68kMLA Classic Interface

This is a version of the 68kMLA forums for viewing on your favorite old mac. Visitors on modern platforms may prefer the main site.

Click here to select a new forum.
Hanging Out with a pack of Wombats
Posted by: Phipli on 2024-01-16 08:55:39 I recently picked up three Wombats (Centris 650, Quadra 650 and Quadra 800) boards for my dad, sold not working. I thought I'd try to document the repairs a bit more than usual. Just ramblings, I'm not stuck (yet), please don't fill the thread with preemptive suggestions. The boards are basically all the same PCB, but I basically have one of each case badge. I'll call them #1, #2 and #3 in order of how premium they were as sold. Boards are as follows, using @joshc's photos if he doesn't mind. #1 - Quadra 800 8MB soldered 60ns RAM, ROM slot fitted, clocked at 33Mhz. Ethernet. 55MHz 88916. Speaker heater at J27. LED header fitter at J25. 820-0380-A 20th week of 93 Battery damage. #2 - Quadra 650 8MB soldered 70ns RAM, No ROM slot, clocked at 33Mhz. Ethernet. 55MHz 88916. Speaker header fitted at J26. 820-0380-A 31st week of 94 No video output. #3 - Centris 650 4MB soldered 80ns RAM, ROM slot fitted, clocked at 25Mhz. No Ethernet. 55MHz 88916. Speaker header fitted at J26. 820-0380-04 30th week of 94... Or, the 54th?! week of 92. Two labels. Given this is a preproduction board, 92 makes more sense, but last time I checked there were only 52 weeks in a year? Condition unknown.
Posted by: hauke on 2024-01-16 09:10:21 #2 - Quadra 650 -- They seem to do that... my Home Mac is a '650 with two MacPicasso 340 cards, and I only accidentally noticed that the long-unused onboard video was dead.
Posted by: Phipli on 2024-01-16 09:14:00 Boards arrived today, I've looked over the three, and other than grime, there is only visible damage on #1, the Quadra 800. I thought I'd start there. At some point, the battery leaked and the battery holder is missing. Some of the RAM chips show signs of corrosion. As the damage is pretty much limited to one of the two (4MB each) banks, for now I decided to desolder one bank and see where it gets me. After removing half of the RAM, I checked the continuity of the vias which were closest to the battery and found that two don't conduct. These will need neater repairs, but for now I will circumvent them with bodge wires for testing.
Posted by: Phipli on 2024-01-16 09:18:02 #2 - Quadra 650 -- They seem to do that... my Home Mac is a '650 with two MacPicasso 340 cards, and I only accidentally noticed that the long-unused onboard video was dead. I'd suggest checking the DJMEMC for pins that have come free of the board. If it was graphical artifact issues, I'd check the 74245s and for dry joints on the VRAM, given how close they are to the power connector. I've not had a look at #2 yet. Hopefully I've just made some progress with #1. Wish I could find my power cable extender, I can't see it anywhere.
Posted by: ClassicGuyPhilly on 2024-01-16 09:54:09 Definitely points for creative thread title, good luck with the work! Here's some tunes to go with the effort, including special guest appearance by Abe Vigoda - I was at this show.
Posted by: Phipli on 2024-01-16 10:00:14 Update on Wombat #1 View attachment 1000015742.mp4 Nearly dinner time so I'm not going to test beyond this, but a chime is always good 🙂 Definitely points for creative thread title, good luck with the work! Here's some tunes to go with the effort, including special guest appearance by Abe Vigoda - I was at this show. Thankyou 🤣
Posted by: joshc on 2024-01-16 11:49:09 Nearly dinner time so I'm not going to test beyond this, but a chime is always good 🙂 Woop woop.
Posted by: Phipli on 2024-01-16 12:00:50 Quick check of board #3 (Centris, no ethernet). It chimes ok, I'll test them both with video in the morning. View attachment 1000015744.mp4
Posted by: joshc on 2024-01-16 12:06:19 Quick check of board #3 (Centris, no ethernet). It chimes ok, I'll test them both with video in the morning. View attachment 68223 That one might be fine. It’s in the best physical condition. I just couldn’t remember if it works or not.
Posted by: Phipli on 2024-01-16 12:08:04 As an aside, I suspect this (board #3) is pre-production given it has a -04 revision instead of a letter. I made a mistake in my description, it is fitted with both speaker headers, and the LED header. It has two barcodes, one that says *E as the factory - is this evaluation? The second is for SG which I'm guessing is Singapore. The SG sticker is the very end of 1992, which is before the Wombat was released. Lastly, the silkscreen says "Wombat". They don't normally say this 🙂
Posted by: Phipli on 2024-01-16 12:09:59 That one might be fine. It’s in the best physical condition. I just couldn’t remember if it works or not. Understood - I thought it might be the case. It is a nice board. If I really wanted I could add the extra 4MB and ethernet... But I don't want to harvest the needed parts from a comm slot ethernet card because it would be a waste. The 4MB RAM might be worth it though.
