HP 8566B - Does not boot. Anyone have firmware or know the CPU board well? - Page 1
Forum section: electronics / repair

author: pnv57
author_rank: Contributor
timestamp: June 17, 2020, 01:15:26 am
content: I've just received a used 8566B and 80662A both listed as parts, but with good power supplies. The 8566B won't boot (error lights 1 and 2, which point to the uP board A15), and none of the 14 debugging LEDs light up on the CPU card (which the manual says should, and then blink out one by one). I followed the service manual steps to check the clocks on the 74HC112 dual negative edge JK flip-flops, both of which were fine. The manual then says to use heat and freezing spray to diagnose intermittent failures. I used my thermal camera, and the only warm chip was the PAL U20 (5180-2330). With my oscilloscope, I probed test pin bank No.1 (low, high, high, high, low, low, low, low, high) and then two ROMs and two SRAMs. Each one of them showed activity on the random pins I checked, and were repeating in a cycle that was 7 accesses long. With my limited knowledge, I think it appears that the CPU is stuck in a loop of some kind. Would the SRAMs, EPROMs, or the PAL be the most likely culprit? Or am I in the wrong place entirely? I have the "G" version ROM on the CPU board labelled 85660-60260 (which is a sticker over the original label of 85660-60182). Does anyone have any firmware (preferably G) that I can flash or verify against? And does anyone know how to place the 80662A display in the test pattern mode? I saw a handful of boards including the CPU sell for about $30-60 last week on ebay, which I am very sad I missed out on now, as it was before my SA arrived. The tools I have at my disposal at the moment are a DMM, variac, tek 2430 oscilloscope, arduinos, and two HP 16500 LAs with an array of cards. I would be willing to trade a 16500A with misaligned front floppy and 16510A card for a CPU board.

author: KE5FX
author_rank: Super Contributor
timestamp: June 17, 2020, 02:08:18 am
content: Where are you located? I may have a spare CPU board somewhere, not 100% sure but I can look. The firmware can be downloaded from the 'Manuals' section athttp://www.ko4bb.com. As far as I'm aware you can just put the latest available firmware on there.Disregard any notes in the firmware about not being able to use CMOS EPROMS, I had a really crappy EPROM burner at the time...

author: pnv57
author_rank: Contributor
timestamp: June 17, 2020, 02:26:22 am
content: Quote from: KE5FX on June 17, 2020, 02:08:18 amI will PM you on that. Thanks for the link, it is incredibly useful. I will be verifying the EPROMs tomorrow hopefully, and I do not own a burner (yet). Any leads on the PAL? Or do they just not fail? That worries me, because it is a programmed chip.

author: KE5FX
author_rank: Super Contributor
timestamp: June 17, 2020, 02:49:10 am
content: Quote from: pnv57 on June 17, 2020, 02:26:22 am95% of the time, the problems I've seen with the CPU board have come down to seating it properly and ensuring good connectivity of the massive ribbon cable that hooks up to it. It's a little strange that the PAL is the only thing showing up on IR, but to date, I haven't seen any of the PALs fail. EPROM failures are much more common, and even they aren'tthatcommon.

author: 0culus
author_rank: Super Contributor
timestamp: June 17, 2020, 02:51:46 am
content: Quote from: KE5FX on June 17, 2020, 02:49:10 am[emphasis mine] this. this. this.Before doing anything drastic, OP, you should pull the board(s) and reseat them. Do the same with the ribbon cables. You'd be surprised how often a simply mechanical 'intervention' solves the problem.

author: tkamiya
author_rank: Super Contributor
timestamp: June 17, 2020, 03:00:25 am
content: And small amount of Deoxit does wonders too!

author: pnv57
author_rank: Contributor
timestamp: June 17, 2020, 05:33:16 am
content: Quote from: 0culus on June 17, 2020, 02:51:46 amFirst thing I tried. I've pulled the CPU to check the capacitors and resistors as well as get a better thermal photo a few times now. I also pulled the front panel interface (forgot the A#). I did the eraser trick on the oxidized looking pins, and no dice. Tomorrow I will look them up in the manual and see if the residual oxidation could be causing issues. After servicing a few Tektronix 22xx and 24xx scopes, the cards and frequent test pins are a welcome sight.

author: miken
author_rank: Regular Contributor
timestamp: June 17, 2020, 07:39:37 am
content: Take a look at the 85662A manual section A3 for the ROM self-test. You have to make a few jumper connections.

author: tkamiya
author_rank: Super Contributor
timestamp: June 17, 2020, 03:32:25 pm
content: I have a stack of 8568B and 85662A. I can part them out for you if you'd like. I'll give you parts. You just pay for shipping. You can have the whole thing if you want to drive to Florida (come pick them up). Sorry, but I cannot ship.Also, please make sure cables are good. On mine, Centronics male side was flattened so much that it wasn't making good contact.

author: pnv57
author_rank: Contributor
timestamp: June 17, 2020, 04:57:50 pm
content: Quote from: miken on June 17, 2020, 07:39:37 amJust gave it a shot, nothing happened even when I jumped the CRT start pins. It smelled a little burney, and the only chips getting warm (105F) were the U4-7 ROMs on the A3A6 Controller. All the front panel lights turn on, except for the "Sweep" LED, which looks like it would be green. Looks like the display will be next after getting the 8566B repaired or replaced.

author: pnv57
author_rank: Contributor
timestamp: June 17, 2020, 08:56:23 pm
content: Update: EPROMs all check out, I verified against known the known good firmware images.

author: KE5FX
author_rank: Super Contributor
timestamp: June 18, 2020, 04:17:06 am
content: Quote from: pnv57 on June 17, 2020, 08:56:23 pmPM sent.