HP 8643A Frequency Generator Won't Power Up - Page 2 - Videokarma.org TV - Video

Chris K · #16 06-15-2025, 11:48 PM

Those guys are replicating an Apollo command module? That’s insane! I’ll be getting the NOS 7624 power board tomorrow. I checked the electrolytic cap that had 140V on it Friday morning and it’s still got 40V DC stored 2 1/2 days later. I was thinking maybe the fact the transformer is screwed might have something to do with it’s inability to discharge?

bandersen · #17 06-16-2025, 09:45 AM

It's a big cap and I assume there is no load on it. It will hold a charge for a long time.

Chris K · #18 06-16-2025, 06:29 PM

New NFS40-7624 showed up today and is putting out 24V DC as it should however.....

Are these the same junk as the resin filled ones that blew out on the other board? I haven't looked at the bottom yet to see if there's a resin reservoir.

Chris K · #19 06-17-2025, 07:32 PM

It's upside down but it's working. The fan is making a god awful racket but I can take care of that. Wooo Hooo

bandersen · #20 06-17-2025, 07:39 PM

Awesome! Does it complete the calibration with no errors? Was just about to post that according to Curious Marc the 8643A schematic has been leaked and scanned

Chris K · #21 06-17-2025, 07:57 PM

Quote:

Originally Posted by bandersen

Awesome! Does it complete the calibration with no errors? Was just about to post that according to Curious Marc the 8643A schematic has been leaked and scanned

Yes I got it on a flash drive from a seller on eBay but the CLIP didn't have schematics for the 2 power boards since they are not made by HP/Agilent. Good to have them though. I did install a new NiCad 3.6V battery so yes, no wait for calibration anymore. No errors...just boots right up. Just blind luck I bought the model that has the leaked schematic. I watched the misaligned connector/blown cap and chip video from CM today. The guy has amazing diagnostic skills.

Chris K · #22 06-17-2025, 10:39 PM

Quick question Bob or anyone else who might know this, what direction is the cooling fan supposed to move air…suck air into the cabinet or blow air out of the cabinet? I’m sure someone was in here before me so I made a few assumptions as to what might have been done. The 24V fan leads plug into one of the power boards but the way the fan was bolted to the cabinet, the leads barely reached the pins and when plugged in the leads were almost under tension. I thought maybe someone might have messed with the fan orientation so I rotated it 90 degrees so the leads were much closer to where they needed to go. It made a difficult reinstall of the board a little easier. It’s probably where the fan vibration got introduced. I didn’t turn the fan around to bring air into the cabinet but now I’m thinking who knows if somebody before me had the fan out and put it in backwards? I am certain the reason the fan never ran on this machine is because the tensioned leads fell off the pins when whoever was in here before me tried to reinstall this large sheet of aluminum with circuit boards screwed to it. The clearances are minimal. Pretty long for a quick question! As for the fan…air in or out?

kvflyer · #23 06-18-2025, 06:50 AM

Every piece of equipment that I have encountered always blows the air out of the cabinet.

bandersen · #24 06-18-2025, 02:12 PM

Yes, it blows out

Chris K · #25 06-18-2025, 03:53 PM

I managed to lengthen the leads from the fan so I could reinstall it in the original position without having zero margin in lead length. The fan runs quietly now blowing out of the chassis. I posted above an image of a RIFA capacitor on the initial power board that I needed to replace with a NOS board. The cap looks different from the other RIFA safety caps that blew. Does anyone know if the cap is just as suspect and should be replaced?

Chris K · #26 06-21-2025, 08:36 PM

Put the unit back together and buttoned everything up. Turned it on and the fan powered up and then…NOTHING!!! Just a little cursor on the left side of the screen. After 2 days of seating circuit board connections over and over and checking through it with a fine toothed comb, I had one last idea. I loosened the front right side of the front panel, wedged it forward and discovered the strip lead connect from the motherboard to the front panel though still attached didn’t look right. I went in with a plastic stick and pushed it down firmly and it definitely felt like it wasn’t seated correctly. Next power up all was well. Machines continue to torture me!!!

bandersen · #27 06-30-2025, 10:24 PM

Glad you got it working. Did you see Curious Marc go inside the gold box?
https://youtu.be/buNejAFjWzw?si=1o7D4VWP0oaTaTXj

Chris K · #28 07-21-2025, 11:54 AM

Sorry I didn't see your comment/question earlier Bob. Yes I did and was awed by the level of nanotechnology in the mystery box. How in the world do they attach the gossamer thin wires to the contact points??? I also loved Ken's reverse engineering analysis of the sapphire and silicon chip in the HP 9895A controller board 8" drive reader video. The extreme magnification look at it was mind blowing.