: run the diagnostic test cartridge and replace any IC it names; if that does not cure the fault, or the cartridge will not run, work through the flowchart (AC adapter, power supply, clocks, bus control signals), then the symptom guide. The chip numbering differs from the original Intellivision (model 2609), whose tables do not apply to this console. Disassembly and care are on Intellivision II General Maintenance.

Preliminary checks

Before opening the console

Symptom	Probable cause	Action
Screen blank	Automatic blanking after about five minutes without input, or the intermission code (1 and 9 together)	Press any key on either controller
Snowy screen, no game	Television on the wrong channel, switch box set to TV, coax unplugged, console off	Match the television to the channel switch on the back of the console; set the switch box to GAME; check connections
White-grey screen, or one colour	Cartridge not fully inserted	Reinsert the cartridge
Buzzing or distorted sound	Fine tuning, strong broadcast signal	Adjust fine tuning; disconnect the aerial from the switch box
Console does not switch on	AC adapter	Unplug it from the console and measure 16–20 V AC between the centre and outer sleeve of its plug; replace it if the reading is wrong
One game misbehaves	Cartridge	Try the customer's cartridge, then a known-good one; if the fault follows the customer's cartridge, the cartridge is faulty

Some cartridges do not run on any Intellivision II because Mattel changed the internal executive ROM: a few early Coleco titles and Mattel's Electric Company Word Fun are affected. Rule that out before suspecting the console.

Flowchart checks

Mattel's troubleshooting procedure, in order:

1. Check the AC adapter. Unplug it from the console, plug it into a 120 V 60 Hz outlet, and measure 16–20 V AC between the centre and the outer sleeve of its plug. If not, replace the adapter.
2. Check the control line. With the console off, TP8 should read about +21 V DC. Pressing the reset button S1 should pull it to 0 V. If the +21 V is missing, remove S1; if it still does not appear, check for shorted traces between S1 and the power supply board, then replace the power supply board. If TP8 does not go to 0 V with S1 pressed, replace S1.
3. Check the crystal oscillator. Measure 7.15909 MHz at about 4 V peak to peak at TP9. If it is missing, replace crystal X1, check C17 and C16, and replace U10 with a known-good one.
4. Check the colour clock. Measure 3.579545 MHz at 4 V p-p at TP10. If it is missing, remove the STIC (U4): if the signal then appears, replace U4; if not, check for shorted traces and replace U10.
5. Check the bus control signals without a cartridge. Remove any cartridge and check the waveforms at TP15 (BC1), TP16 (BC2) and TP17 (BDIR), pressing reset every few seconds so they do not stop. If they are wrong, replace U1, then U2, then U9. If they are right, check TP18 (BC1 OUT), TP19 (BC2 OUT) and TP20 (BDIR OUT); if those are wrong, check for broken or shorted traces and bent pins at the cartridge socket J1, and replace U9.
6. Check the power supply, as described in the next section.
7. Check the 1.789772 MHz clocks. Measure 1.789772 MHz at 5 V p-p at TP11 and TP12; if it is wrong, replace U4, U2, U9 or U3 in that order. Then measure 1.789772 MHz at 10 V p-p at TP13 and TP14; if it is wrong, replace U1, then U9.
8. Check the bus control signals with a cartridge. Plug a cartridge in and check TP21 (BC1 IN), TP22 (BC2 IN) and TP23 (BDIR IN). If they are wrong, recheck TP18 to TP20; if those are right, check the cartridge socket and the cartridge (on a known-good console); if not, replace U4, then U6.
9. If the fault remains, go to the symptom guide.

Power supply

Power supply board test points (measure against TP3)

Test point	Expected
TP1 to TP2	16–20 V AC (adapter input)
TP3	Ground
TP4	−2.10 to −2.40 V DC
TP5	+5.45 to +5.95 V DC
TP6	+11.5 to +12.5 V DC
TP7	+4.85 to +5.15 V DC
TP8	Control: about +21 V DC off, +5 V DC on, 0 V with reset pressed

Readings from Mattel's Figure 6 and flowchart. On the logic board schematic the supplies arriving from the power supply board are labelled +5 V, +12 V, +5.7 V and −2.25 V.

1. Open the console far enough to see the power supply board on the logic board, and plug in a known-good AC adapter.
2. Measure 16–20 V AC across TP1 and TP2. If it is missing, check the AC jack, C38, C39, the fuse F1 and the traces from the jack to the power supply board; if they are good, replace the power supply board. The fuse is 2.0 A (part 0089-0115).
3. Press and release reset within 2 seconds. TP8 should then read about +5 V DC. If it does not, check that the reset button is not making intermittent contact, then fit a known-good power supply board. If the fault remains with a good board fitted, it is on the logic board.
4. Measure TP4 to TP7 against TP3. If any is out of range, fit a known-good power supply board; if the reading is still wrong, the fault is on the logic board.

