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by Jeremy Schrag
Recently, we featured an article that took us on a fascinating journey through the history of Huntsville Electronics, the Chrysler division responsible for most of the company’s electronic products for decades. And though I have personally showed you the insides of many of the division’s audio products, there is more to Huntsville than a few car audio head units. Much more.
They were also responsible for most of Chrysler’s digital instrument clusters. Today, I’m looking at one of the more innovative and yet problematic versions of their clusters, found in the 1992-1993 AC/AY body vehicles (Imperial, New Yorker, and Fifth Avenue). A version of this is also found in the later AA body LeBaron.
Here is the cluster in proper working order, running in the dash of my 1992 Imperial (the New Yorker and Fifth Avenue are similar). This type of cluster is rather nice to look at, using sweep style gauges as it does.
Being nice to look at, in this case, is the downfall of this particular cluster. Earlier digital clusters used reliable vacuum florescent displays (VFDs). This one does not. Back in the early nineties, it wasn’t possible to make a cluster using VFDs that looked like this. It was just a limitation of the technology of the day. Huntsville changed their approach to get around this obstacle - they used Liquid Crystal Displays (LCDs) instead. They figured they could now design a digital cluster that was not only functional and reliable, it looked good as well.
They only succeeded on two of the three counts. The new cluster was functional, and it was good looking. But it was not reliable. See, for LCDs to be used, they must be backlit. In 1991, we didn’t have a strong technology for this purpose. Electroluminescent panels were short-lived in automotive environments, and light emitting diodes weren’t bright enough. What was Huntsville and Chrysler to do? Why, just use plain old light bulbs, of course.
But light bulbs carry their own sets of problems. After a while, they burn out. When they don’t burn out, they release heat. Lots of heat. As it turns out, LCDs don’t like being exposed to heat day in, day out, for years. More on that later.
For now, let’s look at this picture. This is the original cluster that came with my Imperial, and it is defective. Here, I’ve caught it in the middle of its power-up self test, using the factory backlight bulbs. Yes, that’s about as bright as these clusters get with their factory backlighting. Yes, it’s very hard to see in direct sunlight. Can you spot the problem with this cluster? I’ll give you a not so subtle hint - look at the temp gauge. See the missing segments? That’s what happens to this cluster, folks, when the heat becomes too much. I’ll give you some tips on how to service the cluster in a bit.
In the meantime, the cluster needs to come apart. You do not need to remove the Torx T-20 screws that hold the clear plastic face on (green arrows) unless you wish to clean between it and the black plastic bezel beneath. The red arrows indicate the T-20 screws that hold the entire front bezel to the assembly. Those are the ones we must remove; but before we do that, a look at the backside.
The shifter assembly is not present in this picture - it would normally fit into that big rectangular opening. Its indicator bulb goes into that round hole above the opening.
If you wish to remove the internal mainboard from the assembly, you will need to remove the arrowed metal mounting clip for the single red connector. You will note that there is an opening for a second connector on the left side of the picture - this is where the second connector for the LeBaron version of this cluster goes. Why does it need two connectors, while this one only has one?
Quite simply, it’s because this cluster gets all its information over the CCD bus from the body computer (BCM). Mileage, speed, fluid levels... it all comes out of the BCM on the AY body cars. The LeBaron has a self-contained cluster, which is otherwise similar; all sensors go to the digital cluster instead of the BCM, making the LeBaron version desirable for owners of other Chrysler vehicles that never got one of these clusters, and yet still enjoy the same opening in the dash. While, physically, this cluster will mount in many Mopar vehicles of the era, only the AA version can be made to work electrically — with a fair bit of rewiring.
Now that the front bezel is off, I’ve left this cluster powered to show you the light leakage around the LCD module from the bulbs behind. To access them, the LCD module must be unscrewed and ever so gently lifted out of the way.
Red arrows indicate the T-20 screws that hold the LCD assembly in place. Two of them are longer than the others - remember where they go. Green arrows indicate the #74 bulb locations that provide general illumination to the cluster. These are used for no more than giving the clear front panel a general green glow at night. They do little for this cluster in the grand scheme of things, and replacement of them is entirely optional. Many of you may have all four of these burned out, and yet have never known how they look in operation because they have always been burned out.
You can also see in the above picture more heat damage to the LCD segments in the speedometer window. The zero looks more like a seven. Why is there no odometer, you ask? It’s because on the AY body cars, as I mentioned, this information is stored in the BCM. There’s no BCM on the test bench to get this information from, and so there’s nothing to provide the cluster with any information. The odometer is therefore dark, the gauges have no needles, and the asterisk (normally used to indicate odometer rollover) is flashing.
The displays are supposed to look green, but because the green tint on this particular cluster isn’t really very green at all, they appear blue in this picture.
Before I lift the LCD assembly out of the way to show you how to access the illumination bulbs, I wanted to give you a close-up look at the damaged LCD panels so you can see what to look for on a potential replacement cluster at the yards. There are actually three LCD panels enclosed in one assembly - one for speedo and odometer, one for temp and volts, one for fuel level and oil pressure. You can replace any of these individually as needed.
This is how I identify a defective cluster at the salvage yard: I take the front bezel off the cluster, then hold it up to the light and look at each segment carefully. The volts section above is a gauge with no damage, and the temp section is one with extensive damage.
This is the speedo section of the cluster with the power off. Arrows again show the damaged areas, to give you some idea what to look for.
As long as you find a cluster with undamaged LCD panels, you can use them for parts. I’ll tell you how to replace the individual panels in a few moments.