Posted by: eharmon on 2024-01-16 20:16:08 #1 - Quadra 800 8MB soldered 60ns RAM, ROM slot fitted, clocked at 33Mhz. Ethernet. 55MHz 88916. Speaker heater at J27. LED header fitter at J25. Ah hah more with only 55MHz 88916s. But the C650 doesn't make sense either! The 2X_Q output does not meet the stringent duty cycle requirement of the 20 and 25Mhz 68040 microprocessor PCLK input. The 88920 has been designed specifically to provide the 68040 PCLK and BCLK inputs for the low frequency 68040 microprocessor. Wish I could find specs on the XC88916, despite the 55MHz rating it doesn't seem to behave like the final MC mask....or the C650 boards were shipped with out of spec parts.
Posted by: Phipli on 2024-01-17 09:41:40 Today's updates... Wombat #1, the Q800 with a lobotomy, has been confirmed to be getting as far as the question mark. This is good. I suspect it will be fine. I just need to tidy up my bodge repairs and perhaps put some RAM back on it to put it back to 8MB. Wombat #3, the Centris 650, also has good video out and I suspect is fine. Here it is photographed with a thermal camera. Wombat #2, the Quadra 650 with suspected bad video. I powered it on and photographed it with a thermal camera to see if all the chips got warm. This is to see if everything is getting powered and possibly clocked ok. It isn't a perfect technique, but useful. Spot the difference between the two, there is one visible. I also checked if the 31.3344MHz clock was working and it seems to be. Since everything looked ok, I plugged in a monitor and checked. No video, but when I wiggled the connector, I got cycling video. It is as if the monitor is struggling to sync or something. I have drowned it in contact cleaner for now, but some reflowing might be needed. We'll find out. Any video at all is a good sign!
Posted by: ClassicGuyPhilly on 2024-01-17 10:02:31 Nice work taming the Wombats, and love the thermal pix too!
Posted by: Melkhior on 2024-01-18 04:48:10 Would you have similar pictures of the back of (one of the) board(s)? I'm checking which termination packs of resistor related to the '040 are connected, and how the output buffer are set up (resistor R17{5,6,7} and R22{1,2,3}). I do have Wombats but installed in cases will all the trimmings, if you can spare the time to take a picture or two while you have them out I would be grateful 🙂
Posted by: GRudolf94 on 2024-01-18 07:31:09 Would you have similar pictures of the back of (one of the) board(s)? I'm checking which termination packs of resistor related to the '040 are connected, and how the output buffer are set up (resistor R17{5,6,7} and R22{1,2,3}). I do have Wombats but installed in cases will all the trimmings, if you can spare the time to take a picture or two while you have them out I would be grateful 🙂 I'm guessing they'll be in small buffer mode (R17{5:7] populated) - LC040s do not implement large buffers. I recall looking at that when gawking at my own Q800 board, but my brain threw out the notes on it.
Posted by: Phipli on 2024-01-18 07:42:46 Would you have similar pictures of the back of (one of the) board(s)? I'm checking which termination packs of resistor related to the '040 are connected, and how the output buffer are set up (resistor R17{5,6,7} and R22{1,2,3}). I do have Wombats but installed in cases will all the trimmings, if you can spare the time to take a picture or two while you have them out I would be grateful 🙂 I'm guessing they'll be in small buffer mode (R17{5:7] populated) - LC040s do not implement large buffers. I recall looking at that when gawking at my own Q800 board, but my brain threw out the notes on it. Sorry, I've been distracted. I'll grab a photo shortly.
Posted by: finkmac on 2024-01-18 07:44:16 by the way, what is the code on these fuses? Trying to find replacements.
Posted by: GRudolf94 on 2024-01-18 07:47:18 View attachment 68343 by the way, what is the code on these fuses? Trying to find replacements. They're probably gonna be 500mA or 1A. One is for termination power on SCSI, the other is for transceiver power on AAUI.
Posted by: Melkhior on 2024-01-18 07:50:28 I'm guessing they'll be in small buffer mode (R17{5:7] populated) - LC040s do not implement large buffers. I recall looking at that when gawking at my own Q800 board, but my brain threw out the notes on it. Probably, but only Centris 650 have LC040 IIRC - Quadra 650 and 800 have full '040. I'm trying to understand the signal termination requirements of the MC68040, and it seems Apple has done it all: I can't see any termination for A/D on the Q900 schematics, it's present but labelled "for 40 MHz operation with large buffer" for Q650/Q800 (which I'm trying to confirm are always using small buffers and no termination), and are always present/large buffers on the 840AV...
1 >