Hp 8568B SA A15 Controller error - Page 1
Forum section: electronics / testgear

author: Simon Spiers
author_rank: Regular Contributor
timestamp: August 14, 2018, 08:54:33 pm
content: ~I have bought a non working hp8568b SA on a government auction site this week. On opening it up ?I see someone has had the 10Mhz OCXO out of it but other than that it is complete.However on power up I get no control from the keypad other than the instrument preset will respond. Looking at the A15 controller board, I see one of the I/O led's (the 4th in from the edge of the board it permanently lit.Has anyone got any info on this later controller (its not the same as the earlier A model) or maybe a schematic of fault finding chart. At the moment I have no idea what this led means and any feelers would be most appreciated.

author: KE5FX
author_rank: Super Contributor
timestamp: August 14, 2018, 09:09:58 pm
content: The manuals are extremely comprehensive on these, easily the size of several metro-area telephone books. That'd be your first stop in the quest for troubleshooting information. While some people prefer one or the other, I like to keep both the .PDFs and hardcopies close at hand.It may not boot without the OCXO, not 100% sure about that. Chances are the manual will say so, if this is the case. In any event it's unlikely that someone parted out a perfectly-working 8568B, so replacing the OCXO will probably not be the end of the troubleshooting journey on this one.

author: Simon Spiers
author_rank: Regular Contributor
timestamp: August 15, 2018, 07:32:02 pm
content: Thanks for your rely. ?It looks like there is no problem booting without the Ref Osc installed as there is only power and Oven status which is logic hi or low.I have found a manual and it is surgesting that either two Pal's ? are faulty or the eproms have lost their data.I ~have an eprom reader here but what type of eprom do i select to read? The list has no HP part numbers at all!The reader is a Gallep-5!Help please!

author: KE5FX
author_rank: Super Contributor
timestamp: August 15, 2018, 10:31:40 pm
content: Quote from: Simon Spiers on August 15, 2018, 07:32:02 pmThey are 27256s. I uploaded the images tohttp://www.ko4bb.comseveral years ago. Note that my readme.txt file says that 27C256 EPROMs will not work, but that turned out to be a mistaken impression on my part -- it was actually the EPROM burner I owned at the time that didn't work properly with 27C256s, not the 8568B.The PALs are very unlikely to be the problem.

author: G0HZU
author_rank: Super Contributor
timestamp: August 15, 2018, 11:43:30 pm
content: Nice find! If you start taking it apart, be aware that the various PCB edge connector pads are coated in a microscopically thin layer of gold to improve the contact performance. So don't use anything abrasive on these to clean them or the plating finish will be trashed even though it might still look the same to the naked eye. The manual gives instructions how to clean them.

author: Simon Spiers
author_rank: Regular Contributor
timestamp: August 16, 2018, 10:05:04 am
content: Hi KE5FX thanks for that. I have downloaded the eprom files and will do a comparison. The LED that is lit is pointing to an IO or data line stuck.I was wondering if the HPIB bus has got zapped and is causing the problem. Do you think it's worth trying to remove the GPIB controller IC to see if it clears the fault?This thing is a pain to get too as it uses 3 headers, one of a finer pitch than the usual ones found in gear of this vintage.Failing that I will try the shotgun approach and change what i can get hold of.

author: KE5FX
author_rank: Super Contributor
timestamp: August 16, 2018, 08:06:35 pm
content: Quote from: Simon Spiers on August 16, 2018, 10:05:04 amNothing's impossible, of course, but it's unlikely to be the GPIB controller unless you have some specific reason to suspect it. There are usually other ways besides the shotgun approach to track down a fault-indication LED.Unless the firmware version happens to match the files on ko4bb.com, the comparison will obviously fail. What I would do is simply erase the existing EPROMs and reprogram them with the latest available images. All this of course assumes that the manuals don't give you any solid troubleshooting leads.

author: Simon Spiers
author_rank: Regular Contributor
timestamp: August 25, 2018, 12:00:10 pm
content: Ok the latest is I have replaced the A15 Processor board as the fault diagnostics points towards a Data line being stuck or a ROM error.The ROM's have been checked are all correct, but still the same led (4) is on. I have confirmed the keyboard has no stuck keys so now i'm wondering if I have bought another duff board or the fault might be on the A12 Interface board that seems to handle data from the front panel. I have removed every board in succession and still that stupid led is on!As i am close to hopeless with computer stuff could anyone make any suggestions please?