Products > Test Equipment
HP 8116A More Help Needed
Mick B:
--- Quote from: pqass on July 30, 2023, 04:29:43 am ---First of all, I don't own an 8116A.
However, looking at the schematics, I see that the LEDs and 7-seg. display are controlled by two 74LS374s and ICM7218A (U24, U23, U22 on page 3C). If I saw LEDs stuck-on, I would check if the CPU (U1 on page 3A) was reset and is running properly; seeing if the logic power rail is 5V, that there is activity on the address pins (pins 9..25 for A0..A15) and clock (pin 37 for E) being 1/4th of 4Mhz (I think).
--- End quote ---
Pqass, Thank you for responding, you have no idea how grateful I am to have you and others take an interest in my problem. After removing all 6 Shaper output amp power transistors, and confirming I had both 24v rails, I hooked up all 4 outputs of U7 to my scope. and all 4 did exactly what they were supposed to, no PDD. I reassembled it and turned it on, it performed the LED/Switch check and then "Displayed E-41" as expected.
I was ecstatic. I'm thinking maybe because when there is a current draw on R35 or R36 it kills the 24v regulators but all the other voltage are still present keeping U1 in a constant state of shut this thing down. and sending a continuous PDD signal instead of a 1ms pulse, keeping the reset signal from being enabled in U27 locking everything up. this only a guess as I am a noob, and I'm sure there is a more logical explanation,for this madness.
Now I need to come up with some heatsinks for the power transistors on i'm dead in the water.
Mick B:
I was going to say I have hour's but it's days into this HP8116A, I have got it to the point of "E41" which is to be expected, I have removed all 6 power transistors, if someone knows how to remove the heatsinks without breaking them, :palm: please tell me. Hopefully someone bought one of these FG's for parts. I also posted this in the sell & buy forum here.
-$ I'm in need of the heatsinks from an HP piece of HP test equipment or anything that has a heatsink like the picture. Thanks.
MarkL:
You can search around for "TO5 heatsink" and try to locate something usable.
It looks like a direct replacement would be Wakefield 260-4TH5B, which has a BeO (beryllium oxide) insulator. They are not readily available due to the high toxicity of BeO, but you could probably substitute 260-4TH5E, which is the epoxy insulated version.
Mouser has the latter in stock, but you're not going to like the price at $26/ea.
There's a listing on ebay for the studded epoxy version, if it will fit in the 8116A. Or maybe you can remove the stud and drill and tap it to fit like the original. $5/ea.
https://www.ebay.com/itm/372640777684
You didn't say what broke on the original, but I'm guessing one of the sides separated from the BeO ring. I've had this happen on several of these style heatsinks (on a Tek FG504) and I just reattached the two pieces with thermal epoxy. Don't break or grind the BeO ring. It's a hazmat; read up on it.
factory:
The same heatsink is also used in the 8112A pulse gen, it's listed as "260-4TH5B-special thread", the manual fails to give any warning about BeO, some older oscilloscopes from Tek & HP also use BeO insulators.
It shouldn't be hard to find a dead 8112/8116 for parts, the hybrids are often missing or faulty.
David
Wallace Gasiewicz:
I ran into a similar problem with a TO 5 power transistor in a DC to DC converter in a military radio. The part was an unobtanium TO5. I substituted a TO 66. I had to cut off the "ears" however. The transistors in a TO 5 package are also made in TO66 packages with identical characteristics but higher dissipation. I think this is because of the better heat sinking. The transistors have different numbers though. I did this because I fortunately found a bag full of the flanged transistors at the radio shop. I have quite a few.
I am writing this in the hope that you may be able to mount the TO 66 package, The "ears" do require some extra room. In my application I could not fit them into the spot. Also the "ears" could not touch because of their polarity.
If you can mount a flanged transistor, it will probably dissipate the heat more readily.
I hope I got the numbers of the TO packages correct.
I recently repaired two HP 8165 "signal source" I do not think it was worth my time.
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