Tektronix 468 - displays all traces - Page 1
Forum section: electronics / testgear

author: Analogdevice
author_rank: Contributor
timestamp: May 25, 2015, 09:19:33 pm
content: Hello friends,I gotta problem with my tek 468. After power up, the display on storage display board shows number "1000", light on CH1 and 2 switches (probe coding) lights permanently (x1, x10) and on CRT are displayed all traces, incl. trigger, CH1, CH2 etc.I think that there is problem with logic, because storage mode can´t be turned ON, equally the cursors are dysfunctional.Please, can you give me an advice, where is problem?Thank you very much.

author: tautech
author_rank: Super Contributor
timestamp: May 26, 2015, 02:34:22 am
content: Maybe you should have started this thread in the "Repair" board where you will find the Tek troubleshooting guide and links to sevice manuals.However, the first step is always to check the PSU is exactly to spec and I'm guessing you'll find the logic powered from the 5V, so that must be to spec too.

author: Analogdevice
author_rank: Contributor
timestamp: May 26, 2015, 10:15:22 am
content: PSU is OKAY, I checked this first, because there was problem too with some tantals. Now all voltages are in tolerance with service manual table.I checked vertical mode switch board. There is IC U458, but clock input are still HI. Is that OK?And sorry, I´m relatively new here

author: MarkL
author_rank: Unknown
timestamp: May 26, 2015, 06:43:04 pm
content: What *does* work?Do you have another scope to troubleshoot this?

author: Analogdevice
author_rank: Contributor
timestamp: June 07, 2015, 10:18:51 pm
content: Horizontal channel and trigger generator.I think that problem is in digital part + maybe in vertical mode switch. Power supply is OK, HV supply is OK, intensity is OK but when I connect flat cable from back PCB, where is CPU, the trace blinkong and intensity of trace is at mid.And yeas I have another scope to troubleshoot this one.

author: iDevice
author_rank: Regular Contributor
timestamp: June 08, 2015, 06:25:51 pm
content: The scope won't do anything as long as you are stuck in self-test mode.I don't remember by heart what means the 1000 error code but you just have to check the service manual.Each digit represents a series of test results (0 to 3 if I remember correctly) for 4 functional groups. (like system RAM, Acquisition RAM, Display RAM, etc)Once the boot self test is complete (display flashing each digit during the test sequence and then going dark) the CPU initializes the I/O's and all indicators light-up correctly, indicating the real status and vertical switching modes become operational.The 468 is basically a 465b but most knobs are not acting directly anymore and are read by the CPU which then in turn is driving the circuits, so even in analog mode, if the CPU is not running, the scope is dead.The most usual failure on these scopes is the Mostek ROM's rot.But in your case you get to the point where you get an error code so you are beyond the ROM checksum part of the self-test because if the checksum fails, the CPU halts and the display remains dark.If you don't have the service manual I can check the error code for you but I strongly suggest you download a copy if you want to fix this scope.

author: iDevice
author_rank: Regular Contributor
timestamp: June 08, 2015, 08:32:10 pm
content: Ok, I just checked in my service manual and 1000 means a March test error in the acquisition RAM.I would suggest to set the Service dip switch 7 in open position to bypass RAM tests and see if you get further.With a bit of luck, the power-on self test will terminate and you should be able to get control of the front panel.Scope should be usable in analog mode but because there is a problem in the acquisition RAM, in digital mode you should get cursors and a trace but bad waveform or parasitic waveform.