While the David Marks repair is undoubtedly a good solution, at £3000, it’s nearly 10% of the value of the most recent Virage to sell on eBay (£35k as of 10/6/19). And a bit too much for us at the moment, for something that adds only a little to the enjoyment of the car.
So G. decided to have another look. After removing the unit from the car (new, easier method outlined in the ‘how to’ section), he looked at which of the components, such as the voltage regulator, capacitors, and ICs could be replaced. We had long thought that the problem might be a failed battery backup to the memory that stored the odo data, but there is no battery visible on the main board.
Looking hard at the circuit board, G. spotted a chip marked as the Dallas DS1287 RTC. Doing a bit of research, he found this was a pretty infamous chip, that causes problems on a lot of equipment from this era. Almost all computer systems rely on an RTC, or real time clock to provide basic system timing. RTC ICs ensure that all processes occurring in the system are appropriately synchronized and that’s why systems that use them cannot work if the RTC fails.
The Dallas DS1287 was a very common RTC chip at the time of the VIC design (1988-9?) to do this. The unit contains a crystal oscillator, a lithium battery, and a 50 byte memory to store the time data.
The fatal flaw in this RTC is that the lithium battery is not rechargeable (by design apparently for RTCs), and it is embedded in the epoxy casing of the chip, so cannot be replaced, or even seen. The Dallas DS1287 was used in many computers of the day, including the IBM XT, and many Compaq systems. When the battery dies, the PC cannot be started. G. thought this was likely a similar problem for the VIC. The chip is soldered on the VIC main board, and then more or less inaccessible behind the dashboard, so this was a really poor design for a chip that would have to die at some point.
While the Dallas DS1287 is no longer made, they are available on eBay, so we ordered a couple (£10 each incl postage from the UK, or a few pounds if shipping from China). G. also obtained a matching 24-pin socket, so that the RTC would not have to be re-soldered on to the board every time it was changed. As an alternative to replacing the RTC chip, a technique exists to connect an external lithium-ion battery to the RTC, and power it up anew. Garry first tried the latter method, so that the Li-ion battery could be more easily replaced. This turned out to work perfectly, and in fact is the method we would recommend, for reasons I’ll explain below.
Once the RTC had been modified, Garry installed the VIC back in the Virage. Caramba!! The VIC powered up immediately, and once the time and date information was entered, it all worked perfectly!! With one exception – the odo was still reading far too high. By repeatedly powering the backup battery off and on (via a switch on the battery holder), the odo dropped a little every time, until it reached a level that was pretty close to the actual true mileage. Note, you could not use this reset method if you had just replaced the old RTC with a new one. This is the reason we recommend modifying the old RTC as opposed to replacing it with a new one.
And all the functions work, starting with the odo.
and date, time and temperature!
It has to be said that the miles to km conversion is still out of whack, but with Brexit coming up, we won’t need km any more, so no problem there.
So a more or less fully working VIC, with a reset odo, for a total parts cost of £5.00!! It’s clear that the RTC enables the rest of the system, but other than time function, doesn’t do much else. Time and date info is now retained in the VIC even after removal for an hour or more, so the memory backup is restored.
It should be noted that the problem was not a failed rechargeable battery supporting RAM or EEPROM memory, as some have surmised. We still cannot find a rechargeable battery on the VIC – only the RTC has any li-ion battery power as far as we can see, and that is not rechargeable by design.
To get the full lowdown on how to do this repair yourself, click here.