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Section 0

Service Manual: Service Diagnostics

During the auto tune routine, each of the 16 oscillators and filters are checked and tuned. This happens whenever the Chroma is turned on, when the [AUTO TUNE] switch is used or if a reset occurs. The eight Dual Channel Boards in the Chroma are labelled "0" through "7." (See Disassembly: Figure 3-3 for board locations.) The computer will automatically turn off any Dual Channel Board that malfunctions and display an error message in the Data Readout. The message [ERR 6], for example, means that Dual Channel Board number "6" failed and has been turned off. Subsequently pressing [AUTO TUNE] will not affect the disabled board. The computer will ignore this Dual Channel until a reset or power-up occurs. The Chroma will operate normally, but with two less channels.

There are easily accessed hidden functions available by pressing [SET SPLIT] then a numbered switch on the right panel. While many of these are outlined in the owner's manual, certain ones are most useful in diagnosing problems.

[SET SPLIT] [6] Battery Test

Displays the non-volatile memory battery voltage in the Data Readout window. A typical reading displays [cell 3.16]. When the reading drops below 2.5 volts, the two "AA" size batteries on the Computer Board should be replaced.

[SET SPLIT] [7] Disable Channel Board

This may be used to manually turn off a Dual Channel Board. If a channel board malfunctions, but was not automatically turned off during auto tune, it can be disabled manually. Play the keyboard until you hear the bad note, then while holding the key down (before playing another note) press [SET SPLIT] [7]. The channel board will turn off and be displayed as an error message in the Data Readout.

[SET SPLIT] 8] Display Disabled Boards

If a channel board has been disabled, the Chroma will operate normally with two less channels. Selecting programs or editing will cause the Data Readout to display relevant data in place of the error message. To display the number of any disabled boards, use this function.

[SET SPLIT] [9] Tapper On/Off

Alternately turns the Tapper off and on.

[SET SPLIT] [10] Cassette Mode

Selects automatic (motor sensing) or manual cassette mode. If the cassette will not load, this is the first thing to try - it may be in the wrong mode. The normal mode senses and controls the cassette motor, providing the polarity is such that the tip of the remote jack on the cassette recorder is positive in respect to the sleeve. The alternate mode allows use with cassettes that have no motor control, i.e. no remote jack.

[SET SPLIT] [26] Mute A

Suppose you hear a bad note while playing up scale on the keyboard. Before turning it off with [SET SPLIT] [7], try muting all the "A" channels using [SET SPLIT] [26]. Now only the "B" channels will function. If a channel still outputs a bad note, it will, of course, be a "B" channel. Now you may hold down the bad note, turn it off with [SET SPLIT] [7] and read the board number in the Data Readout. You will have pinpointed the malfunction down to a single channel on a single board.

[SET SPLIT] [27] Mute B

Turn off all "B" channels, similar to Mute A.

[SET SPLIT] [29] Mute All

When using Mute A or Mute B, the "A" or "B" channels are silenced by turning off the "A"-VCA or the "B"-VCA through the sample and hold circuitry. "Mute All" differs in that the oscillators (both "A" and "B") are disconnected from the filters but the filters and amplifiers can still function. This lends itself to helping you differentiate between an oscillator and a filter problem. After determining a bad note is coming from a single channel on a single board you may use [SET SPLIT] [29] to mute all oscillators. A continuing bad sound suggests problems in the filters or more remotely in the amplifiers. No sound indicates the bad note was produced by the oscillator circuitry.

[SET SPLIT] [28] Unmute

Unmute channels. This unmutes [SET SPLIT] [26], [27] and [29].

[SET SPLIT] [30] Test LEDs

Turns on all LEDs and display segments. This will provide maximum load to the Power Supply. Use this for checking a suspected marginal supply and for testing the LEDs. Select a program to restore normal operation.

[SET SPLIT] [31] Special Reset

It is possible to use some of the previously described functions to pinpoint an offending note only if the bad note plays. What if it was turned off automatically by the computer during an auto tune routine? No problem, use [SET SPLIT] [31] Special Reset. This will reset the main computer and call up an auto tune routine but the computer is instructed to ignore any channels that malfunction. This will permit you to listen to all channels, even bad ones and to apply the previously described functions to help diagnose the problem. Additionally, this function orders an ascending channel assignment from board "0" to "7" with oscillator "B" first then oscillator "A." For example: if parameter "1" is set to value "0" (individual oscillators), the first note played will be channel board "0" oscillator "B," the second note will be channel board "0" oscillator "A" and so forth to the sixteenth note which will be channel board "7" oscillator "A." With parameter "1" set to value "1" (paired oscillators), the first note will be channel "0" both oscillators "B" and "A" and the eighth note channel "7" both oscillators "B" and "A."

See note on the Parameter Chart page.

[SET SPLIT] [50] Reset

This acts as a computer reset. It calls up an auto tune routine but differs from the [SET SPLIT] [31] Special Reset by ordering a descending channel assignment and the computer is not instructed to ignore malfunctions. The computer will automatically turn off malfunctioning boards. The descending channel assignment causes the first note to play oscillator "B" on board "7" the second note oscillator "A" on board "7" and the sixteenth note, oscillator "A" on board "0," providing you have selected the 16 channel mode with parameter "1" and no channels have been turned off automatically by the computer.

Power Down/Power Up

By turning off the Chroma and turning it on again, you will initiate a complete system reset. This calls up an auto tune routine, provides automatic fail/pass channel control to the computer but differs from previous resets by activating the power supply reset circuitry. The supply reset locks out the CMOS RAM (program memory) by deactivating the chip select lines until all supplies are in regulation. Further, the power down cycle deactivates these chip select lines prior to the supplies dropping out of regulation. Should you have problems relating to loss of program memory or overwriting garbage into program memory, be sure to check the power supply reset line during power down/power up.

In diagnosing Chroma problems, you will undoubtedly find a scope useful. Unfortunately, the strobe signals in the Chroma are fast pulses and may occur only once, depending on the system routine. The scope must be set up using a triggered sweep. An easy way to obtain correct sweep settings is to use the write tapper strobe on pin 7 of Z41, on the I/O Board. Sequentially, press a right panel membrane switch as you adjust the sweep, to capture the write tapper strobe. Each time you press the membrane switch, a write tapper strobe is generated. Once the sweep is set correctly, you can "look" for other strobes as dictated by the problem at hand. The I/O strobe decoder is a good place to start in most cases. If you are looking at the write timer mode line with a scope, you may see that this write strobe is repeated 2.5us apart. This was done to get around a ground noise problem that cropped up in some early units. Pretend there is only one strobe pulse for the point of view of analysis. Also, you may notice that the timer mode bits come out of latch Z42 with the middle bit inverted. This was a p.c. layout error that was easier to correct in the computer firmware. The computer thinks it is using modes 2, 3, 0, 1 and 6; but the three latch outputs will show modes 0, 1, 2, 3 and 4.

Listed below are values of supply current in two columns. The nominal current draw is measured under maximum load using [SET SPLIT] [30]. The other column lists the maximum current the supply will deliver before current limiting occurs. Calibration and checkout of the supply voltage levels are covered in Calibration and Checkout.

Supply Nominal Maximum
+5V analog 125 milliamps 250 milliamps
+5V digital 2.3 amperes 2.5 amperes
+12V analog 500 milliamps 700 milliamps
-12V analog 500 milliamps 700 milliamps