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Help with 2712 Spectrum Analiser


Marcus - PP5MS
 

Hello!

My name is Marcus and I am from Brazil.
.
I just received a Tektronix 2712 that I wanted for a long time. I bought it at a local auction and I already expected it to have some problem.
Visually it's very good, so I turned on the power to see how it works.
I was very happy to see the apparently normal screen.
However, I noticed some problems.
I set the clock / calendar that was totally wrong as expected, but by turning the power off and on, the settings are lost.
I already read on the internet that there is a battery to be replaced, which I intend to do soon.
But unfortunately there are more problems.
Although the scan line appears on the screen, even with the characteristic noise of spectrum analyzers, it does not show any signal.
I turned on the 100MHz calibrator. and it doesn't appear either.
The frequency meter does not show any reading and the following messages appear on the screen on the left, below the configured parameters, that is, in the fourth and fifth line:

UNCAL
CANNOT COUNT (VCO, IF)

In the "FREQUENCY COUNTER TEST" screen I have the following information:

0 VCO, LOCKED
1 BEAT, LOCKED
2 VCO, NOT LOCKED
3 BEAT, NOT LOCKED

Could someone point me on the right direction to look for the problem?
Any help will be very welcome, I wanted to put my Christmas gift to work ...!

I wish a Merry Christmas to everyone !!

Marcus - PP5MS


Jean-Paul
 

Marcus,

1/ get service manual for your serial numbers, Tekwiki, BAMA archive, for free pdf, or Artech, Qservice for pdf, cd or printed version, perhaps 10-50$

2/ open unit, find and replace battery, inspect for leaking SMD lytics, bad PSU caps, shorted tants, overheating parts

3/ input mixers are susceptible to overloading, symptoms no response only noise.

Bon Chance

Jon


Jean-Paul
 

Of course check power supply voltages first and use debugging flowcharts in manual

j


WB6GHK
 

Hi Marcus,

The Tektronix 2712 spectrum analyzer is a very good unit and it is definitely worth your time to fix and keep. The 2712 is part of a family of compact spectrum analyzers (2710/11, 2714/15) made by Tektronix. There are service manuals readily available and collecting and reading them will give you good understanding of the units. The biggest issue will be BOTH troubleshooting and the cost of replacement parts. While all of the other suggestions provided will get you going in the right direction, I suggest you look for a failure of the following items in this order:

1. Intra-board cabling may not be correct, use the service manual to confirm cable routing. I believe the first page of schematics in the 2712 service manual has a drawing of the modules and the cabling. It is not uncommon for techs to troubleshoot a unit and then when they find it is not economical to repair they just hurriedly put the unit back together and it goes to scrap. Sometimes cable aren't connected, may be damaged (bent pins), missing, or connected to the wrong port or board.

2. The A21 100 MHz oscillator board may not be putting out the 100 MHz frequency needed by the 2712's subsystems, reflected in the error messages you posted. With a scope or frequency counter, check J110 (level unknown), and J130 / J140 (about -4 dBm for either) for frequency and output level. If there is no signal, or it is weak or distorted (check by 100 MHz or higher input scope), then you will need to replace the assembly or component level troubleshoot the board.

3. The A18 Input Attenuator module has the front panel input and the internal calibrator signal fed through a TO-5 can relay used as a switch into the first attenuation stage. Try cycling through the front panel Level steps to see if an input signal is displayed at any point. There are five attenuators where one of them could be damaged from an excessive input signal, typically from an accidental connection to a transmitter. Worse case is you can bypass the attenuator, or connect the calibrator signal directly to the RF Mixer low pass filter input for testing.

4. The A16 RF Mixer has internal and difficult to replace mixer diodes that can be easily damaged by a high level signal. If the attenuator is set to zero dBm attention, a high level signal can pass through the attenuator and can cause damage to the RF Mixer stage. While you can repair the mixer, some components are no longer available (think mixer diodes) but you may be able to substitute a different part that may or may not provide the same level of performance. You will need some good test equipment to trouble shoot the mixer, but at minimum a 100 MHz scope may work, along with a signal generator capable of -30 to 10 dBm and a frequency range of 100 - 500/1000 MHz. If you have equal or better equipment and time, study the service manual and the operation explanations and then start with good troubleshooting measurements.

Best of luck, keep us updated as you go. Paul/WB6GHK


Marcus - PP5MS
 

Hi everyone,

I would like to thank everyone who kindly gave me information and advice on how to proceed with the repair.

I downloaded the service manual and will start the work with a good visual inspection, changing the battery and checking the power supply.

Certainly I will publishing here the progress and I hope to have the 2712 fully functional soon.

Marcus - PP5MS