Mattel's manual does not go inside the power supply board: it is a single part (5872-9539), and the manual gives no schematic or component list for it. See the Intellivision II Capacitor Replacement Guide for what is known about its parts.

Symptom guide

Model 5872 symptoms, causes and remedies

Symptom	Probable cause	Action
Snow, with or without the test pattern	Console not switching on	Go through the power supply checks
	Fuse blown	Check F1 on the logic board and replace it if open. If the new fuse blows quickly, check the power supply board outputs; if they are correct, look for shorted parts or traces on the logic board
	Modulator supply	If pin 2 of the RF modulator is not about +6 V DC, check R7 and C18
	RF modulator	Connect a known-good modulator in parallel, move the RF cable to it and touch the two cases together; if the picture clears, replace the modulator
	+12 V supply	Check the +12 V supply and its distribution on the logic board
Grey-white screen, no flash when reset is pressed	Clock circuit	Work through flowchart steps 3 and 4
	5.7 V supply to the STIC	Measure 5.7 V DC at STIC (U4) pin 20; if absent, trace the 5.7 V supply on the logic board
	−2.25 V supply to the STIC	Measure at STIC pin 40; if absent, trace the −2.25 V supply on the logic board. The chart prints the expected reading as −2.5 V
Grey-white screen that flashes when reset is pressed	Cartridge not fully inserted, or a damaged socket	Reinsert the cartridge; inspect the socket for bent pins and debris
	Clock path or +5 V supply	Check the clock circuit and the +5 V supply and its distribution
	Defective IC	Run the test cartridge and replace the ICs it names. If it will not run, with a known-good test cartridge and correct voltages, replace in order U1, U2, U4, then U3 or U6
	Bus control signals	Work through the bus control steps of the flowchart
Wrong, extra or missing characters and graphics	A logic board IC, the supplies or the test cartridge	Run the test cartridge and replace any IC it names; Mattel says most graphics faults come from U2, U4, U5, U7 and U8. Check the DC voltages at each IC against the schematic
Distorted picture	Interference or test set-up	Change channel, disconnect the aerial, check the television settings
	STIC or colour chip	Substitute U4 and U10 one at a time
	RF modulator	Try a known-good modulator in parallel, as above
No sound, picture good	Sound chip U6, U3 or U9	During the audio test on the test cartridge, look for audio at U6 pin 4. If there is none, replace U6, then U9, then U3. If U6 pin 4 has audio but U9 pin 9 has none, replace U9
	RF modulator	Check for signal on the modulator's audio input, then try a known-good modulator in parallel and run the sound test
Controllers do not work	The controller	Plug in a known-good controller and run the controller test; repair the faulty one as described in maintenance
	U6 or U3, or the 9-pin connector	Replace U6, then U3; check the 9-pin connector and its traces on the logic board
	Other ICs	Replace in order U4, U2, U1, U12 and U13
Picture goes blank during the test	Cartridge or cartridge slot	Try another cartridge; check the slot
	ICs, or the reset button	Replace U1, U2 and U4 in that order; check the reset button
	Crystal X1, or debris	Tap the crystal gently and watch the picture; inspect the board for foreign material
Picture freezes	ICs, cartridge or socket	Replace in order U1, U4, U2 and U3; try another cartridge; inspect the socket
Channel switch does not change channel	Switch or modulator	Replace the switch; if that does not cure it, try a known-good modulator in parallel and switch channels
Wrong colours or no colour	Clock frequency, STIC or colour chip	Check the television controls. Measure 3.579545 MHz ± 100 Hz at U10 pin 15 and adjust C17; replace U4, then U10

Signal reference

Test points on the logic board

Test point	Signal	Expected
TP9	Crystal oscillator	7.15909 MHz, about 4 V p-p
TP10	Colour clock	3.579545 MHz, 4 V p-p
TP11, TP12	Clock	1.789772 MHz, 5 V p-p
TP13, TP14	Clock	1.789772 MHz, 10 V p-p
TP15, TP16, TP17	BC1, BC2, BDIR	Bus control waveforms (no cartridge)
TP18, TP19, TP20	BC1 OUT, BC2 OUT, BDIR OUT	Buffered bus control
TP21, TP22, TP23	BC1 IN, BC2 IN, BDIR IN	At the cartridge, with a cartridge fitted

Frequencies and amplitudes from the flowchart; the schematic prints oscilloscope traces for several of these points.

Final notes

• The Intellivision II manual has no failure code table for the test cartridge; it refers to the instructions supplied with the cartridge.
• Most remedies end with a chip substitution, and only U1, U2 and U4 are socketed. The other chips have to be desoldered.
• Mattel's rules for changing ICs: use a known-good part, observe MOS handling precautions, check orientation, and change one IC at a time.

Related pages

• Intellivision II
• Intellivision II General Maintenance
• Intellivision II Capacitor Replacement Guide
• Intellivision II Service Manual
• Intellivision Troubleshooting Guide