Workgroup Server 9150 internal video not working

[james_w]

So I've been restoring a couple of WGS 9150s. One is an original (80mhz) and the other a 9150/120.

The 9150/80 was exhibiting these issues regularly:

• crashing with type 1, type 2, and type 3 errors after some usage
  
• internal video sometimes had random pixels of noise (in random colours) here and there
  
• occasionally the internal video also didn't work, just a black screen on boot
  

I figured this was all probably RAM related. I removed all the SIMMs and the problems were still there. So then I suspected its 8mb of DRAM soldered to the board.

At this point I decided I might as well replace the 18 electrolytic caps on the logicboard and give it a good clean. The insides were rammed with dust and fluff! I think this machine had sat on someone's floor for years just sucking in all the dirt. It was quite a gross job.

Anyway it's all clean and has shiny new caps installed.

Now it doesn't seem to crash any more, but I get no internal video on boot, just a black screen. My monitor (an NEC 1880FX) knows there's something there as it comes off standby when I boot the machine, but it never gets a full signal.

(as a side note - video works fine from a Nubus card)

Anyone got any ideas? I suspect one or more of the DRAM chips has failed... or something else?

I've searched for schematics in vain. Not sure where to go next diagnosing this.

 

[Unknown_K]

IS that a LCD monitor, if so try a CRT. 

Video: supports thousands of colors at 512 x 384 and 640 x 480, 256 colors at 832 x 642

Try finding a PDS video card which will give you more options for resolution and refresh rates.

 

[james_w]

It is an LCD, but worked absolutely fine at 832 x 642 with it until now.

The video works fine from a Nubus card, and may well do from a PDS card too, but I'm trying to fix the *internal* video

 

[Unknown_K]

Check the video adapter to see if you changed the settings.

I don't have a 9150 and the only motherboard pics I can find are for a "prototype" but that shows a capacitor next to the video out and that might need replaced.

 

[james_w]

The adapter I use has no settings or switches, just a pass through.

I've replaced all the capacitors - see my original post.

Thanks for the suggestions, I think it's more likely a faulty chip or a damaged trace somewhere on the board. I'll keep looking!

 

[Franklinstein]

Do you have a PDS card or the PDS terminator installed? Supposedly these things have problems if the slot is left open.

 

[james_w]

Do you have a PDS card or the PDS terminator installed? Supposedly these things have problems if the slot is left open.

Thanks for checking about that. I do have the PDS terminator installed. Sometimes on startup the computer reports a problem with the cache card. So I'm wondering if I need to give all the contacts in the ROM, Cache, and PDS slots a really good clean. If they're a little corroded perhaps the cards aren't always being seen, and could be the cause of the issues I'm seeing.

I'm going to give it another try later today.

 

[Franklinstein]

Right. Sounds like you're probably on the right track. I don't have any other quick fix suggestions here. The G1 Power Macs were a little touchy sometimes and age hasn't done them any favors. Have you done anything with the power supply? The OE units are quality and pretty heavy-duty but even those could need new caps after nearly 30 years. 

 

[trag]

Have you cleaned and replaced the heat sink grease on the CPU?   At that age, it's probably a white crust, not doing its job any more.

I have seen similar issues on 7100 machines which cleaning and replacing the CPU heat sink compound fixed.   The CPU overheats very quickly without good compound.

If you do replace it, be very gentle.  The CPU is fragile and can be cracked with undue pressure.  Also, do not overapply the replacement grease.    Too much and it can run off the CPU onto the pins and cause shorts.

 

[Franklinstein]

I have seen similar issues on 7100 machines which cleaning and replacing the CPU heat sink compound fixed.   The CPU overheats very quickly without good compound.

If you do replace it, be very gentle.  The CPU is fragile and can be cracked with undue pressure.  Also, do not overapply the replacement grease.    Too much and it can run off the CPU onto the pins and cause shorts.

I once bought an 8100 board and its heatsink compound (the dry yellowish mess we all know and love) was misapplied from the factory: only half of the die had compound on it, the rest splattered uselessly over the top of the package. I'm not sure how the thing continued to operate but since it was received as parts it may not have.

These chips (and some IBM-produced 603 and 604 QFPs) are very pretty but they're very fragile: they use a flip-chip technique to attach the die to a ceramic substrate after which the top is filled in with epoxy (normally blue but yellow was sometimes seen on early examples). Sometimes the old thermal paste will discolor the epoxy and overly aggressive cleaning and/or harsh chemical cleaners will eat away at the epoxy a bit. The pins are also basically glued in place on the edges of the package which makes these a little difficult to rework.

 

[james_w]

Thanks for your tips @trag and @Franklinstein, I don't think replacing the CPU heatsink compound would ever have occurred to me as a thing to fix. I think I've only done it once before many years ago.

Sounds like I'd better be very careful!

Time is super limited right now, but hopefully I can give that a go sometime in the Autumn