AK6DN
Veteran Member
Given that voltage drop under load, I would suspect oxidized connectors that have a higher than normal resistance, giving a substantial voltage drop under load.
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M8189 bootstrap error LED's D1 and D4 on
- Thread starter cmao
- Start date
cmao
Experienced Member
Are BDCOK and BPOK used as "remote sensing" that feedbacks local remote voltage back to power source ? If the returned voltage is too low then the power source will pump more voltage. Is it correct ?
cmao
Experienced Member
It is part of my investigation as well. Thanks for the comments.
AK6DN
Veteran Member
No, they are just logic levels. H is power DC or AC OK, L is power not ok.
daver2
10k Member
No, they just indicate that the voltage rails are at the correct voltage.
They are generated by the power supply and signal the computer.
Dave
cmao
Experienced Member
Before I move forward to inspect the paths of power supply that currently powers my PDP-11. I need to insure that my M8189 is functional so I bypass the +5V source to an independent power source with adjustable +5V +/- 1V. I set it to +5.6V so the Vcc pins on most TTL chips are ~+5V. I set M8189 to "RUN" followed by "RESTART". The result is very encouraged. I have never seen the output of M8189 (see attached). I would conclude that my M8189 is working and there is a ~0.6V drop from M8189.
wa2flq
Experienced Member
If you ha
I would only use this configuration (+5.6V) briefly until the cause of the .6v drop is remediated. The maximum TTL supply voltage specification is 5.25. Dodgy connections are by definition unreliable. Test of course at lower supply voltages where possible.
You may need some type of load, but never leave the costly or rare boards in the bus as you search the for bad supplies or connections.
Agreed.
I would only use this configuration (+5.6V) briefly until the cause of the .6v drop is remediated. The maximum TTL supply voltage specification is 5.25. Dodgy connections are by definition unreliable. Test of course at lower supply voltages where possible.
You may need some type of load, but never leave the costly or rare boards in the bus as you search the for bad supplies or connections.
pbirkel@gmail.com
Veteran Member
Nice job :->. Can you share the gerber file-set for the adapter, please?
cmao
Experienced Member
Here is the gerber file set. Carefully select pins not to damage the sockets on MP8189 and cut the extruded parts of the pins as shown in the picture. There are two 10k ohms needed as shown in the picture. Good luck.
pbirkel@gmail.com
Veteran Member
Thank you 'cmao' :-}. I don't think that I've ever seen that style of pins; what are they called and where did you acquire them?
cmao
Experienced Member
I don't recommend round style pins because the sockets will be damaged. Those flat and thin are recommended. Those shown in picture are recycled pins and just the example.
cmao
Experienced Member
jmdhuse
Experienced Member
Modern ATX power supplies provide most the current to the 12V supply... check to see how much current yours can provide on the 5V supply. I'm looking at a 400W supply right now that provides 3.3V @ 12A, 5V @ 12A, and 12V @ 28A.
jplr
Experienced Member
> 5V @ 12A, and 12V @ 28A.
Usually, circuits use much less current on 12V than on 5V.
Maybe you wanted to write
5V @ 28A, and 12V @ 12A?
Even 12V@12A looks a lot. The LSI-11 user manual lists 3.1A for a typical configuration (page 2-4)
Usually, circuits use much less current on 12V than on 5V.
Maybe you wanted to write
5V @ 28A, and 12V @ 12A?
Even 12V@12A looks a lot. The LSI-11 user manual lists 3.1A for a typical configuration (page 2-4)
Last edited:
cmao
Experienced Member
My 225W AXT provides +5V@22A, +3.3V@18A, +12V@16A.
daver2
10k Member
Just out of interest, how many separate wires (of what gauge) connected the original ATX supply to the PC, and how many have been connected between the ATX supply and the PDP?
How are the cables terminated on the PDP backplane?
The voltage drop across a cable is directly proportional to the current flowing and cable resistance. The cable resistance increases with length and decreases with cross-sectional area (CSA). The CSA is proportional to the number of individual strands of wire, and the area of each strand.
In addition, all this can be undone by not terminating the cable correctly...
Dave
How are the cables terminated on the PDP backplane?
The voltage drop across a cable is directly proportional to the current flowing and cable resistance. The cable resistance increases with length and decreases with cross-sectional area (CSA). The CSA is proportional to the number of individual strands of wire, and the area of each strand.
In addition, all this can be undone by not terminating the cable correctly...
Dave
jmdhuse
Experienced Member
No, I meant what I said... modern motherboards take the 12V as the source for the switching regular that provides the massive 1.8V current to the processors...
jplr
Experienced Member
@cmao, you should make a diagram and provide measurements to make clear for everybody what you measure.
I would measure +5V in three places:
- At the ATX power connector
- At the cable sending power to your backplane
- At the rear of the backplane
- On one board (on one IC)
For a classical LSI-11 it would be something like this:
I would measure +5V in three places:
- At the ATX power connector
- At the cable sending power to your backplane
- At the rear of the backplane
- On one board (on one IC)
For a classical LSI-11 it would be something like this:
jplr
Experienced Member
jmdhuse
Experienced Member
Correct, but if he is using a modern ATX supply for his vintage computer, this might be the case... Maybe I missed where the power supply he is using is identified...