Ok see my post to another group about this issue.
Re: IFR 3414 Signal Generator Repair (spurious signals on output)
Michael K.
Jun 12
Hi Gents,
I have four or five different manuals/data sheets on these supplies. One manual states that it needs a fan even if the PSU is On but there is 0 load (when using the enable control of the PSU via the molex connector).Always thought that was strange so I dis-regarded it just to have it bite me in the rear, let me explain.
My first 3413 five years ago had a PSU that had the SMD resistors under L12 burned, actually the PCB was burned very badly due to those resistors heating up (90 - 100C). This location is at the edge of the PSU that faces the fan. But at the time I thought that the supply just burned up due to a bad fan, I’m sure that did not help things. Since I did not have any schematics I purchased another supply that had basically the same PCB as mine. This allowed me to do a few resistance measurements of a known good unit. Even though the PCB was burned I found an open trace in this area. Fixed the trace and also replaced all of those SMDs. Turned the unit ON and it worked. Put it back together and put it back into the rack. Plugged it in and left it on standby to keep the 10mhz oven on. After a few months I noticed this smell, did not really know where it was coming from. Until it became so bad I had to track it down. Well it was the PSU again at that location. This time I replaced the entire supply with a new one, known good. It turns out the new one was also getting hot at the same location, strange. I verified this temperature on my other working 3416, same temp. Another printing of the manual does not mention that cooling is required at 0 load. On the 3413 the fan pulls air through the PSU but on the fan versions of the PSU (EM and TM) the fans blow in onto the PSU as soon as AC is applied (when the enable molex is used) to the PSU (Let’s say as soon as you turn the rear switch on to the 3413, fans would be running to cool this area down).In the 3413 even though it gets AC power as soon as you turn the rear switch On there is no fan that turns On until you push the button on the front panel. These supplies are slowly baking when in standby mode. Look at your PSUs I’m sure that the location is discolored at best.
On top of this you guys are also seeing temperature issues as well. I can understand some of the over temperature signs are coming from environments that are warmer than your typical electronics lab, We don’t have AC running all of the time. This would mean that the temperature mitigation is marginal.
If your unit is in a warm room don’t leave it on standby turn it off.
Another way that might work to cool it down while in standby is to take the fan leads that cool the PSU and plug them into the PSU fan terminals. The fan would turn On as soon as the rear switch to the 3413 is turned On. This PSU fan output runs the fan at the same speed as the 3413, slow with very little noise. When the PSU gets warm it will speed the fan up like the 3413 fan control. Not sure if the 3413 might sense a disconnected fan.
Well hope this helps to shed light onto the marginal heat mitigation of this unit.
Last comments would be on finding good CSF250 supplies that would be a fix for any bad original supply. If you have a bad supply that can’t be fixed, don’t throw because you will need the transformer out of it.
Michael
Ok this is what I posted yesterday.
I have two 3416 and one 3413, all have the same heating issue.
Your thoughts?