Anritsu MS2602a spectrum analyzer repair help

[lectrohamlincoln]

Hi,

I just picked up a Anritsu MS2602a 8.5Ghz spectrum analyzer for free! However, it does not display any signal and it appears the A/D board has gone bad.

I suspect the A/D board for two reasons: the flow chart in the service manual vol 1, and when I took it apart the A/D board had a piece of masking tape with a big black X on it

The service vol 1. doesn't offer much in the way of diagnosing circuit level problems and it appears the service manual vol 2 is IMPOSSIBLE to find. I've done some rudimentary test, such as checking all voltage at labeled rails (all voltages good so far), and now I'm at a loss as to how to proceed.

Do you guys have any suggestion on what I should check next? Or where I might find the Service Manual vol. 2, a replacement A/D board, or even an extender so I can take the board out while the MS2602a is powered on?

[OK1DXD]

Hi,
I bought mine a half year ago. After a few month of service failed. On power up everything works fine, but no real trace on the scope, only straight line on 0dBm level. Im suspecting AD or LOG detector module. Unfortunately there are no detailed service manual available what makes there repair near to impossible  I inspected boards inside the case, there are a few capacitors with electrolyte leakage on LOG/DET board, the PCB seems to be destroyed a bit under the capacitors. The -15V line has a short to ground. There is a multiplayer PCB which is very difficult to repair.
The predecessors = MS2601A (from year 1988) has very well service manual with detailed circuit description, but still found not something similar for MS2602A
Probably will sell it for repair parts only 
Tomas

[razberik]

That sounds interesting. Post picture of problem board.

Or would you like to sell it ? How much for local pickup ?

[nctnico]

@lectrohamlincoln: A very effective method is to get the datasheets from the chips on the board so you can determine function (groups) and see if the signals make sense. In a spectrum analyser you'll typically have a second IF output which has a signal with a low enough frequency to measure it using an oscilloscope. With a small (or zero) span and a signal connected to the input of the spectrum analyser you should be able to measure it with the oscilloscope and then trace it through the analog section. The key is to measure step by step first and don't start replacing stuff blindly because that will do more damage than good.
Can you post a high-res picture of the board?

[lectrohamlincoln]

Hello, sorry for long response time.

@nctnino: thanks for the advice!

I'm pretty sure I managed to track down the problem to ADC itself. But, I discovered that the A5 Scan board is the same board used in later model MS8604A. Luckily there was one on ebay too. Replaced the board and the Spectrum Analyzer is working!

I'll post some pictures when I get a chance

[OK1DXD]

Dobrý den, omlouvám se že odpovídám až po tolika letech. Přístroj bych prodal za 9.500Kč. Pokud byste měl stále zájem tak prosím napište na ok1dxd@seznam.cz
s pozdravem