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DEC 5133 has no POST

maelstrm

maelstrm

Experienced Member
Joined
Jun 6, 2022
Messages
109
Location
Raleigh, NC
Greetings, Federation,

I have come across a DEC 5133 (for free!). Unfortunately, it won't POST. I didn't test with its original power supply, but with a standard (known good) AT power supply. There are no beeps from the original speaker. The front power indicator LED lights up. An attached keyboard flashes its CAPS/NUM/SCROLL LEDs on power on.

Here's what I tried so far:

  • Re-seating CPU
  • Using an ISA video card
  • Removing all memory modules
  • Putting a load on the PSU (an old IDE hard drive just to draw some current)
  • Clearing CMOS password and setting "Recovery Mode" using J10 and J11.
  • Using an ISA POST card shows no codes (only - - - -).
  • I don't see any blown caps. But some of these are tantalum.

Here's what I haven't tried:
  • Re-seating the riser card, or removing it altogether
  • Replacing the Dallas RTC chip (I'd have to order some flavor of replacement)
Any other ideas???

Thank you!
 
Did you measure the resistance between the power rails on the motherboard power connector (with everything disconnected)? If there's a bad tantalum you may see a short across one of the voltage rails at the power connector, then you can move in from there and try to identify which one it is on the board.

can't hurt to remove the riser board.

I wouldn't think that a dead Dallas RTC clock would prevent boot, I think most systems are better off with a dead Dallas RTC than with nothing.
 
What sort of DEC 5133? I assume some model of Celebris, Venturis, Prioris, perhaps one of their laptops...

The DEC Venturis 5xxx (excl. 560) at least doesn't seem to detect a flat RTC battery and reset configuration to defaults - you just get random potentially invalid configuration which I've seen result in the machine rebooting mid-POST and displaying crazy settings the UI wouldn't let you pick if you get into the BIOS setup utility. So if the RTC chip hasn't been replaced or modified to use an external battery at some point in the last decade I wouldn't be surprised if it was the source of the problem.
 
Thanks for the replies. I can check for a shorted tantalum.

The machine is the Venturis 5133. As far as I can tell, the RTC chip is the original. Would a modern 12887 work in this board? I'm a little worried because the POST card has no activity. I don't get any blinking keyboard LEDs (after the initial flash), which one might expect if the board is resetting.

I sure hope I can get it to work. It's a really nice machine (not that I need another!

Thank you!
 
My Venturis 5133 had a DS12887 already in it. Rather than replacing it though, I just severed the connection to the internal battery and added on an external one:
mb-v2.jpg
 
I finally had time to take the riser card out and it booted up normally. I then put the riser card back in + the sound card and it still works. I'm going to assume the ISA modem has a short (I haven't put it back in), or there was a temporary issue with the riser itself that resolved the problem.

This is such a cool machine, but its shape is a little rough. There's no cracks in the plastic, but there's some rust inside and out. It's also missing the "digital" emblem on the front (but the Venturis emblem is still there at least). The VRAM sockets are empty, and someone removed an ISA card at some point. But it POSTs! I'm so stoked about this thing.

I'll post some pics later. Thank you all!
 
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