HP 8903A - Clean up and moving the BNC jacks to the front

[gdnichols31]

This topic is a continuation of repairing an HP8903A I have. The oscillator board was repaired. See the link below for that topic if your interested.

https://www.eevblog.com/forum/repair/hp-8903a-a5-oscillator-board-distortion/msg3327922/#msg3327922

[gdnichols31]

I started taking it apart to clean it.

First Pic
The over all shot so I can remember how to put it back together.

Second Pic
All the cards out, stacked in the order they came out.

Third Pic
Everything (almost everything anyway) disassembled and clean!

I was going to stop cleaning here and start putting it back together, but I thought It would be a good time to move the BNC connectors to the front panel. I was thinking it wouldn't take much more time.

The only problem was the input and output coaxes were run behind the plotter and monitor BNC connector board. The only way to to get the cables out was to remove the motherboard from the chasis. So much for not taking too much time! I didn't get a pic of the cables running behind the connector board, sorry.

[gdnichols31]

I was wrong I did take pic of the cables behind the board.

[gdnichols31]

Heat sink and voltage regulators removed


Motherboard removed

[gdnichols31]

Everything out except the front panel

[gdnichols31]

I got the connectors out and started re-assembly. I wanted to get it back together to make sure it still worked before I took the front panel out.

Installing the motherboard

[gdnichols31]

BNCs are gone and the motherboard is back in.

[gdnichols31]

Everything back together and it still WORKS!

Now we take the front panel out

[gdnichols31]

2 output connectors in

The input connectors in.

Ready for the circuit board

[gdnichols31]

All reassembled and on the bench ready to use!

I left out repairing the springs in the keyboard buttons. This has been covered in several other places. I do have some springs missing, but it won't affect the use of the instrument. I'll watch for a keyboard on EBay to show up.

Overall it wasn't very difficult to move them and it makes it a lot easier to use.

[wn1fju]

For the front panel leaf switches, you might also be on the lookout for a cheap (possibly broken) HP 3437A System Voltmeter.  These things often go real cheap on eBay.  Not only can you pull out the leaf springs, but at least on the 3437A's I have seen, the red plastic switch housings are not heat staked to the board.  That means you not only get a dozen or so springs, but a dozen or so switch housings should you ever need to replace one on another HP piece.

[gdnichols31]

For the front panel leaf switches, you might also be on the lookout for a cheap (possibly broken) HP 3437A System Voltmeter.  These things often go real cheap on eBay.  Not only can you pull out the leaf springs, but at least on the 3437A's I have seen, the red plastic switch housings are not heat staked to the board.  That means you not only get a dozen or so springs, but a dozen or so switch housings should you ever need to replace one on another HP piece.

Thanks, I'll set an alert for one.

[james_s]

Why not just run cables off the outputs under the bottom of the housing instead of butchering the front panel? I cringe whenever I see people drilling holes in gear.

[gdnichols31]

Why not just run cables off the outputs under the bottom of the housing instead of butchering the front panel? I cringe whenever I see people drilling holes in gear.

I considered something like that, but I don't have room for a BNC patch panel. I also didn't want an additional set of cables to add noise to the system.

Gary

[Tony_G]

Congrats again on getting this up and running. Were the original cables long enough for the swap?

As for the keyboard springs, I've heard that people have used cut down feeler gauges to replace missing springs - I think this was discussed over on the HP Groups.io forum.

TonyG

[gdnichols31]

Congrats again on getting this up and running. Were the original cables long enough for the swap?

As for the keyboard springs, I've heard that people have used cut down feeler gauges to replace missing springs - I think this was discussed over on the HP Groups.io forum.

TonyG

Thanks,

Cables are plenty long enough no problems there.  The biggest head ache was having to remove the motherboad to remove the cables at the back. Another minor irritation was the threads on the BNC connector weren't long enough for the nuts and the washers. I had to leave the washers off.

wn1fju, had a good idea above. I've got an EBay alert setup for them. Not only do you get the key parts, but you get all the other parts too!

Gary