1998 Honda Accord EX clock backlight?
#11
28 volts, say what?
So clock backlight blew out as well and I went to radio shack to get an LED to replace it. I tried a lower voltage one as well as some of the higher ones they had. After blowing both of those I remembered I had a volt meter and hooked that up and then realized that I had been trying to hook up 3 and 4 volt LED's up to something that had a 28 volt connection according to my volt meter. Then I found this thread and saw that people found the right LED at the dealer.
One can get LED replacement lamps that have a built-in current limiting resistor or regulator IC. Such LED lamps do have a voltage rating. The ones with an integral regulator typically have a very wide operating voltage range, perhaps 3 V to 18 V, but dimming control is next-to-nonexistent.
The bulb in the Honda Accord clock module is fed through two silicon diodes, one of which is connected to the +12 V ignition rail and the other to the instrument light rail for low intensity dimmable operation at night. The bulb, therefore, needs at least a 12 V rating, or 13-14 V rating for improved service life. (I measured 13.1 volts across the bulb with the engine running and the headlights off. With headlights on, the dimmer control varies the bulb voltage over the range of 3.8 to 11.1 volts.) Since the bulb is always on when the ignition is on, it will have a shortened life, so you might consider buying several spares when you visit the dealer. I just paid US$3.57 for one in California, including 9.25% sales tax.
The bayonet bulb receptacle in the clock module is designed for an incandescent bulb and is not polarized. If you should put a polarized LED replacement in there without making sure it can operate with either supply polarity, the LED is likely to get destroyed. LEDs will typically survive reverse polarity on a 5 volt supply, but not 12-15 volts, as the junction breakdown voltage is around 6 to 7 volts, depending on the specs.
The LCD display module is what's called an "edge-lit display" in avionics circles, meaning it has a slab of acrylic plastic under it and one or more small bulbs poke into the middle of the plastic through holes or cutouts to flood the layer with light. Incandescent bulbs are ideal due to their omindirectional radiation characteristics. If you want to use an LED, you'll need to choose carefully or customize, as most LED packages are designed to focus the light output into a narrow beam, which is lousy for illuminating edge-lit displays.
Due to the output characteristics of LEDs, they can't be dimmed very well on dimmer circuits designed for incandescent bulbs. If long lamp life is more important to you than smooth dimming, then an LED is a suitable choice as a replacement.
Last edited by phil8192; 08-11-2010 at 10:37 PM. Reason: add'l thoughts on lamp polarity, bulb characteristics, etc.
#12
Hi RTexasF,
Thanks for your response. I took the clock off the dash and opened it and there is a very small bulb (like the size of a LED) but I don't know how to remove the old bulb and replace it with a new one. Is this something that must be done at a Honda dealer? I hope not because I know they will kill you with the price of parts and labor. Speaking of light bulbs, is it possible to get a colored light bulb for the clock? I would love to have the blue colored illumination on my clock (just like those blue indiglo illumination on Timex watches) and dashboard to be blue just like the 86-97 accords... are those possible to do?
If you know the procedure to replace the light bulb, could you please help me? Thanks...
Thanks for your response. I took the clock off the dash and opened it and there is a very small bulb (like the size of a LED) but I don't know how to remove the old bulb and replace it with a new one. Is this something that must be done at a Honda dealer? I hope not because I know they will kill you with the price of parts and labor. Speaking of light bulbs, is it possible to get a colored light bulb for the clock? I would love to have the blue colored illumination on my clock (just like those blue indiglo illumination on Timex watches) and dashboard to be blue just like the 86-97 accords... are those possible to do?
If you know the procedure to replace the light bulb, could you please help me? Thanks...
The stock bulb in the clock should have a black or gray plastic base and a blue plastic silicone skin on it to give a bluish backlight to the clock. The hazard warning switch, mounted next to the clock in the same bezel, has a green base and no filter skin. The blue skin on the clock bulb may be partly responsible for its short service life, as well as a 12-volt rating, where it should be rated at 13 volts to 14 volts, the actual bus voltage when the car's alternator is operating normally. If you're in possession of the original bulb, the silicone skin may be (gently!) peeled off and transfered to the replacement bulb.
To see how to get the clock/hazard switch bezel out of the dashboard, see the AUTOTOYS.COM site at http://www.autotoys.com/New_Tech/DIY...ord/accord.htm. The page deals with radio installation and removal, but the photos also show the clock module removal. The bent tip end of a machinist's scribe is useful for getting the bezel started, or if you have a mechanic's pick set for removing o-ring seals, such as those sold by Snap-On Tools, it will work too. The fit of the bezel is so snug in the panel that it may be difficult to get anything thicker than a thin knife blade under its edge to gain a purchase on it. It is held in place with two b a r b e d plastic tabs at the top and two spring metal clips on the bottom. (Sorry about spacing the word starting with "b" in previous sentence; stupid filter in this forum keeps mangling what I'm trying to type, replacing it with asterisks. Do you hear that, Mr. Moderator?) Pry at the bottom of the bezel, not at the top, as the metal clips yield easily, while the plastic tabs at the top may simply break off! Get one side started, then the other. Once the gap has widened enough to get a small screwdriver in, use a flat blade screwdriver to coax the assembly out, or grasp it firmly on opposite sides with two fingers and pull it out of the panel. The clock module and the hazard warning switch are connected to the wiring harness with typical automotive plugs with retainer tabs that must be depressed to remove them. However, it should be possible to replace the clock bulb without unplugging the assembly.
