Hi all,

Not sure if this is the right place but hoping someone can help.

I had a automotive LCD manufacturer produce some new LCD displays for an older vehicle (used to be manufactured between 1999 and 2005) as the original LCD displays had a design flaw in the way two ribbon cables were bonded, where delamination would occur causing lines to appear on the display.

Unfortunately there is no build data or designs available for the LCD displays, however the automotive LCD manufacturer was able to replicate the displays using the original ones, with a new improved soldered connection between the two ribbon cables. All works well however we have discovered that the LCD display dims when the instrument cluster's circuit board (to which the LCD display is mounted to) gets warm. We've traced the issue to a SRAM chip on the board for the LCD display (part number ZMD U62H64SA). This chip seems to be extremely sensitive to heat. It doesn't require much heat for it to get warm enough to cause the dimming problem with the display. For example, having the dash heater vents on hot for about 15 minutes generates enough heat behind the dashboard to cause the display to dim, or the interior of the vehicle getting hot on a hot day (when temperatures are around 25oc or more) causes it too. Even applying heat to this chip with a hair dryer set to the lowest heat setting quickly causes the problem to occur. The original factory LCD displays were also affected by this issue, however it required slightly more heat to cause the problem. It's not the display itself, as that has been tested by heating just the display to 60oc and it still operates absolutely fine. Apply even half that amount of heat to the SRAM chip and you'll see the display dim to the point it's unreadable.

The manufacturer has been unable to find any effective way to keep the SRAM chip cool, or understand why this is happening. The problem is the chip isn't getting particularly hot, but is so sensitive to heat that the normal ambient temperature is causing issues. The manufacturer has tried adding a heat sink and a cooling fan, but the issue is this just sucks the warm air around the instrument cluster in towards the SRAM chip so doesn't help at all.

The first pic attached shows how the LCD displays when the SRAM chip is at a cooler temperature. The second pic attached shows how the display looks when it dims, caused by applying heat directly to the SRAM chip. The third pic attached shows the SRAM chip on the board.

I don't have a electronics background, so finding a solution to this myself is well beyond my capabilities. I'm just a member of the enthusiasts club for this model vehicle and have been trying to find a effective replacement display made to solve the issue of failing factory displays. If anyone has any suggestions or potential solutions that would be really appreciated. We've been trying to solve this for around a year now.

Many thanks
Rick

 

Sounds like problem that will take extraordinary measures.

Perhaps a custom designed TEC cooler?

 

Welcome to AAC.

First thing I'd try myself is to run the display and have a can of cold spray to cool the chip and see if the problem comes and goes with chilling and warming the chip. It's possible that might not be the actual issue. Fully diagnose before you fix.

Generally heating the area doesn't isolate the exact location of the problem. A hair dryer will cast a lot of heat over a wide area of components. You COULD be chasing the wrong ghost(s).

 

The car is very old and it is time to replace it.

 

Not all of us can or think we should replace a car when the ashtrays get full.

I would take it to the dealer and ask whether or not they have a solution. Temperature compensating something like this would take a lot of time and a lot of temperature cycles, plus you would have to learn a lot along the way, and I doubt that learning how to temperature compensate a liquid crystal display circuit is one of your highest priorities. An assumption, mind you.

 

Many of the cars in Cuba are Name-Brand American and are about 68 years old. They guzzle a lot of gasoline but the island is small so the trips are short.

 

OK, here's my theory. Yes, the U6264AS1A is a "Automotive 8K x 8 SRAM" designed for wide temp range.
It is obviously wired to a device just off-screen to the top, that I will call Display Controller" or DC.
Next, I notice your display is a 5-6 line, 8x10, 15 char per line or roughly 50 x 120 = 6K pixels.
Your SRAM is 8Kx8, therefore I believe this SRAM is your display buffer with each pixel being an 8-bit intensity.
From your description you are not losing memory contents as when the part cools, the display intensity returns.
But, what if you were losing a bit on your data bus (i.e. was a 1 and goes to 0), then all pixels would uniformly decrease in value and the result would be lower overall intensity...
From your picture and the SRAM data sheet, the eight (8) PCB traces coming from under the left side of device are most likely the 8-bit data bus and they route up to the DC above and the signals pass thru black, 8-pin devices.
These 8-pin devices are most likely quad serial resistors (i.e. 4 per package) that are being used for serial termination to reduce signal degradation such as ringing and possibly edge speed for EMC reasons.
Serial termination resistors are typically 22 to 33 ohms AND they should be placed close to the "driver".
So, Item (1) - What is the number on those little black 8-pin parts as the jpeg is blurry and it looks like 102 which would be 1K and this would absolutely be a problem/design flaw.
Next, Item (2) - As mentioned serial term resistors should be placed close to driver, BUT a data bus has multiple drivers, the DC drives data when writing the buffer memory and the SRAM drives the data bus when the display buffer is read by the DC.
SO, Which driver gets the series term?? Answer (and this is always debated), no one. Series termination should not be used on a bi-directional data bus (once again, always debated).
So, my theory is that when you heat the SRAM part you are "weakening" its drivers and combined with the mis-used series termination resistors and the fact that the 8 data traces have different lengths are causing one of the data bits to be received incorrectly by the DC resulting in reduced values, hence reduced intensity.
The two (2) black, 8-pin devices on the left (out of five, the other three are used properly on address lines), could be removed and replace with shorting wires (i.e. 4 wires: 1-8, 2-7, 3-6, 4-5) as a test.

