EIP 545 Microwave Frequency Counter repair.

[Kibi]

The other day I had a chance to go for a quick rummage in the junk room and I found this EIT 545 Microwave Frequency Counter! I believe it to be of a late 1970's to early 1980's vintage. It's got a good 18GHz of bandwidth spread over three different input bands.







Now, this little find did have a "Faulty" tag affixed to it. The writing on the back of the tag was not very legible, so I gleaned no clues as to it's ailment from it.
This is one of those things that amazes me at times. Surely a person who has access to use such equipment should be fit enough to mend it, rather than just tie a faulty label to it?



Oh well, at least it gives me something to do on a lazy Saturday afternoon.
It powers up and the display works well, but it does not respond to anything on any input, just a row of zero's.
I ran "Test 01" which is supposed to display 200MHz, but alas, just a row of zero's. So then, let's have the lid off.



We are presented with a row of daughter boards, the power supply being one of them. The golden rule is that a person should check voltages first.
I probed the PSU board for a short while and discovered that the +12V rail had gone. The power supply required the removal of screws before it would come out. The other boards do not need unscrewing, so I removed each of them in turn whilst power cycling and keeping an eye on the +12V rail.
Upon power up after getting to the removal of the A107 PCB, the +12V rail came back!



Some evil tantalum capacitors immediately grabbed my attention. There were not too many capacitors on the board and I assumed that the short would be caused by a dead decoupling capacitor. I simply held one probe to PBC ground and then with the multimeter in continuity mode, I buzzed about all of the capacitors with the other probe and identified those who presented short circuits on both of their legs. Three or four capacitors presented shorts on both legs with respect to ground, but only one of them was a tantalum, so it was the first to be desoldered.
First time lucky, once this tantalum was removed, viola, the short has gone. I replaced it with another (the yellow one is the new one).



I put all the PCB's back in, powered the instrument up and the +12V is still up. Yay!

I performed a "Test 01" from both the internal and a 10MHz external reference and the expected result was returned on the display.

Internal reference.



External reference.



Wonderful!

I use an "Off Air" frequency standard which is tuned to use BBC Radio 4's highly accurate and stable 198KHz carrier.

Here I have a good lock on the 198KHz carrier.



Below are the readings I am getting from the EIP 545 with a 1MHz input on input Band 1.

Internal reference:



External reference:



Now, to test input Band 3, we need a signal greater than 1GHz. My generator goes nowhere near this, so I connected one of my higher gain (~8dBi) 5.8GHz antennas which I use for the FPV video downlink on my quadcopter directly to the Band 3 input.



My quadcopter should be transmitting at about 5645MHz.



Here I have set the counter to measure the power level at it's input. The rightmost set of digits is reading -20dBm with the aircraft placed one metre directly ahead of the receiving antenna. -20dBm is not too bad.



Well, that kept me off the streets for the afternoon. I guess I can take the tag off now.

[SeanB]

Nice repair there. Probably it was turned on, was found not working and had the tab attached to say faulty with the intention to fix later whenever. Then another counter was used, things happened and it gradually got closer and closer to the back room......

[Vgkid]

congrats on the fix, I thought I read something on that same model a while ago.
 http://bradthx.blogspot.com/2012/09/a-repair-story-eip-545a-18ghz-frequency.html

[Kibi]

Cool, that was an interesting read. He basically had the same problem as I. Excellent, another win. 

[SeanB]

Must have had a batch of capacitors that would fail in time, or they had an ESD event in storage.

[edpalmer42]

I picked up a 545A a few years ago that was a "not working, parts only" unit.  It turned out to be more like a collection of parts from different models than a proper unit.  The 200 MHz test passed, but bands 2 and 3 were dead.  It turned out that two of the internal cables were connected to the wrong jacks!  Reconnect those, retune the YIG filter and it worked fine!  So far, I've only been able to test it up to 15 GHz, but that's more than enough for what I need.

Ed

[psykok]

Hi,

I just scored a EIP 454 non A or B but without the power meter option.

Would you be able to share a dump of your EPROMs?


Alex