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KLund1
November 4th, 2017, 11:54 AM
I have 2 dead 5150's, (both 64K-256K MB) need some help with additional diagnostics.
What I have done for both:
tested PSU output with multimeter, 5v and 12v show ok. PSU fans spin.
Checked MB switches from this site. All set to correct settings.
http://www.minuszerodegrees.net/5150/misc/5150_motherboard_switch_settings.htm
Tested color video card in working 5160, and it is good showing on a 5153. I have just the one card to test both 5150's
5150 #1 with just a color video card and floppy controller, & keyboard, when the power is switched on, gets a quick black screen (< 1 second) then goes to white.
5150 #2 with just a color video card and floppy controller, & keyboard, when the power is switched on, screen just stays white, but here a small click from speaker.
Nothing after that. I let both stay on for 5 minutes, waiting for a beep, but nothing. No bad smells after being on that long.
I reseated all socketed IC's for both, no change.
I swapped socketed IC's one at a time to test, no changes. All behaviors the same.
I pulled the working PSU from the 5160 (Astec AA12150), and connected to #1, same response when power turned on, but got a slight wiff of ozone from PSU, and shut it off. The AA12150 has an extra wire on the P8 connector, 2'nd from back of MB. Also some color of the wires are different. Not sure if that make a difference. The AA12150 powers 2 FD, and HD in the 5160.
Suggestions on where to go from here?

Multisync
November 4th, 2017, 12:07 PM
http://www.vcfed.org/forum/archive/index.php/t-33614.html

modem7
November 4th, 2017, 12:18 PM
Nothing after that. I let both stay on for 5 minutes, waiting for a beep, but nothing.


... but here a small click from speaker
Some 5150 motherboards are known to produce that click. Ignore it.


tested PSU output with multimeter, 5v and 12v show ok. PSU fans spin.
What about the POWER GOOD line out of the PSU. If that line does not go active, the motherboard will not start. See web page at [here (http://minuszerodegrees.net/5150_5160/MDC/no_beeps_2.htm)].


I pulled the working PSU from the 5160 (Astec AA12150), and connected to #1, same response when power turned on, but got a slight wiff of ozone from PSU, and shut it off. The AA12150 has an extra wire on the P8 connector, 2'nd from back of MB. Also some color of the wires are different. Not sure if that make a difference.
- The 5150 and 5160 have the same pinout on the power connectors.
- The extra wire is not a problem for the 5150 or 5160 (see [here (http://minuszerodegrees.net/5150_5160/misc/5150_5160_use_of_5170_psu.jpg)]).
So it is okay to move the 5160 PSU into the 5150s.

Stone
November 4th, 2017, 12:36 PM
Remove P8 from the motherboard and turn it on. does that make any difference?

modem7
November 4th, 2017, 12:55 PM
If there was a short circuit tantalum capacitor, I expect that it would overload any PSU connected, resulting in the PSU shutting down (i.e. no output voltages).
Because the OP is seeing +5V, I have have ruled out a short circuit tantalum capacitor.

To start, the 64KB-256KB version of the 5150 motherboard needs only +5V and POWER GOOD
12V, positive and negative, is not needed by the 5150 motherboard.
A lack of -5V will not prevent the 64KB-256KB version of the 5150 motherboard from starting (although it will cause a 131 error later).

KLund1
November 4th, 2017, 01:15 PM
What about the POWER GOOD line out of the PSU. If that line does not go active, the motherboard will not start. See web page at [here (http://minuszerodegrees.net/5150_5160/MDC/no_beeps_2.htm)].

This is just I need!!!
Tested through those instructions, 1 dead PSU #1, 1 bad MB cap on #2
Is there a similar link to finding where the fault is in a PSU. Yes I'll be very careful what I touch.

modem7
November 4th, 2017, 01:55 PM
Tested through those instructions, 1 dead PSU #1, 1 bad MB cap on #2
That sounds like you used the complete diagnostic procedure, at [here (http://minuszerodegrees.net/5150_5160/MDC/minimum_diag_config.htm)].

Lots of IBM 5150 information at http://minuszerodegrees.net


Is there a similar link to finding where the fault is in a PSU. Yes I'll be very careful what I touch.
IBM did not consider the 5150 PSU to be repairable. They did not release circuit diagrams. Also, there were different versions of the 5150 PSU.

The answer to your question is, 'Not at minuszerodegrees.net'. There may be other resources on the Internet.

Considering that you described the PSU as 'dead', one quick thing to check is the fuse inside. It may have blown due to age. Before you open up the PSU, read the 'Power supplies' section of the web page at [here (http://minuszerodegrees.net/safety/IBM_51xx_hazards.htm)].