HP 8904A Options - Page 1
Forum section: electronics / testgear

author: davorin
author_rank: Unknown
timestamp: June 08, 2014, 01:46:09 pm
content: HelloI just received an old HP8904A signal generator with no options installed...Is there a way to still get the options keys for the software options?

author: PedroDaGr8
author_rank: Super Contributor
timestamp: June 08, 2014, 02:14:57 pm
content: With that generation the options may actually be hardware modules that get installed. Not sure because it's appearance is right on the border between actual hardware options abd software key based options.

author: davorin
author_rank: Unknown
timestamp: June 08, 2014, 02:18:34 pm
content: Well...currently no need for options...as the device went up in smoke with just being plugged in, but not powered up...From my experience it must be burned resistor(s) (o;

author: max666
author_rank: Frequent Contributor
timestamp: June 08, 2014, 02:29:15 pm
content: Just out of curiosity; you did check if the voltage select switch is in the 230 V position, right?Options:001 Adds three more identical internal synthesizers (channels) which either can modulate the first synthesizer or be summed to the output002 Adds second internal synthesizer and output003 Adds fast hop and digital modulation004 Connectors on rear panel only (not available with Option 005 or 006)005 Adds unit to unit phase synchronization006 Changes output 1 from a 50 Ohm output to a transformer-coupled, 600 Ohm balanced output61024 Rack-mount Kit for a single HP 8904A61025 Rack-mount Kit for mounting two 8904A's side by sidepretty sure those options require hardware changes, does the 8904A have software options?

author: davorin
author_rank: Unknown
timestamp: June 08, 2014, 02:39:19 pm
content: Yes..it is switched to 230V AC as it was used before in Germany...Sadly the service manual only contains some analog section...no power supply schematics..

author: wn1fju
author_rank: Frequent Contributor
timestamp: June 08, 2014, 02:42:43 pm
content: In case you are able to fix the 8904A, there is a way to enable all of the software options. You will need to familiarize yourself with HP Service Note 8904A-05 which shows how to recover from a general battery backup failure. Then there is a method to write a specific address with a value that will enable everything, namely 0xFF into address 3FFC. This procedure is documented in a series of e-mails which I'm looking right at now (I stuck them in my manual years ago). If I remember, they were freely available on-line, perhaps in the Yahoo HP group. In a pinch, I guess I could mail you a copy. With no extra hardware options, at least this procedure gives access to the multiple channel option (001), which is the biggest bonus.

author: davorin
author_rank: Unknown
timestamp: June 08, 2014, 03:12:24 pm
content: First I need to open the covers...Got it open now...and see now some black, sticky stuff just below the line filter from the AC line...

author: SeanB
author_rank: Super Contributor
timestamp: June 08, 2014, 03:42:33 pm
content: Ah, the Schaeffner curse yet again. Likely that is the only fault there. Plenty of discussion on those accursed filters around here.

author: davorin
author_rank: Unknown
timestamp: June 08, 2014, 03:51:58 pm
content: Yes...you're right :-))Found this on another forum...Think test-wise I just mount a regular AC plug without filter as it did once powered up successfully...

author: Richard Head
author_rank: Frequent Contributor
timestamp: June 08, 2014, 06:33:03 pm
content: Yip. Happened with me too, on two occasions.Plugged in my new instrument and after 10 minutes smoke.I had it happen to two different instruments.Luckily I was able to get an exact match from RS, albeit at a price!

author: davorin
author_rank: Unknown
timestamp: June 08, 2014, 07:37:54 pm
content: Is there a document about the commands used in the HP Service Note 8904A-05?Like how to write 0xff into location 0x3ffc?

author: wn1fju
author_rank: Frequent Contributor
timestamp: June 08, 2014, 10:21:26 pm
content: I found the service note at:http://exodus.poly.edu/~kurt/manuals/manuals/HP%20Agilent/HP%208904A%20Service%20Notes%202.pdfOr simply google "HP 8905A-05 Service Note".Basically, what you want to do is follow the procedure as if you were going to change the three addresses at 3FFD, 3FFE and 3FFF, except you don't want to change those three - you want to use the up/down arrows to get to address 3FFC and then enter in FF for the data at that address.You may have to fumble around or try a few times as I'm recalling all of this from years ago. But I was ultimately successful and enabled Options 001/003/005. Have fun.

author: davorin
author_rank: Unknown
timestamp: June 08, 2014, 10:28:21 pm
content: Well..with the up/down keys it was clear to me...but not how to enter the hex code...So you say I can just move to 0x3ffc and try several times until I'm lucky and not mess up to end up with a dead device?

