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BA23 Cooling and Power Supply Questions

vaxorcist

Experienced Member
Joined
Apr 26, 2012
Messages
59
Location
Germany
I have several BA23 enclosures with differing cooling assemblies and power supplies.
I'm not sure everything is still as it once was when it was sold.

Questions concerning the BA23 cooling and PSUs:

Where/when and in what combinations were the following cooling options used:

- With/without fan speed control (70-22643-01; regulates from 5.9 V [cold] to 10.3 V [warm] with 12 V input)

- With/without front fan baffle/cowling (70-21506-01)

- Full/reduced fan voltage (4 possible H7864 settings; 12.2 V, 11.5 V, 10.8 V, 10.1 V)

What are the differences between the three PSU versions (besides the known 12 V 6A/7A)?

Known facts:

A sticker under the PSU tells that the fan speed control is to be used with the 12 V setting only
(which makes sense)

Assumptions:

The front fan baffle/cowling accomplishes that most of the front fan cooling effect is concentrated on the PSU and card cage; the cooling of the two drive bays at the front of the BA23 will get worse because of that.

A fully loaded card cage with power consuming modules might be a reason to use the baffle.

Using an RD53 and a TK50 in the front drive bays might require more intensive cooling directed to the bays by not employing the baffle.

Quotes on the baffle:

EK-186AA-MG-001 BA23 Enclosure Maintenance.pdf 10/88

Page 3-24:
"On some systems, remove the fan baffle and baffle holder from the front fan."

Page 3-31:
Figure 3-20: Accessing the Front Fan: "OLDER SYSTEMS ONLY" [relates to the baffle removal]

EK-MIC11-SG-001 MicroPDP-11 Systems-2.pdf 09/85

Page 8-32:
"Remove the fan cowling and cowling holder (if present)."

Three versions of PSU H7864:

H7864 (30-20444-00) 5V, 36A / 12V 6A
H7864-A (30-21749-01) 5V, 36A / 12V 7A
H7864-B ???

Quotes on the PSU versions and fan voltage settings:

EK-186AA-MG-001 BA23 Enclosure Maintenance.pdf 10/88

Page 1-14:
"There are three variations of the power supply, depending on the enclosure model number: H7864, H7864-A, or H7864-B."

"The power supply has also two +10 Vdc at 0.45 A fan outputs for the front and rear dc fans. You can increase the fan voltages to 12 Vdc by changing a power supply jumper. However, the KA630 CPU module's thermal and acoustical specifications are based on the +10 volt setting."

Page 3-2: Table 3-1 BA23 FRUs

??? Who can shed some light on this ???

Regards,

Ulli

P.S.
Has anyone got the H7864 Maintenance Print Sets?
I'm also looking for the "MP02065-01 630QY Field Maintenance Print Set" which was available in pdf format on the Internet some time ago, but isn't any longer yet
 

RSX11M+

Veteran Member
Joined
Feb 14, 2011
Messages
1,075
I don't have answers to your in-depth questions about these variations of the BA23. I was unaware of a variable speed fan version.

However I too am interested in the print set of the H7864 should you locate one.


I will be watching this thread with great interest.
 

Lou - N2MIY

Veteran Member
Joined
Apr 1, 2008
Messages
1,306
Location
Albuquerque NM / Potomac MD
Ulli,

I have four H7864s here, and none of them have variable speed fans. These are/were in BA23s that started life as Micro 11/23, 11/73, and uVax II.

I too would very much like a print set for H7864! These all seem to have been made by Astec.

Lou
 

vaxorcist

Experienced Member
Joined
Apr 26, 2012
Messages
59
Location
Germany
Fan Speed Control

Fan Speed Control

I found the fan speed control mostly on newer BA23s, e.g. a VAXstation 3200 from 1990. It is not part of the H7864 PSU but a separate PCB.

Fan Speed Control small.JPG

It is attached (via a bracket) to the rear fan and can thus meter the temperature of the air passing by.

I assume that it was meant to reduce the noise level, not the energy consumption (saving energy wasn't that important back then).
I don't know (yet) whether all fans support being speed controlled; on the ones I have at hand at the moment it says: operating voltage range 5.5 to 14 volts.

Ulli
 

vaxorcist

Experienced Member
Joined
Apr 26, 2012
Messages
59
Location
Germany
Reduced fan voltage

Reduced fan voltage

The jumper for the reduced fan voltage is hidden inside the H7864. You have to remove the PSU from the BA23 to access it.

With the H7864-A the jumper (J13, detached from pin 3) can be found at the front end of the PSU towards the card cage, see:

JumperA-small.jpg

With the H7864-B it is placed where the front fan protrudes into the PSU, see:

Jumpers.JPG


I think at least all BA23s/H7864s from the start of the MicroVAX II have this jumper; I don't know about earlier ones (probably the H7864 version without suffix; mine are -A or -B).

Ulli
 
Last edited:

vaxorcist

Experienced Member
Joined
Apr 26, 2012
Messages
59
Location
Germany
More PSU / cooling knowledge ...

More PSU / cooling knowledge ...

By having a closer look I found out that:

H7864 and H7864-A are both ASTEC made, whereas the H7864-B was manufactured by DEC.

The Edited Modules and Options List '91 specifies the H7864-B as: "THERM PROT" which sounds like "thermal protection/protected".
I don't know whether that refers to the fan speed control or an extra (unknown) feature of the PSU itself.

With both H7864 and H7864-A the cable for the rear fan is part of the PSU, the front fan is connected with an extra cable plugged into the PSU front.
Most H7864-A front fans seem to have the baffle attached.

The H7864-B does not have an integrated cable for the rear fan, both fans are connected via the fan speed control PCB and a special cable assy.
The fact that you cannot connect the rear fan without the fan speed control cable assy leads to the conclusion that all H7864-B PSUs use the fan speed control.
None of my H7864-B front fans employs the baffle.

This is the sticker telling how to configure the fan supply voltage for use with the fan speed control:

Sticker small.jpg

The blurredness is NOT the photo, the sticker quality is that bad!


Ulli
 
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