HP 3312A function generator

[20tajk7]

Hi, recentely chated about function generators with a friend.
So I dug out the units I have laying on the shelf and found this HP 3312A.
It powered up a fraction of second and the mains fuse has blown.



Seems like somthing has shorted, maybe a bad tatalum cap, which I guess are the yellow ones.

 

[George S.]

My father gave me a HP 5334B Universal Counter that had been sitting for years.
First time I put power to it, it smoked. There are caps in these old HP units made by RIFA. Rectangular caps in a plastic case, that cracks, and allows moisture into the cap. Power it up, and it shorts.
It's a known issue, and lots on the web about it. I ordered new RIFA caps, replaced them, and it still works perfect.
Don't know if your HP has the same issue, but it's a very common one.

 

[George S.]

Here's a photo. Two X2(big)and two Y(small) RIFA film safety caps, the rectangular ones, plastic cases.
All the plastic cases were cracked.
The yellow blob caps in the background are tantalums.
From reading about these RIFA caps, sometimes they're mounted on the power switch on HP or Phillips scopes, so they can be anywhere in the unit.
I ordered exact replacements from Mouser or Digikey. They probably sell a lot of these. The replacement Y's are now upgraded to Y2 if I remember correctly.

 

[20tajk7]

Haven't found out how to fix the focus problem on the Tektronix 464, so I left it and took the HP 3312A out of the storage.
The only schematics I've found are low res scans but the power supply is quite common +/-17VDC, a few inductors for filtering and some resistors and zeners for lower voltage lines.
Both +17V and -17V rails are shorted to ground, that's why main fuse has blown.
Started to remove the big 500µF capacitors, tested with the DER EE 5000, still good.
Traced the +17V and -17V lines, not that easy as it's double sided boards, removed some inductors and resistors, then finally found two shorted 2.2µF tantalums.
Replaced them, quick test with a 40W bulb in series as I don't have 6x32 / 160mA fuses in stock, but after a few minutes the bulb was glowing and a 10 Ohms resistor has burnt.
So I've replaced all tantalums and now it works.
Then back to storage waiting for a good restoration until I'll do a Mouser order for the fuse and a few capacitors.

 

[wattsabundant]

Haven't found out how to fix the focus problem on the Tektronix 464, so I left it and took the HP 3312A out of the storage.
The only schematics I've found are low res scans but the power supply is quite common +/-17VDC, a few inductors for filtering and some resistors and zeners for lower voltage lines.
Both +17V and -17V rails are shorted to ground, that's why main fuse has blown.
Started to remove the big 500µF capacitors, tested with the DER EE 5000, still good.
Traced the +17V and -17V lines, not that easy as it's double sided boards, removed some inductors and resistors, then finally found two shorted 2.2µF tantalums.
Replaced them, quick test with a 40W bulb in series as I don't have 6x32 / 160mA fuses in stock, but after a few minutes the bulb was glowing and a 10 Ohms resistor has burnt.
So I've replaced all tantalums and now it works.
Then back to storage waiting for a good restoration until I'll do a Mouser order for the fuse and a few capacitors.

I recently fixed a B&K function generator with shorted tantalum caps. If tantalums are more than 15 years old, seems as though there’s a good chance they shorted.

 

[mlucitt]

I have the younger brother, a HP 3311A. Mine works great, I added an LED in the front panel because the 3311A does not have a "Line" indicator like the 3312A. The best thing about this series of function generators is that they can put out 10VAC of signal.

 

[NavLinear]

This is one of the better copies I've found for the HP 3312A.

 

[philbrooksjazz]

I recently fixed a B&K function generator with shorted tantalum caps. If tantalums are more than 15 years old, seems as though there’s a good chance they shorted.

I just got one off of EBay, same problem - blowing fuses, tantalum caps visibly damaged. After replacing the caps I found the +17 regulator was bad, gets very hot after 2-3 min, no +17v. I replaced the regulator with a LM2596 DC-DC convertor, input from the output of the filter cap. Unit works correctly now.

 

[laatsch55]

Nice work..

 

[WOPL Sniffer]