The repair of an HP3562A...

[Turbon]

Hi. I'm glad you found this post , You might be able to help me  .

I got me one of these today and at a first test - the display was blank. In to the trunk with it and drow it home, fired it up... I got things on the display. The tests passed - out of focus though and needs some alignment as the picture is tilted on the screen - but it works... Or more like it - worked. I tried to focus and allign with the controls at the rear and after that - no picture . Opened it up and took some pictures of the internals without disturbing anything. Looked over the top display board to find that it is loose - no screews?! Thought I smelled heat so I turned it off and put everything back again. I have to consult the drawings from now but surely the display board should be fastened to the display unit? I'll see if I can attach photos describing my journey.

Regards

[Turbon]

Hi again.

I'm looking at figure 6-1 in the hp1345a manual. As I understand there should be 6 H5 screews and 6 MP10 washers fastening the A1 board to the display enclosure. Probably they serve as groundpoints as well. U30 might need isolation. I haven't found that information yet. Sorry to say I only printed some parts of the manual . Does someone know what sizes, materials these parts consists of?

I've started to think tearing it to parts to be asured of that none of the missing screews doesn't roll around on the main board. At the same time everything dodgy could be replaced as old caps, darkened resistors together with a general clean up of boards and connectors.

Addendum: the feet are missing that supposedly would fit into the 4 corners at the bottom of the unit. The rear feet are missing. Maybe some screews and plates are missing at the front of the analyser. Probably due to that the previous user found use elsewhere for the rackhandles or thought they have a value at the ePay... Who knows. Well I can live and use the instrument without those parts. Surely thought every hole will eventually get the right size torx.

Regards

[Turbon]

Addendum 2.

I took it apart to pieces last night so it became late/early depending on how one sees it.
At many places I noticed that the wrong screews had been used. Apart from that I couldn't find any obvious problems. So it is now in one piece again. The next step is to start measuring to get the display working reliably. Right now it has no picture but I can get a bright dot showing up on the display if I quickly turn the align pot at the rear.

Regards

[Turbon]

Measured the voltages from the main psu, seem to be near whats expected. Found an 1A fuse inside the 1345A looking suspicious and indeed it was open . Measured the rest of them and they seem to work. Will buy some replacements tomorrow. Fingers crossed, hopefully it died out of old age .

[Turbon]

Now this thread belongs in the Repair section. Can I move it by myself or do I need assistance from the admins?
Thank you admins .

Regards

[wn1fju]

I have fixed several HP 1345A displays and they all suffered from exactly the same problem:  shorted (2.2 uF if I remember) tantalums.  Disconnect everything from the display and put an ohmmeter across the 15V rail to ground.  If shorted, start lifting one side of the various caps until you find the problem.  Do the same thing for the -15V rail and the 5V rail.  Or, alternatively, use your favorite technique for finding shorted caps on a power rail.

[Turbon]

Thanks a lot wn1fju! I will check it when I feel better if the prblem prevails. I thought I solved it by disconnect everything and reconnect. It showed to be that when I disturbed the 1345a the fuse engaged and suddenly everything worked until I disturbed it again. So, eventually when I get hold of a new fuse and if it blows I will check your tip. But it won't happen today at least...

Thanks and regards

[Turbon]

Right, fuse replaced and suitable screews installed. Nylon insulators used on the two TO-220 devices on the A1 board. Everything seems to work for now. In the coming weeks I will check the main psu voltages a bit closer regarding ripple levels. Another annoying thing is the buttons - they feel sticky. It takes a bit to much force before they let themselves be pushed in. Maybe some earlier owner poured Coke over them ;(

Regards

[dom0]

If this machine has the olde 70s/80s 'hard' (not rubbery-like) push-buttons... well... they just do that. Cleaning helps somewhat.

[Turbon]

Thanks dom0. Indeed the buttons are of the hard type. How should I clean them? Is it between the buttons and the front panel or in the actual switches?

Regards

[Turbon]

Another question. I don't know if these are actual errors in the machinery or if the operator is to blame  ...

The first picture is of an external 1khz 10mV sinus. Where do the trailing negative spikes come from? They are actually appearing randomly.
The second one shows an internal 2khz sinus signal. Suddenly I got these trailing positive spikes dancing around.