First, this is a look at the underside of the LCD assembly, so you can see the illumination bulbs. You must gently hinge the assembly up and out of the way - there are six ribbon cables up top that must not be broken. There are six bulbs, two per LCD display, and according to my owner’s manual the part number for these bulbs is #7730. That said, I have not been able to find proper replacements for these. You can use #168s for alternates, but you will still have issues with heat and brightness. I prefer LEDs as replacements.
From here, you can already replace these bulbs. Just pull them straight up and out. Countless clusters like this are out there with one or more burned out bulbs. Most of these will have dim or completely dark LCD panels, perhaps leading their owners to wonder how fast they’re going.
Now, we’re going to look at the underside of the mainboard. Lift it upwards gently and hinge it toward the bottom of the cluster like so. You will see two ribbon cables near the bottom, which run to the two rows of indicator lamps on the very bottom of the cluster.
I’ve arrowed these cables in blue, to match the blue friction fit connectors they’re attached to. Just grab the blue connectors and pull them off - you can now remove the mainboard.
Note the six ribbon cables up top - these are, again, for the LCD panels.
Before we get too far with the mainboard, here’s a close look at some of the idiot light bulbs. These are PC194 type that twist into the assembly.
One of the working components of the cluster is this transistor, a Harris model I cannot find data for, as it uses a proprietary Chrysler part number.
The cluster uses two of these Hitachi HD61100SJA LCD drivers to control all three LCD panels. Here, we can also see that the illumination bulbs for the LCD panels are actually mounted in twist-lock bases.
Here’s one of the bulbs in its base removed from the cluster. You should never have to go this far to service the LCD illumination, but I’m showing it to you just in case you break a base and need to find a replacement.
The few remaining chips that operate this cluster include a Harris at the bottom of this picture that interfaces with the CCD bus. Re-solder the joints under this chip if your cluster periodically loses all the gauges on the highway, and gives you the flashing asterisk. It is likely that the AA version of this cluster is entirely different in this regard, but not having even seen one of those I cannot say how different at this time.
This ST Microelectronics voltage regulator is found near the left side of the cluster. It also uses a proprietary part number.
Now, more on replacing the LCD panels. Pull the affected panel’s ribbon cables out of their connectors on the back of the mainboard. They are a tight friction fit.
If you haven’t already done so, unclip and remove the big black metal plate on top of the display assembly.
Now, you can gently lift up and remove the offending LCD panel. I recommend gloves during this procedure, to prevent getting skin oils on the LCD panels. I’m not using gloves in the photo, because this panel is one of the defective ones.
Put the new panel back in the same way the old one came out. Double check that the ribbon cables are routed correctly, then re-install the black metal top plate.
Below the panel I’m working on here, you can see three button switches with missing plungers and contacts. Very often, these will need to be cleaned or replaced.
Here’s another cluster with intact button switches. They are the same parts found on most Chrysler digital clusters, as well as most of the older Quartz Lock radios. Parts are all interchangeable.
To get at the contacts, pull the plungers up and out like this.
Here’s the contact, located in the base of the plunger. You can see that the little center piece has buckled and broken, leading it to lack any springback action. Remarkably, this does not usually stop the switch from working, because it is the outer edge that provides the contact and you must press firmly for it to make contact, regardless of the spring action.
However, you will likely have to clean the contact, as well as the contacts down in the main body of the switch. After several years in a vehicle’s dashboard, these will usually end up dirty and unusable.
Now, we’re going to look at replacing those light bulbs under the LCD displays with cool running LEDs. Here are two of the various kinds you can get, both of which came from eBay and were very cheap.
These are standard #168 style LED replacements. One has a single ultra bright off-white LED, the other has five ultra bright pure white LEDs.
You might be sitting at home thinking to yourself, "Gee, that one on the right looks like just what I need. This cluster’s never been very bright. I’m going to get six of those, and rule the world." My response to that is... don’t do it. The one on the left is the one you want, and will be plenty bright enough. In fact, because you cannot dim these LED bulbs much (the dimmer circuit in these clusters is intended for old fashioned light bulbs), the five LED model is downright dangerous to use at night. They are ridiculously bright.
Let me plug these both in and show you the difference. You must plug these in with the cluster powered, so you can tell which way is the correct polarity. How do you do that? Well, you either have to use a bench power supply, as I am, or very carefully do it with the cluster still in the vehicle. I’ve gotten that down to a science now.
Not only is the five LED model absurdly bright, that LED on top will give you an extra bright spot in the display. Being mounted up higher, it comes too close to the LCD panels. And because it’s a pure white model, your red needle pointers will now take on a blue tint. The gauges themselves will also be blue, instead of the olive green you get with regular bulbs.
By contrast, the off white single LED model is closer to the correct color temperature for the displays, and is still bright enough to give you much better illumination in direct sunlight. Your gauges will still be blue, but the red pointers will be a purer red. See my first picture in this article to have a look at all six of these in action.
Let me just flip the LCD assembly down again so you can see the difference.
As you can see here, the five LED model is so bright all of the pointers are showing, even though there is no pointer currently active. You might be thinking you can live with that, but it gets worse. If you plug a five LED model into all six locations, they simply overwhelm the LCD displays. All segments will emit some light all the time the cluster is active. They are so bright at night, I had to drive with something covering up the cluster so I could see where I was going.
In fact, even the single LED off white model is too bright for me. I still can’t dim it far enough. If you find yourself in the same pickle, fear not. Just try another color that works better for you. You can use any color LED bulb you can get your hands on.
This is what six green ultra bright single LED bulbs look like in use. These are much more tolerable for me at night, though the needle pointers no longer look red. They’re more of an orange color.
And so I conclude my first look at a Chrysler digital cluster. I have two more of these on the shelf I’d like to write about in the coming months, including ones from a 1987 LeBaron GTS and a 1988 New Yorker. I look forward to showing you those.
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