Hi Guys,
While repairing TTI TG1040 RF generator, and I have found very strange fault. The instrument in general was dead, meaning screen was off only back light, but some times worked with some errors on LCD screen (not error codes simply some characters ware bad) the condition that never lasted for more than 5 min and then eventually all display fade out returning to "brick" state. I was able to regularly repeat condition but without any change. I noticed that instrument is actually working and that problem is display and keyboard. Based on those observations I was able to narrow down problem to control module with MC68HC11 MCU that works with external 32K flesh and 8K RAM. On first I thought that problem is with flash chip and SW (since the display had errors and behaviour was not stable) but unfortunately all was ok there. As last resort I have tried to re-solder board in order to avoid eventual soldering problems. Curiously enough I have found that there are no soldering problems, but Instrument works fine if I heat-up MC68HC11 with soldering iron. It seams that it has some internal problem which is resolved when heated. I will probably change the MCU and I expect instrument to return to working condition, buy while I am waiting for new chip to come I was wondering if someone had or at least heard for similar problem. I know that flash chips sometimes can be repaired with heat, but this particular MCU has no internal ROM/Flash...