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8904A display
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I posted how I put in a new display in the files section a while back:
/g/HP-Agilent-Keysight-equipment/files/8000%20to%209999/8904A%20%20Multifunction%20Synthesizer%20%20Notes/8904A%20display%20mods.pdf The extra thickness of the led backlight does require spacing the shield back, so the pem nuts in the top of the shield don't line up with the screw holes in the top of the front panel.? I felt that was acceptable and it has not been a problem on my units. If you have any questions I would be happy to help. -Mac |
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Mac, Thank you for pointing out this information from the files. I only opened the case once for the adjustments, so I don't have good "memory?photography" on the bits in there, but the part on p.4 of your document exists in the unit as is, or is a new part that needs to be purchased? It looks like the adjustment pot (which looks like maybe a 1/4" Bourns pot?) is attached directly to it,?and one pin gets trimmed from original?HP part of newly purchased part, whichever it is.? Thank you, Radu.? On Mon, Mar 7, 2022 at 1:18 PM Mac Perkins <macp@...> wrote: I posted how I put in a new display in the files section a while back: |
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Mac, Scratch that, I think those two 14 pin DIP (?) machined sockets are what I was looking at. Right?? Radu.? On Tue, Mar 8, 2022 at 12:16 AM Radu Bogdan Dicher via <vondicher=[email protected]> wrote:
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¿ªÔÆÌåÓýHi Radu, Yes, that assembly is just two machined pin sockets stacked as an easy way to intercept the wire on pin 2 of the DIP cable from the display, which is the contrast adjustment on the new display I used.? The pot supplies an adjustable positive voltage to the contrast input on the display.? I seem to remember the original display used an opposite polarity contrast adjustment, this was an easy non-destructive workaround. ?The supply that feeds the EL HV inverter module puts out enough current to happily drive the LED backlight and by using it the backlight dimming and timeout still work. Some of these units have option 6, an output transformer.? Interestingly, if option 1 is enabled on those units it is possible to put DC on the primary of the transformer which can produce interesting distortions. Also, the option 6 transformer¡¯s turns ratio is such that the output voltage setting, normally P-P volts, is now RMS volts.? That had me scratching my head for a while until I read the fine print in the calibration section.? -Mac |
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Mac, I'm getting ready for surgery on this and have a question or maybe two for you. Thank you very much in advance.? How the stacked DIP sockets work seems pretty straight forward. I may just try to resin-glue the pot sideways, to allow for adjustment from the back of the unit, as it has the lid off. I think the way you did it, it may require a very short tool to perform the adjustment. Or a bit of a slant of the tool as it goes in, so to speak, and a long reach tool at that. Probably not a big deal, will assess if really necessary as I dive in.? Now, the ribbon display cable - did you transplant it from the old display? If yes, is it an easy 1:1 job? I haven't taken it apart enough to see that far yet, but I'm wondering if the way to re-solder the ribbon cable is pretty straight?forward on the replacement crystalfontz unit. Thank you, Radu.? On Wed, Mar 9, 2022 at 5:05 PM Mac Perkins <macp@...> wrote:
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¿ªÔÆÌåÓýI did the 8904 display modification in 2016, so it is not fresh in my memory. I don¡¯t remember the contrast adjustment being particularly difficult, although the adjustment is on the side of the stacked dip connectors, which plug into the main processor board behind the front panel board, so your comment makes sense. As you suggest, if the adjustment access was in the plane of the socket, then it would be a top access which would be easier. The ribbon cable assembly is the original one, I just desoldered it from the original display and soldered it into the new display which conveniently has the same interface footprint. No modification is needed, the dip socket assembly takes care of the different contrast adjustment scheme for the new display. Cheers, -Mac |
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Mac, Thank you for responding. It seems that the newer units - such as the?one you recommended on the document in the forum files (at least in its current iteration) - come with 16, as opposed to the original 14 pins. I can't find good data on the utilization?of the pins in the original LCD unit that came with the instrument (so I'd try to map one-to-one the pins). Ideally, offsetting?the 14 pins of the original?ribbon would match the new unit's 16 pins - something like ignoring pins 15, 16?? Currently researching this.? Radu.? On Sun, Apr 10, 2022 at 7:55 PM Mac Perkins <macp@...> wrote:
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