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Dan,

The change occurred in the April 25, 1985 update:

"Change B1 from 3160-0209 to 3160-0450 FAN-24VDC, 36 CFM"

The closest I could find in today's market is the EBM Papst 8124G. This fan has a specification of:
35 (not 36) CFM
38 dBa
18 - 30 VDC.

I also found this fan in several 5335A counters installed at the factory by HP, so I figure it's the right one. I found some for about $22 in an online search.

The 8124K is the ball-bearing equivalent to the 8124G, which is sleeve bearing.

Hope that helps!

Regards,

Joe

Wow, I can't imagine that any engineer who was able to get hired by HP
wouldn't understand why JPG isn't appropriate for screen shots or other
line art. (or anything else that isn't a continuous-tone natural scene,
which is what JPG was designed for, and the only thing for which it
works well)

The options weren't great back then, unfortunately. The .PNG spec was brand new and hadn't caught on yet. Unisys was shaking everyone down for royalties on the .GIF patent. I'm not sure .BMP existed at that time -- I believe it did, and it would have worked, but it was mostly a Windows-specific format. Dunno if the Unix and Mac people would have been happy with that. .TGA and TIFF would have worked but the files were large and cumbersome, and as I recall they weren't used widely outside the desktop publishing business. .PCX and .LBM would have worked well since RLE compression is a good fit for this type of file, but again they didn't have a lot of support across different platforms and industry sectors.

So that left .JPG. While definitely not the 'right' format, if you crank the quality level up high enough, it could yield tolerable results, and unlike .GIF it could be freely implemented. Arguably HP should have paid the danegeld for the .GIF license and called it good, but it's hard to second-guess them at this late date.

-- john, KE5FX

On Tue, Mar 19, 2019 at 07:22 PM, Joe / KN5U wrote:

By the way, the original fan was 120 VAC, but repair note changed the fan to 24 VDC. This was precipitated by the power supply relay and socket overheating. The repair note had a description of a circuit mod using a diode and also replacing the fan and socket. I have done a few of these mods and this a fairly simple fix. Let me know if you need a copy of the change.

Joe, KN5U

I have looked extensively, but have not found a 24V fan with the necessary airflow specs that also had quieter operation than the fan already in the unit. You mention that you have done some mods to change the fan from 110V AC to 24 V DC. What fan did you use as the replacement and do you happen to know its airflow/noise specs?

Thanks,

Dan

On Fri, Mar 22, 2019 at 03:04 PM, Adrian wrote:

Yup, that's the one, not as nicely made as the HP original but it dropped straight in and is still running! I'm not using the 8566A as much as I was these days so I find I need to fire it up for a few hours each week to keep the battery topped up but it does the job. Modifying it so it charges in 'standby' has been on my list for a few years ... I'll get there one day....!

Awesome, thanks! My battery is completely dead, even running it for a few hours won't charge it. Hope you share the modification if you ever get around to it. :o)

Sean

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Not sure about that one, it came out of the 1500MHz plug-in SA hat Fi he HP180 scope

Yup, that's the one, not as nicely made as the HP original but it dropped straight in and is still running! I'm not using the 8566A as much as I was these days so I find I need to fire it up for a few hours each week to keep the battery topped up but it does the job. Modifying it so it charges in 'standby' has been on my list for a few years ... I'll get there one day....!

Adrian

The users guide says:?Setting Display Intensity To adjust the intensity of the display, press and rotate the front panel knob, use the ( ) ( ) keys, or use the numerical keypad to set the intensity value between 50 and 100 percent. Lowering the intensity may prolong the life of the LCD.
Stuart K6YAZ
Los Angeles, CA

On Fri, Mar 22, 2019 at 11:45 AM, Adrian wrote:

Like I said, if you wish to retain the existing form and if you're in the USA for 8 bucks you could order a drop-in replacement NiCd pack on ebay.
Search on 'HP calculator battery'
I got three shipped to the UK about 18 months ago, one for the 8566A and one each for my ancient HP calculators. I admit they don't hold the charge as well as a brand new HP pack did back in the day, (cheap cells?) but they aren't too bad.

Plan B which also worked was:
1/ Open the existing plastic shell using scalpel along the welded seam at each end (some give in easier than others!)
2/ Cut/tear off the two contact strips off where they are welded to the old batteries and set aside.
3/ Taking a new 5xAA cell NiCd pack sold to the RC car racing community also on ebay, cut off one cell from each side leaving the welded tabs sticking out from the 3 cells you are keeping
4/ Fold the remains of those tabs such that they lie nicely with the contacts saved from step 2 and quickly solder them so stuff doesn't get too hot.
5/ Reassemble plastic case frame and drop the pack back in the 8566A's holder and clip the cover back.

Thanks everyone who replied. Is this the listing?

Sean