Position indicator driver boards and MicroComm data: codes, voltages and wiring

The PI and the driver’s own display use short codes to tell you where the data stopped. Use this table to decide what to check first.

On DHXXX-XMXXX or DVXXX-XMXX MicroComm displays, D can also mean that data from the driver is missing or not recognized. On EHXXX-XMXXX or EVXXX-XMXXX displays, OK or AOK can indicate the same communication problem. These are MicroComm-input models; a discrete-input dot matrix display showing D or CE has different checks. See dot matrix display troubleshooting.

The driver and display may be incompatible. A software mismatch can occur when an MCCA or SMCDU driver uses a processor marked P333 or higher and the display processor begins with M. The options are a replacement display or an MC2000 software translator board.

The same condition can occur when a MicroComm driver is connected to a non-CE display. Contact CE support or sales for help selecting a compatible replacement.

Terminal 1 is common, 2 is V+ and 3 is data. Readings should be the same at the driver and at every PI.

1. Set the meter to DC volts. Black lead on 1, red lead on 2: expect about 24–30 V DC (readings of 24.7 V, 25 V and 31 V are all acceptable; the PIs are fine as long as this is not well over 35 V).
2. Black lead on 1, red lead on 3: expect +1.5 to 2 V DC, fluctuating (1.8–2.1 V typical; 1.3–1.7 V on an MCE 2000 “skinny blue board” is acceptable).
3. If 1–2 reads about 2 V and 1–3 reads 24–25 V, wires 2 and 3 are swapped.
4. If 1–2 reads negative 24–25 V, wires 1 and 2 are swapped.
5. If 1–3 reads negative 1.5–2 V, wires 1 and 3 are swapped. This produces 2V on a car PI while the machine-room PI steps correctly; swapping 1 and 3 at the car PI fixes it.
6. Readings that are correct at the driver but wrong at the PI mean the field wiring is crossed or has a bad connection; the voltage cannot change between the two ends.

When readings are confusing, disconnect everything from the PI’s green 1-2-3 plug and run three temporary wires straight from the driver’s 1, 2, 3 to the PI’s 1, 2, 3. If the PI then works, the problem is in the building wiring. There should be only one driver per car (a separate driver may exist for hall PIs); two drivers tied to the same PI circuit will give nonsense voltages.

If a PI has a correct 24 V across 1–2 and still shows nothing — not even OK, and nothing in test mode (switch 1 on) — a component on that PI has failed. For example, a data wire that has carried 25 V to a CE3768 display means the display has to be replaced.

A socketed 51 Ω resistor sits beside the MicroComm output on the driver (marked R3 on some boards). It protects the data-drive circuit: if 24 V gets onto wire 3 (wires 2 and 3 crossed or touching), the resistor burns open instead of the board. An open resistor means no data reaches the PIs even though the driver’s own display shows the right floor.

1. Unplug the MicroComm output connector and measure 1–3 at the driver: expect 1.5–2 V DC. A reading of 0.02–0.6 V points at the resistor.
2. Pull the resistor with small needle-nose pliers and measure it. It should read about 51 Ω (give or take about 5 Ω; 50.3 Ω is a good reading). A reading of 6 MΩ is open.
3. Replace it with a 51 Ω resistor (47–56 Ω is acceptable). Make sure the new one seats fully in the socket. Both ½ W and 2 W have been quoted for this part — confirm the wattage with CE support for your board.
4. Replacing the open resistor restores communication; this also applies to a GAL-style CDPI driver (CE3448) whose PIs are stuck on A OK.

The data-protection resistor is identified as R17 on the SMCDU and R46 on the MCCA. CE’s support guidance gives a normal terminal 1-to-3 reading of approximately +1.4 to +2.2 VDC, fluctuating. If the reading is negative or fluctuates between +3 and +4 VDC, check for swapped terminals 1 and 3. If it is below +1 VDC, check the resistor with the output disconnected; if the resistor measures correctly, the driver may need repair or replacement. A reading around +8 VDC also points to the driver. If the data voltage is correct and the display still shows 2V, the display may need repair or replacement.

ZZ means the driver is not seeing any floor signal, so the first job is to prove that the controller’s outputs are reaching the harness. On a binary job the common wire carries the signal voltage and the controller pulls each active bit to the other side.

Also verify that the input voltage and polarity match the board. On an SMCDU the R1–R10 input resistors set the expected voltage; on an MCCA the corresponding resistors are R1–R13. The values in the following table are from CE’s support guidance:

Without a binary decoder, the SMCDU accepts positive or negative DC signals when the green/black and/or green/white return wires are connected correctly. For DC inputs, an MCCA must match the polarity it was built for; contact CE if the board and controller signals do not match.