 

Rather then some screwy change in a memory chip, isn't it much more likely that the LCD contrast voltage needs to vary with temperature?

 

Rather then some screwy change in a memory chip, isn't it much more likely that the LCD contrast voltage needs to vary with temperature?

Not when TS states, rather definitively, that applying heat to the SRAM causes the display intensity to dim.

He said: " The first pic attached shows how the LCD displays when the SRAM chip is at a cooler temperature. The second pic attached shows how the display looks when it dims, caused by applying heat directly to the SRAM chip."

Also, the voltage you refer to would adjust contrast and from the picture it looks like he's losing intensity and that is dependent on the 8-bit pixel value.

 

Even applying heat to this chip with a hair dryer set to the lowest heat setting quickly causes the problem to occur.

He said: " The first pic attached shows how the LCD displays when the SRAM chip is at a cooler temperature. The second pic attached shows how the display looks when it dims, caused by applying heat directly to the SRAM chip."

》A hair dryer is not exactly a pinpoint source of heat, so the LCD will experience some amount of heating when the SRAM chip is being blasted.

》The original poster believes it to be the SRAM because pointing the hair dryer in its vicinity caused the problem. What if any steps were made to shield other components from the heat?

》The SRAM is rated to operate to at least 70°C depending on the version, and quite possibly to 85°C if it's an industrial/automotive grade part.

You can bet on the zebra or even the unicorn if you like; I'll stick with the horse.

 

I am relying on the clarity and quality of the information given.
Hopefully, the TS will follow through and we will discover the answer.
Oh, you might have missed this part of his post: "It's not the display itself, as that has been tested by heating just the display to 60oc and it still operates absolutely fine. "

That said on the lower left is an Elmos 10020B (voltage requlator) and some discrete components (i.e. caps). It is possible that this circuit is generating voltage(s) for the LCD and is the heat sensitive point. With the proper shielding the TS should be able to narrow down. Never mind as further search shows it as a "Link-Bus Transceiver" with internal voltage regulator (not a voltage regulator).

As mentioned, the best is a combo of heat and "freeze spray", where you heat until failure and then hit the suspect with freeze spray which is more pinpoint, looking for quick recovery.

The TS also states that manufacturer has been attempting to solve so one might think they know what they are doing (i.e. the horses have been ruled out).

 

I am soooo sorry my one sentence comment has triggered you so. Please erase it from your mind and forget I ever made it.

I suggested a common solution to a common problem which wasn't mentioned up until that point.

 

Not sure why you're apologizing I only pointed out the great lengths the TS had gone to and how confident he was that the problem originated with heat to SRAM. Just assumed you missed the details in reading his post. Of course, maybe he hasn't been as rigorous as I suspect.

 

First thing I'd try myself is to run the display and have a can of cold spray to cool the chip and see if the problem comes and goes with chilling and warming the chip. It's possible that might not be the actual issue. Fully diagnose before you fix.

Generally heating the area doesn't isolate the exact location of the problem. A hair dryer will cast a lot of heat over a wide area of components. You COULD be chasing the wrong ghost(s).

As mentioned, the best is a combo of heat and "freeze spray", where you heat until failure and then hit the suspect with freeze spray which is more pinpoint, looking for quick recovery.

But then again some people just don't read the entire comments before they offer their pearls of wisdom.

》A hair dryer is not exactly a pinpoint source of heat, (see above) so the LCD will experience some amount of heating when the SRAM chip is being blasted.
》The original poster believes it to be the SRAM because pointing the hair dryer in its vicinity caused the problem. (see above) What if any steps were made to shield other components from the heat?

I suspect the TS has not shielded anything on the board. That's why I said in post #3 a hair dryer is not a good way to check a single component for heat failure.

 

I've seen a great many posters here absolutely confident in their ideas that ultimately prove to be wrong. So pardon me if I don't accept every statement as a true fact.

In fact, much of my career has been solving problems by starting with "I have a dumb question, but somebody has to ask them. Have you checked the....." which has often been followed by a sheepish "No" and the problem is soon resolved.

But I won't bother you any further.

 

@Tonyr1084 don't be childish.

 

@Tonyr1084 don't be childish.

OK, I'm not going to escalate this. But that wasn't necessary. Seems you've been chiding everything I say on my thread with the dishwasher pump motor that I'm trying to understand how it works. You could be helpful. Or you could think I'm a moron. But you don't need to resort to name calling.

 

But then again some people just don't read the entire comments before they offer their pearls of wisdom.
I suspect the TS has not shielded anything on the board. That's why I said in post #3 a hair dryer is not a good way to check a single component for heat failure.

Don't worry you got your attribution, I said "As mentioned ...."
Sorry it doesn't read "As mentioned by Tonyr1084 in Post #3 Today at 10:53 AM"

 

you got your attribution, I said "As mentioned ...."

Yes, I knew that from the get-go. I quoted you because it was backup of what I had said earlier. It was for others benefits. You and I are on the same page.

 

One way of chilling a specific component is to take a Q-tip and freeze the tip, then touch it to the suspect chip. Given that this may be a larger chip you might try freezing three Q-tips and placing them directly on the surface of the chip. As for heating the chip - a soldering iron can bring a lot of thermal energy to a specific point. That way you're not heating everything on the board. Like I said before, you could be chasing ghosts. Put it another way you could be chasing the wrong failure point. It could be a transistor nearby. Or some other component. The point is to fully diagnose the problem and to KNOW what you need to fix. Otherwise you may end up with a new board for your LCD.