mc68000 based computer repair - Page 1
Forum section: electronics / repair

author: ddavidebor
author_rank: Super Contributor
timestamp: October 20, 2013, 08:26:28 pm
content: hi guys.i'm trying to throubleshoot and maybe repai the computer of an hp54502a oscilloscope.it's based on 68k microprocessor of motorola.at start up, it sometimes don't show anything on data or address.the reset is ok and the clock also is ok.sometimes, especially if i probe it, it start and data and address bus seems live.it's from 1992. apart from the ROM, what can be the failure based on your experience?

author: Rerouter
author_rank: Super Contributor
timestamp: October 21, 2013, 02:15:26 am
content: for a hp unit of that era its likely to mention a signature test mode in the manual, now decoding them wont get you far, but if one pin has a listed signature and you see a stable voltage on the pin you can narrow down your issue,

author: kb3pxr
author_rank: Contributor
timestamp: October 21, 2013, 02:35:11 am
content: If you aren't getting anything on the address or data lines you aren't even getting to the point of reading the ROM. How is that processor mounted? Is it an SMD or the older DIP package?

author: pickle9000
author_rank: Super Contributor
timestamp: October 21, 2013, 03:16:51 am
content: You can find the service manual here (no scematics but some voltages and flow charts)http://www.ko4bb.com/manuals/index.php?dir=HP_AgilentDouble check the power supply and the power good signal in particular, make sure it's not sitting in an ugly place. Is the processor getting hot at all? Check the processor clock on the chip (just too be sure it's good there).

author: ddavidebor
author_rank: Super Contributor
timestamp: October 21, 2013, 05:17:33 am
content: Quote from: Rerouter on October 21, 2013, 02:15:26 amCan you explain? I can't understand.Thankyou

author: ddavidebor
author_rank: Super Contributor
timestamp: October 21, 2013, 05:17:52 am
content: Quote from: kb3pxr on October 21, 2013, 02:35:11 amIt's a big dip soldered

author: ddavidebor
author_rank: Super Contributor
timestamp: October 21, 2013, 05:18:39 am
content: Quote from: pickle9000 on October 21, 2013, 03:16:51 amYes the clock it's good and the processor become hot, sometimes more than other.

author: Rerouter
author_rank: Super Contributor
timestamp: October 21, 2013, 06:20:05 am
content: HP around that time frame sold signature Analyzers as diagnostic gear for there equipment, essentially it generated a 4 digit hex code in reference to what ever signal it was looking at, with 0000 being static 0, and FFFF being static 1,for a piece of test gear i have, a DATA 6000 scope, which is built to use one of these analyzers, it has a test mode that essentially makes it loop in a pattern so these signatures can be generated,as for no data or address lines changing, note the state of every pin while working, then apply some freze spray until it plays up and measure again, its either going to be a dead chip or a bad connection

author: ddavidebor
author_rank: Super Contributor
timestamp: October 21, 2013, 08:08:55 am
content: that's a good idea since the board has some reworking it can be damageddo you know how can i probe and decode those signals?