Last edited by phil8192; 08-11-2010 at 10:42 PM. Reason: further information on nature of blue bulb filter
#13
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Phil1812 wrote on 8/11/10
snip..snip
The bulb in the Honda Accord clock module is fed through two silicon diodes, one of which is connected to the +12 V ignition rail and the other to the instrument light rail for low intensity dimmable operation at night. The bulb, therefore, needs at least a 12 V rating, or 13-14 V rating for improved service life. (I measured 13.1 volts across the bulb with the engine running and the headlights off. With headlights on, the dimmer control varies the bulb voltage over the range of 3.8 to 11.1 volts.) Since the bulb is always on when the ignition is on, it will have a shortened life, so you might consider buying several spares when you visit the dealer. I just paid US$3.57 for one in California, including 9.25% sales tax
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Good morning everyone. I'd like to continue this discussion, if that's OK. I bought my 17 year old a 99 Accord LX. I noticed the clock backlight wasn't working, so I replaced the bulb. Got that done with no problem. However, it's not acting quite right. When you turn the ignition on, the clock backlight is on and everything is hunky dory. However, when you turn the headlights on, the clock backlight goes out. So, it's like the bulb is burned out again. But, obviously, it isn't. Turn the headlights off, and the backlight turns back on.
Phil1812, after reading what you wrote about the two different sources for the backlight voltage, I want to make sure I understand you. Are there 2 sources for the backlight voltage (ie - 2 input wires on the clock connector)? Or, does the dimmer module take over for the fixed 12V when the ignition switch is turned on (ie - 1 input wire). The dimmer control works fine on everything else, so it's not that circuit. I'm wondering if there is a problem with the harness that brings the dimmer control voltage over to the clock (I REALLY hope that's not the case)? Or, is it possible that the clock module is bad? Does anyone have any kind of diagram showing the pinouts on the clock module connector so I know where to probe to look for fixed/varying voltage, or a board layout so I know what pad or trace to monitor for that voltage? If it's the module, is this problem something that can be user-repaired? I'm a EE, with soldering skills, so I should be able to fix just about anything, if I know how to find the problem.
One last question. Should the emergency flasher switch be lit when the headlights are on? This one isn't, at all. Is this a burned out bulb too? Haven't seen anything on any forums about that. But, haven't looked very hard either.
Any help would be appreciated. Thanks for listening!
Phil1812 wrote on 8/11/10
snip..snip
The bulb in the Honda Accord clock module is fed through two silicon diodes, one of which is connected to the +12 V ignition rail and the other to the instrument light rail for low intensity dimmable operation at night. The bulb, therefore, needs at least a 12 V rating, or 13-14 V rating for improved service life. (I measured 13.1 volts across the bulb with the engine running and the headlights off. With headlights on, the dimmer control varies the bulb voltage over the range of 3.8 to 11.1 volts.) Since the bulb is always on when the ignition is on, it will have a shortened life, so you might consider buying several spares when you visit the dealer. I just paid US$3.57 for one in California, including 9.25% sales tax
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
Good morning everyone. I'd like to continue this discussion, if that's OK. I bought my 17 year old a 99 Accord LX. I noticed the clock backlight wasn't working, so I replaced the bulb. Got that done with no problem. However, it's not acting quite right. When you turn the ignition on, the clock backlight is on and everything is hunky dory. However, when you turn the headlights on, the clock backlight goes out. So, it's like the bulb is burned out again. But, obviously, it isn't. Turn the headlights off, and the backlight turns back on.
Phil1812, after reading what you wrote about the two different sources for the backlight voltage, I want to make sure I understand you. Are there 2 sources for the backlight voltage (ie - 2 input wires on the clock connector)? Or, does the dimmer module take over for the fixed 12V when the ignition switch is turned on (ie - 1 input wire). The dimmer control works fine on everything else, so it's not that circuit. I'm wondering if there is a problem with the harness that brings the dimmer control voltage over to the clock (I REALLY hope that's not the case)? Or, is it possible that the clock module is bad? Does anyone have any kind of diagram showing the pinouts on the clock module connector so I know where to probe to look for fixed/varying voltage, or a board layout so I know what pad or trace to monitor for that voltage? If it's the module, is this problem something that can be user-repaired? I'm a EE, with soldering skills, so I should be able to fix just about anything, if I know how to find the problem.
One last question. Should the emergency flasher switch be lit when the headlights are on? This one isn't, at all. Is this a burned out bulb too? Haven't seen anything on any forums about that. But, haven't looked very hard either.
