HP 8904A Restoration and Lab Checkin

[@davidv1289]

Nice unit! I use one to modulate an HP 8657B for FM tuner alignment - works perfectly. As others have suggested, you should consider replacing the Rifa caps in the SMPS. Also, all software options can be easily turned on, info is available on the web and uses the programming info in the dead battery recovery service note. The display uses an ELP and many of these units have dim displays. Fortunately it uses a standard 2-line LCD display and one with an LED backlight will fit - I seem to remember it needing some different standoffs. I added a small interface board with a pot for backlight brightness control. Regards, David

[@solodolo6018]

Love the vids Zen! I've been learning a lot from you

[@apollorobb]

I have a Kenwood SG-5150 nice to have a dedicated Stereo generator but i do tuners all the time . Didnt know the 8904 had all those goodies .

[@szapcsika]

Sync out in is an option when you can connect several of these units so all of their output is in phase. Can be useful. It is a software option but of course you need the bnc connectors.

[@Wil_Bloodworth]

Great to know!

[@andywlala]

You gonna swap out those three RIFAs too ? Being a 110V country probably not real high priority, but since you had it open …

[@Wil_Bloodworth]

Thank you. I just bought this very same model with the same options. Can you please tell me which capacitor series you used and which series you chose for the low-ESR capacitor. Much appreciated sir!

[@roymercer6967]

Why are the four outputs required? This is the first I have heard that the four outputs are required. Thank you for another well done video.

[@ZenwizardStudios]

The 4 outputs are for the floating option. Like a SMU when the output is set to floating there is Signal high and Signal Low. I might have mentioned this is for differential signaling but that is NOT the case with this unit. There is another video on the way that will go a bit deeper in to this.

[@roymercer6967]

I should have paid closer attention. Thanks so much for taking the time and responding.

[@vk5fe943]

Nice video, thanks. Apparently the AutoDigits in the 53230A setting is Off - if so, probably all the digits after the nineth or tenth digit after the decimal point is just garbage.

[@ZenwizardStudios]

I will check on the auto digits. I have the 53230A set up for testing some 10 Mhz lab references (videos will be out shortly) if the gate time is not long enough things will bounce around but the 53230A only needs a gate time of about 0.1 Sec to settle down quite a bit.

[@stephenbell9257]

That battery also backs up configuration info like serial number, S/W option keys etc. If the battery goes flat you will lose these and it is quite difficult to restore them.

[@ZenwizardStudios]

The S/W Option key is very easy to restore. I need to look in to the serial number what that entails.

[@szapcsika]

@@ZenwizardStudios Search for HP Service Note 8904A-05. It details how to recover from battery loss by entering some magic parameters. After that you can use the service manual to reenter the serial no, and the options.

[@ZenwizardStudios]

Do you by any chance have a PDF of the complete service manual? Most of what I am finding on line is missing section 4 which is the alignment procedure. I do have that service note but I also need the complete service manual. Would like to do a full alignment after I get the appropriate power meters. I will need those for my spectrum analyzers as well.

[@JohnInnocentSmyth]

hey, how is the sound quality in a stereo modulated signal? I am asking because i can see it's frequency limit is 600khz. Normally, for voice you would need larger frequency range? Maybe 1khz to 12khz? Or am i wrong?

[@ZenwizardStudios]

1Khz to 12 Khz is well within the 600 Khz range of an 8904 however this is only the data content of the FM signal. You need to feed the 8904 in to an 8656, 8657, 8642 Or other some such instrument with a external modulation input to get the RF carrier that is needed so a receiver can be tuned. The 8904 also does not to audio in to the RF source it is pure tone based. But is could theoretically be set up with some difficulty to produce some audio but an RF generator would still also be needed.

[@brianst.pierre6566]

Careful with the battery. If it dies I’ve heard the unit can be bricked. Also, see Defpom’s video on how to turn on all the software options.

[@szapcsika]

There is a service note from HP on how to reconfigure it if the battery goes flat. So battery replacement is not an issue.