author: davorin
author_rank: Unknown
timestamp: June 11, 2014, 02:43:17 pm
content: Today a replacement ac inlet/filter arrived today...not a perfect match as it is larger but I made it fit by bending the pins (o;Used a Schaffner FN9222B-3-06 now as it was the closest model available here in Switzerland.Now for the option hacking (o;

author: davorin
author_rank: Unknown
timestamp: June 11, 2014, 03:19:37 pm
content: Wow...that was easy :-))At the step where the technical note says "NEXT, NEXT, NEXT, f1, 4, 0, 0, 0"then you actually set the start address...you could just press 3FFC....to switch over to enter the data itself...just press "f2" (it actually shows you on the display ;o) and then press twice "F"...then exit with twice "f4", power cycle the bastard et voila...options 01/03/05 are displayed :-))Code:Power-Cycle/Power-OnSHIFT, SERVICE, SHIFT, f4, 0, 9, 2, 4, 4, 8, SHIFT, SERVICENEXT, NEXT, NEXT, f1, 3, F, F, Cf2, F, F, f4, f4Power-Cycle

author: TheDefpom
author_rank: Frequent Contributor
timestamp: March 20, 2017, 07:09:41 am
content: I purchased one of these recently to fix it in a video for my channel.It has a dead power supply, and whilst trying to trace the fault yesterday the filter blew up in front of me, I was actually recording a video for my channel at the time, so I caught it on camera !I think I traced the dead power supply to Q4 being blown, an MJE18006, it is completely shorted out, so I am hoping that is all that is wrong with it (apart from the filter of course, I wonder if they were not really designed for 240V operation?), I wasn't able to find a proper circuit diagram for it either.I will be posting a video to my youtube channel after I have finished piecing together the video sections, in case anyone wants to see the filter blowing out and the smoke.... it stank, my lab still smells badly from it today !Video will be here (once it has finished uploading and processing... will be a multipart due to the need to get parts in):

author: SeanB
author_rank: Super Contributor
timestamp: March 20, 2017, 04:16:42 pm
content: Whatever drove that transistor is guaranteed fried, along with the emitter current sense resistor, the base resistor if there and of course the blown fuse. Bridge rectifier might also be blown. Replace them and the small electrolytic capacitors around the controller chip as well, and check the snubber resistor capacitor and diode is still intact.Then run the PSU unloaded with a dim bulb tester, and see if it at least tries to start up and does not light the bulb to full brightness. May or may not run properly with no load, but should have some life on the secondary side.

author: douardda
author_rank: Regular Contributor
timestamp: March 20, 2017, 05:03:26 pm
content: I did a blog post on my HP 8904A PSU problem and repair. It's most probably not very useful for you since the pb looks very different, but just in case. I did reverse eng. a part of the schematic.https://whatever.sdfa3.org/tag/hp8904a.htmlDavidEnvoyé de mon GT-N7105 en utilisant Tapatalk

author: TheDefpom
author_rank: Frequent Contributor
timestamp: March 20, 2017, 05:27:34 pm
content: I did find that blog when I was searching for info, a very interesting and helpful page, yours had a different fault to mine, but the power supply is the same one, I have saved the diagram to my records as I expect it will be needed, one thing I did notice is the ic numbers, mine are not lm393 but lm392.

author: TheDefpom
author_rank: Frequent Contributor
timestamp: March 31, 2017, 06:22:37 am
content: I did some more investigation about the options once I repaired the unit I have here, I figured out the codes required for each option, and how to set it correctly, instead of using "FF" which results in trailing slashes due to invalid option selections (non existent options).I did a video on my channel for this, showing what I found and demonstrating how to set the options.

author: primetechie
author_rank: Newbie
timestamp: May 10, 2022, 04:54:44 pm
content: I have an 8904a with Option 2 installed but following the process in this thread I cannot add options 1 or 3.Option5 always adds but options 1 and 3 never do.Is there another address that needs to be modded in order to have this work on some firmware? I am showing Firmware 152888A on mine.Placing 07 at EFFC gives me options 2/ / /5; while placing FF gives me the same but with more empty slashes to the rightAny suggestions would be gratefully appreciated.Thanks

author: TheDefpom
author_rank: Frequent Contributor
timestamp: May 10, 2022, 11:25:58 pm
content: I believe option 1 is a hardware option, and without it you also won’t get option 3.

author: srb1954
author_rank: Super Contributor
timestamp: May 11, 2022, 04:43:10 am
content: Quote from: max666 on June 08, 2014, 02:29:15 pmI think options 001 and 003 were software enabled. Options 002, 004, 005 and 006 require hardware modifications.

author: primetechie
author_rank: Newbie
timestamp: May 11, 2022, 11:19:32 pm
content: Scott - you may be right. I found another one with option 1 installed and was able to add 3 and 5 to it. So it seems that Option1 may in fact be a hardware option and without it. you cannot add 3. If you have the HO8 option that either IS Option5 or allows it to be added.The 8904A I was 'complaining" about has options 2 and HO8 installed and has a faulty ROM <AHAH!> that does not keep settings after a power cycle - so that may need to be addressed. 123 (Battery is good and tested and feeding a 3V 25ma current from a PS to the battery points doesn't fix the issue - so the current is there ) I'm hacking my way through this without damaging the units. New ROM chips may be in order.Not overly familiar with these (yet!) so any advice will be listened to.Except moving to OZ- I'm already sold but my owner is less enthralled.

author: yyudin
author_rank: Newbie
timestamp: November 14, 2022, 07:43:50 pm
content: Quote from: TheDefpom on May 10, 2022, 11:25:58 pmI have an 8904A that came with only Option 2 factory-enabled. By entering the value of "07" I was able to enable Options 1 and 3. So this is definitely feasible!