Ok, back home with unit now. Let's see what we are dealing with..
![](http://doc.xdevs.com/doc/HP_Agilent_Keysight/3458A/img/face_1.jpg)
![](http://doc.xdevs.com/doc/HP_Agilent_Keysight/3458A/img/bottom_1.jpg)
![](http://doc.xdevs.com/doc/HP_Agilent_Keysight/3458A/img/side_1.jpg)
![](http://doc.xdevs.com/doc/HP_Agilent_Keysight/3458A/img/back_1.jpg)
Steel chassis is rusty on rear side. Not nice treatment for such an instrument.
![Sad :(](https://www.eevblog.com/forum/Smileys/default/sad.gif)
![](http://doc.xdevs.com/doc/HP_Agilent_Keysight/3458A/img/open_1.jpg)
![](http://doc.xdevs.com/doc/HP_Agilent_Keysight/3458A/img/rusty_1.jpg)
Removing covers...
![](http://doc.xdevs.com/doc/HP_Agilent_Keysight/3458A/img/dirty_1.jpg)
![](http://doc.xdevs.com/doc/HP_Agilent_Keysight/3458A/img/dca_1.jpg)
All analog stuff is contained in aluminum box, isolated from steel frame by plastic inserts. HP calls those boards inside as "inguard", rest boards are "outguard".
![](http://doc.xdevs.com/doc/HP_Agilent_Keysight/3458A/img/open1_1.jpg)
![](http://doc.xdevs.com/doc/HP_Agilent_Keysight/3458A/img/open2_1.jpg)
View on both sides without covers. As we can see, no A9 voltage reference present
![Banging Head |O](https://www.eevblog.com/forum/Smileys/default/bangheadonwall.gif)
![](http://doc.xdevs.com/doc/HP_Agilent_Keysight/3458A/img/top_open_1.jpg)
![](http://doc.xdevs.com/doc/HP_Agilent_Keysight/3458A/img/bot_open_1.jpg)
Inguard PSU. Some PCB damage around CR12 visible.
![](http://doc.xdevs.com/doc/HP_Agilent_Keysight/3458A/img/ingrd_psu_bot_1.jpg)
![](http://doc.xdevs.com/doc/HP_Agilent_Keysight/3458A/img/ingrd_psu_top_1.jpg)
Outguard primary PSU. All seems ok.
![](http://doc.xdevs.com/doc/HP_Agilent_Keysight/3458A/img/outg_psu_bot_1.jpg)
![](http://doc.xdevs.com/doc/HP_Agilent_Keysight/3458A/img/outg_psu_top_1.jpg)
68000 CPU, RAM, ROM and digital logic, board A5. Dated 1990, while rest of analog PCBs dated 1996.
Probably seller changed digital PCB afterwards?
![](http://doc.xdevs.com/doc/HP_Agilent_Keysight/3458A/img/a5_bot_1.jpg)
![](http://doc.xdevs.com/doc/HP_Agilent_Keysight/3458A/img/a5_top_1.jpg)
Removing inguard PSU for now, adding jumpwire instead of fuse (don't have suitable cap), turning on...
![](http://doc.xdevs.com/doc/HP_Agilent_Keysight/3458A/img/digital_only_1.jpg)
Aha. Nice and bright VFD, which is cool. Now will remove Dallas NVRAMs , and solder sockets instead, so we can troubleshoot this RAM 1 LOW.