IFR A-7550 Spectrum Analyzer Repair 

Yes, I coulda edit down more, but I thought it was important to demonstrate the erratic behavior over something so very simple....just incase you have one demonstrating the same issues. ~Jack, VEG

👍Nice SA and thanks for sharing. Is it possible to upgrade to modern LCD display?

Very nice find there Jack. Just a couple of observations. You can think of the tracking generator as a sweep generator. It puts out a signal that follows the sweep on the screen. So if you have it set at 100MHz center frequency with a Span of 10MHz then the tracking generator will start at 95MHz and sweep along with the screen to 105MHz. That way you can hook up an FM IF can to it, for example, and set the center frequency to 10.7MHz with a span of 1MHz. Take the output of the tracking generator to one side of the IF can and the input of the analyzer to the other side of the can and it will show you where the resonant frequency is and what the Q, or efficiency, is. Another thing, the resolution bandwidth can be a bit tricky to understand. Basically it sets how well you can see a signal. For example if you set the Resolution Bandwidth, RBW, to 1MHz and you are looking at a signal that is only 500Hz wide you won't see much more than a straight line up at the center frequency even if your span is down to 500Hz because the resolution isn't there. And one last thing, I have one of these holding down a corner of the carpet because that is all it is good for now. I had it plugged in and off when the power supply let loose and fried the unit. As mentioned before in a comment the power supplies in these are not great. For that reason I would suggest you not leave it plugged in all the time.

Jack, I would not leave those alkaline cells in there as they will leak. Get a coin cell battery holder for a CR2330 or a 2450 (you have plenty of room) insulate the bottom of it so you won't have shorts. The proper sequence after changing the battery (or updating the EPROMS) is to pull the SRAM to clear the bogus data, reinsert the SRAM. Install the CPU card and then cycle the power 3 times on the 3rd power up use the keypad and run the RF attenuator up and down a few times. This initializes the SRAM. Power the unit down then up. After that sequence the unit will function normally. On power up to save time after that as soon as you see the splash screen you can press any key to cancel the splash screen and start using the instrument. Sam W3OHM P.S. in my case I did not have a holder handy so I made a battery assembly using a CR2450 I had. I soldered wires to copper tabs and then used anisotropic Z axis conductive tape to bond the copper tabs to the cell and then enclosed the cell in some low temp heat shrink. I soldered the wires to the CPU board and then tacked the cell assembly in place with hot melt glue. With the capacity of the CR2450 it should be good for another 30+ years!

Looks to me like you fingered it out Jack. Congrats. Now just find the correct battery and you will be golden. I'm not built that way, I can't just use any old battery, I have to have the correct one. Kudos to Mrs. VEG for all her help. To paraphrase something I heard a lot when attending electronics tech school was the problem with most test equipment is that it will give you some sort of reading or indication. It's up to the individual to figure out what it means. In other words, those readings or indications are open to the interpretation of the person doing the testing. :)

have a simular problem with the old Packard Bell i486 PC, the bios is mandatory. It's stupid that they solder the bios battery on the PCB.

Jack, Never disconnect cables while the unit is powered on. I have repaired one of these before . They are useful instruments. The power supply is a poor design by today's standards, as are many early . switchers. You will probably find many leaky caps in the inverter. Be careful soldering on these IFR blue circuit boards. They don't tolerate heat well and tend to lift traces. Good luck.

um totally clueless, never used one.