For the MCCA, the second character of the part number identifies the expected signal:

1. Slide the plastic cap off the 12-pin harness plug so you can meter where the wires enter the connector.
2. Identify the wires: green/black is the common (far left), red/black is the lowest floor or bit 1, white/black is the next, then solid blue, then solid orange.
3. Measure green/black to ground (AC and DC) to learn what the controller supplies. A Motion controller may show 58 V AC, for example.
4. Measure green/black to the active bit for the floor the car is on. You should see roughly the same voltage as in step 3 on the active wire and near zero on the others. Seeing only 4–5 V AC on every bit, while each bit also reads 58 V to ground, means the controller is not pulling its outputs down — the controller outputs are not firing and the controller supplier needs to look at them.
5. If you built your own harness because the new plug is larger than the old one: the CE color code has not changed in decades, so colors should match one-for-one; an adapter is also available that mounts the small older connector onto the new larger header. Ask for it rather than splicing.
6. To prove the driver and PIs themselves are fine, turn DIP switch 1 on an SMCDU on: it scrolls through the floor set in the EPROM and every PI should follow it.

Verify with CE support.

For wire-per-floor jobs, measure from the common wire to each floor wire; the active floor should read the full signal voltage and the others near zero.

1. SMCDU harness colors: green/black = common (far left); red/black = floor 1; white/black = floor 2; solid blue = floor 3; solid orange = floor 4; solid green = floor 5; solid red = floor 6; solid white = floor 7; solid black = floor 8; orange/black = down arrow; blue/black = up arrow; green/white = second common. The two commons are tied together on the board, so green/white can be landed with green/black or left off; it only matters if the arrows use a different voltage from the floors.
2. On an MCE controller the typical landing is green/black to 2PI, red/black to 1P, white/black to 2P, blue to 3P, orange to 4P. Unused floor wires (e.g. solid green on a 4-stop job) stay unconnected.
3. With the car at the bottom floor, measure AC volts green/black to red/black; at the next landing measure green/black to white/black. On a 120 V board expect about 120 V AC on the active floor (99 V is acceptable) and well under 10 V on the others.
4. If the active floor and the others all read under 1 V, check the controller’s PI supply: 2PI should be 120 V AC hot with respect to terminal 1 (neutral). A reading of 0.8 V AC between 2PI and 1 indicates a blown fuse on 2PI.
5. A reading near 300 V AC between green/black and a floor wire is a wiring fault — unplug the harness from the board immediately before it burns components, then find the cross-connection.
6. If the common is correct but no floor wire ever shows voltage, the controller outputs are not engaging; this is a controller-side problem.
7. Some very old harnesses had the wire colors punched into the plug in reverse order. Verify at the controller terminals which colors actually land on 1P, 2P, 3P, 4P rather than trusting the colors alone.

Readings that are low but not zero also break the display: a mini PI (SMCDU with an SC015 decoder) that says OK and then blanks, or steps sporadically, may measure only 13–22 V AC (or 72 V) between decoder terminal 16 and the floor terminals where 120 V AC is expected. CE’s guideline: if 120 V is expected, anything much under 90 V means the controller output is not firing properly. A PEI showing wrong floors with 29 V AC on its floor wire has the same cause. Verify with CE support.

Yes. The input voltage is set by the row of socketed plug-in resistors near the input connector (above J5 on an SMCDU); swap them for the 24 V value.

1. For 24 V DC inputs on an SMCDU, replace the socketed input resistors with 6.8 kΩ, 2 W (color bands blue-gray-red-gold). Replace R1–R10, or at least the positions in use: floors use the low numbers (R1, R2, R3…), the down and up arrows use R9 and R10.
2. Boards shipped for 120 V AC carry 18 kΩ resistors (brown-gray-orange-gold). On 24 V signals these do not conduct enough and the PI shows a slash or never changes floor.
3. Never apply a higher voltage than the resistors are rated for. A board set for 6–20 V DC that is fed 149 V AC burns R1, R2 and R9. Its 820 Ω resistors (2 W parts in a ½ W package so they fit the socket) are only good to about 24 V DC or slightly more AC.
4. Signal polarity also matters. For dot-matrix discrete-input displays, a DH320-W0B1X expects positive-going signals; a controller that pulls its outputs to −24 V DC with a positive common needs the DH320-W0F1X (the “B” in the part number becomes an “F”).
5. When ordering any replacement driver, give CE the floor-signal voltage, whether it is AC or DC, whether it goes positive or to ground when active, binary or wire-per-floor, and the floor markings. Boards bought through a fixture supplier as stock are often configured by that supplier, so CE may have no record of the final setup.

A replacement board must match the old one in two places: the plug-in input resistors (signal voltage) and the small U4 program chip (floor set and binary vs. wire-per-floor).

