TGA12101 error #127 system ram error, battery fault or firmware updated - RAM? - Page 1
Forum section: electronics / repair

author: petemate
author_rank: Regular Contributor
timestamp: February 07, 2021, 04:25:17 pm
content: I won this ebay auction for a "broken" TTI TGA12101 arbitrary waveform generator. The description and the photos of the unit indicated a good chance of repair. But it seems to be more trouble than anticipated. So all those who bid against me and lost, count yourself luckyQuestions are highlighed with bold text:Anyway, I receive the unit and it appears to be stuck in some kind of boot mode, asking me to select number of channels. There are three models in the range, with one, two and four channels. I press "1" and nothing happens. I look inside the unit and see that someone has been messing around with the RAM, the "flashless" MCU and the SPD(its kinda like a flash memory). It looks as though they have either been replaced or reworked. Lots of flux left. I clean up everything and try again. This time i am able to press buttons 1,2 or 4 to move on from the initial "select number of channels". The device boots, shows information about software version, gives a warning about not being calibrated and then gives error #127 "system ram error, battery fault or firmware updated". The display changes to indicate that one of the soft keys is "FCN" but the unit doesnt respond when i press that(or any other button).First I check the battery and everything looks good(CR2032 goes to ram, voltage level is fine), so I doubt that there is an issue here. Yes, software could be updated, but what about it? The "system ram error" is more likely and probably explains why someone reworked the RAM. The service manual of the unit indicates that the two RAM ICs are 256k x 16 bit. But the RAM ICs in the unit are 512k x 16 bit. I look up the datasheet for those RAM ICs and the pinout matches the pinout used in the schematic, but since the service manual only mentiones "256X16RAM 70NS 3V", I can't verify directly against the original IC datasheet. Speed and voltage ratings also match. I can see lots of activity on the address bus and on the data bus.Is different "sizes" of RAM interchangeable in that way? Can i just knock in a 512k IC if I don't have the 256k version, provided everything else is the same?The PSD(programmable system device) is what stores everything. It is also connected to the bus. The service manual calls for at PSD4135G2V, but a PSD4235G2V is mounted. I don't know if it got replaced or if ithey used this new IC during manufacturing. Pinouts are identical, so its could be that the old part was obsolete and they just switched to the new part(which is now also obsolete). In any case, since this unit correctly shows display messages and so on, it is likely that the software is also intact(and programmed from the factory, unless someone who replaced the IC was also able to program it).It has a JTAG port and I managed to get the programming software from the vendor. I just need to manufacture a simple JTAG cable and I should be able to re-flash the unit. if the manufacturer can/will send me the firmware.But is it likely that some of the firmware is corrupted, while something else is OK? Would the unit be able to start at all, if corrupted memory was the cause of the lockup?Now, attached to the MCU is also an FPGA. It is responsible for waveform point generation and controls the DAC. It also has its own "waveform RAM". The user manual mentions that "At power up the generator displays the installed software revision whilst loading its waveform RAM; if an error is encountered the messagesystem ram error, battery fault or firmware updated[ will be displayed."I then look at the waveform RAM and see something strange: It receives a clean clock from the FPGA, but there is no communication on the bus. Its as if the FPGA never initiates anything with the RAM. The write enable, which is active low, even remains high. Something is preventing the FPGA from using the RAM, whether intentional or otherwise. Thats where I'm stuck now.I have contacted TTI and asked for a firmware file and if they have any pointers, if they still even support the unit..