Any help would be appreciated. Thanks for listening!
#14
Yep, two separate feeds for the backlight
Phil1812, after reading what you wrote about the two different sources for the backlight voltage, I want to make sure I understand you. Are there 2 sources for the backlight voltage (ie - 2 input wires on the clock connector)? Or, does the dimmer module take over for the fixed 12V when the ignition switch is turned on (ie - 1 input wire).
The clock backlight is rather dim when running with the headlights on, and may not be visible in daylight, unless you tent it with something dark, similar to the focusing hood used by photographers working with old style view cameras. Do that before undertaking major disassembly.
#15
Yes, there are two separate circuits feeding the clock backlight. That's the reason for the two diodes on the clock circuit board. When the headlights are switched on, the battery rail voltage is removed from the clock module backlight; if it weren't, the higher voltage through the two diodes would always override the lower dimmer voltage and the dimmer would have no effect. If your instrument panel is lit and responds to the dimmer control when the headlights are on, but the clock doesn't, I'd check to see if the clock is OK or the wiring is feeding the variable voltage from the rheostat to the clock. There's a plastic cover on the back of the clock circuit board that one can (carefully) remove to make probing the diodes easy. The hazard warning switch is connected with a separate connector coming off the wiring harness, so I don't know offhand if it is fed off the dimmer circuit like the clock.
The clock backlight is rather dim when running with the headlights on, and may not be visible in daylight, unless you tent it with something dark, similar to the focusing hood used by photographers working with old style view cameras. Do that before undertaking major disassembly.
The clock backlight is rather dim when running with the headlights on, and may not be visible in daylight, unless you tent it with something dark, similar to the focusing hood used by photographers working with old style view cameras. Do that before undertaking major disassembly.
Thanks for getting back to me. I appreciate your taking the time. It's saved me a good bit of research time. If you have any more answers to my questions, I'd appreciate hearing back from you again.
Talk to you later.
#16
The wire colors are off a 98-02 shop manual that covers European accords, so the colors may not be identical.
At the clock wire harness there should be 4 wires: Blk, red/blk, yel, and pnk.
Blk is ground, so check for continuity to ground (a something bolted into metal will work).
PNK should always have voltage (for clock memory)
YEL will have voltage when the key is in the I or II position.
RED/BLK will have voltage when the headlights are turned on.
From the wiring diagram, it looks like voltage will be 12V, as they are in line with the fuses. I could definitely be wrong on the voltage.
At the clock wire harness there should be 4 wires: Blk, red/blk, yel, and pnk.
Blk is ground, so check for continuity to ground (a something bolted into metal will work).
PNK should always have voltage (for clock memory)
YEL will have voltage when the key is in the I or II position.
RED/BLK will have voltage when the headlights are turned on.
From the wiring diagram, it looks like voltage will be 12V, as they are in line with the fuses. I could definitely be wrong on the voltage.
#17
The wire colors are off a 98-02 shop manual that covers European accords, so the colors may not be identical.
At the clock wire harness there should be 4 wires: Blk, red/blk, yel, and pnk.
Blk is ground, so check for continuity to ground (a something bolted into metal will work).
PNK should always have voltage (for clock memory)
YEL will have voltage when the key is in the I or II position.
RED/BLK will have voltage when the headlights are turned on.
From the wiring diagram, it looks like voltage will be 12V, as they are in line with the fuses. I could definitely be wrong on the voltage.
At the clock wire harness there should be 4 wires: Blk, red/blk, yel, and pnk.
Blk is ground, so check for continuity to ground (a something bolted into metal will work).
PNK should always have voltage (for clock memory)
YEL will have voltage when the key is in the I or II position.
RED/BLK will have voltage when the headlights are turned on.
From the wiring diagram, it looks like voltage will be 12V, as they are in line with the fuses. I could definitely be wrong on the voltage.
Again, I really appreciate your time and help.
#18
The wire colors are off a 98-02 shop manual that covers European accords, so the colors may not be identical.
At the clock wire harness there should be 4 wires: Blk, red/blk, yel, and pnk.
Blk is ground, so check for continuity to ground (a something bolted into metal will work).
PNK should always have voltage (for clock memory)
YEL will have voltage when the key is in the I or II position.
RED/BLK will have voltage when the headlights are turned on.
From the wiring diagram, it looks like voltage will be 12V, as they are in line with the fuses. I could definitely be wrong on the voltage.
At the clock wire harness there should be 4 wires: Blk, red/blk, yel, and pnk.
Blk is ground, so check for continuity to ground (a something bolted into metal will work).
PNK should always have voltage (for clock memory)
YEL will have voltage when the key is in the I or II position.
RED/BLK will have voltage when the headlights are turned on.
From the wiring diagram, it looks like voltage will be 12V, as they are in line with the fuses. I could definitely be wrong on the voltage.
Also, the emergency flasher switch/module has the same low voltage bulb the clock has in it and that's blown too. So, a new bulb in that will fix it so the flasher switch can be seen.
Just wanted to say thanks again.
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