1. Compare the color bands on the plug-in resistors of the old and new boards. If they differ, move the old resistors (or the correct values) into the new board — only the positions in use need to match (R1, R2, R9, R10 on a 3-stop job with arrows).
2. If the controller gives one wire per floor but the new board was programmed for binary, move the U4 chip from the old board to the new one. Otherwise you get floors 1 and 2 and then blank.
3. Keep the old board and its chips; even a board that is decades old carries the correct programming for the job.
4. On an MCCA driver with an EPROM programmed for floors B, 1–10, a car that has no basement shows “3” at floor 1 if DIP switch 6 (“0 scan slot”) is turned on. Turn switch 6 back off; the fix is an EPROM programmed for floors 1–10 from whoever did the original programming. If the controller can give one wire per floor instead of binary, the same board accepts it with no switch change: input 2 = floor 1, input 3 = floor 2, and so on.
5. Early MCCA drivers for Schindler Miconic controllers: with DIP 1 and 3 on, the driver ignores its program and shows a hex code of the inputs it sees. The top terminal of the long vertical connector should read +24 V DC to ground; with the car at floor 1 the next terminal should read 24 V against it. Terminals 1, 2 and 4 go to ground in binary fashion when active. 0 V = controller outputs not firing.

A mismatched resistor set or U4 chip is the usual cause when a replacement board gives only a slash; turning DIP 6 on shifts the floors and should be reversed.

No. Drivers such as the CE2058 (two horizontal input connectors at the bottom, three-wire output halfway up the left side, DIP 1, 2 and 3 selecting one of several programmed floor sets) have not been made for decades and will not talk to current displays — a new PI on one just shows 2V. The reverse is also true: a current driver will not drive those old PIs.

Your options:

1. Replace the driver with a current MCCA-4… driver and keep the old driver in place for the old PIs (two drivers for one car), or
2. Replace the driver and all PIs together.
3. For the new driver you must supply the floor-signal voltage (AC/DC), polarity, binary or wire-per-floor, and the floor markings.

First prove the driver is healthy: DIP 3 on, 24.68 V DC across 1–2, 1.7–2.0 V DC fluctuating across 1–3, and the removable resistor (green-brown-black bands) at 50.3 Ω. With the driver proven, the next step is to hook one display directly to the driver’s three-wire output to see whether arrows appear, then move outward into the building wiring.

Verify with CE support.

No. F is the fire-return indication. The driver shows it whenever its Message 1 input is active, so a PI flashing F/F1 during normal service means the controller is holding that input on.

1. Set all DIP switches on the driver off (normal operation).
2. Look at the small message board in the driver box. LED D1 lit = Message 1 (fire return) active; D4 lit = independent service. D1 should only be lit during actual fire return.
3. Measure DC volts between COM (far-left terminal on the green plug) and the next terminal (Message 1). 23 V DC in normal service means the signal is wrong.
4. Unplug the message-board connector: D1 goes out and the PI stops flashing. The PI still follows the car floor to floor with it unplugged.
5. Trace the Message 1 wire back to the controller. If it lands on a controller output that stays on in every mode, including fire phase 2, either the wire is on the wrong terminal or that output is stuck. Leave it disconnected until the controller side is corrected, otherwise the PI keeps flashing.

If ZZ appears on car-top/independent operation, note that ZZ normally only appears when the driver loses power and has no floor signals when it comes back.

245 V on a board built for 220 V AC input (e.g. MCCA-4F2FFFE, floor signals −24 to −48 V) is only a little high and is not what burned the diodes. The transformer steps 230 V down to about 20 V, so 245 V adds roughly 1.5 V; after the bridge and filter capacitor the 1–2 output measures about 31 V, which is acceptable as long as it stays well under 35 V. Burned diodes at the transformer plug together with two failed display boards on the same link indicate a voltage spike on the incoming power; replace the damaged parts and watch for a repeat.

Related supply problems:

• Fuse blows as soon as the board is plugged in (MCCA-X with MAMM1 on 220 V). No AC across the two orange secondary wires and none across the single white and single black primary wires, with the primary measuring 11.9 Ω, points to a bad transformer, a miswire or stray wire strands. Swap only the board (not the whole box) with a working car to isolate the board from the transformer. Verify with CE support.
• Driver for an MCE HMC 2000 blows the 4 A fuse and shows only 13 V DC at the board. The board wants about 20 V AC (up to 24 V AC or 32 V DC; 26–28 V AC is too much). If the supply wires read 21 V AC with the board disconnected but 13 V with it connected, the board is pulling the supply down and has a short. 12–13 V will not power the board or the PIs. Verify with CE support.
• A board set for low-voltage signals fed with 149 V AC burns the plug-in resistors (see the conversion question above).

A driver does not control brightness, so replacing it will not cure dim displays.

1. Brand-new PIs that are very dim everywhere: check the label on the back of the PI. An MH222-BB… has blue characters, an MH222-RR… has red. Blue characters behind a red lens (or red behind blue) are barely visible. Match the lens color to the character color.
2. Individual segments dim on 10–15-year-old PIs: the PI boards are aging. Order replacement PI boards (for example, the plug-and-play replacement MSV11-WWX, identified from the serial-number label of the existing PIs); keep the existing driver.