Author Topic: Stabilock 4032, doubt w/capacitor replacements & RF stages  (Read 975 times)

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Offline victroniko

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  • Country: cl
Stabilock 4032, doubt w/capacitor replacements & RF stages
« on: February 01, 2020, 05:43:27 am »
Hi to all, 1st post from this newbie on the forum :)

To the point: I've scored a wonky Schlumberger Stabilock SL4032 RF analyzer from my job. Long story short: failed 6-7yrs ago, was gathering dust all this time, recently we changed work location & higher-ups didn't want to haul "old junk" to the new place. This unit is modular & has a nifty Self-Check routine that sadly, show problems on specific backplane-mounted boards. And indeed, on said boards there are a bunch of leaky caps :palm: so I'm on the process of repairing the (fortunately not so extensive) damage and replacing all of them that seem dubious.



I know that for supply rails I can replace electrolytics with same-or-sligthly-higher volt & uF ratings w/o negative effects. ¿Can I do the same for RF related stages, or it might de-characterize them? I'm specially cautious of the IF and AF boards because don't want to leave them out of spec.

The replacements on these stages would be (11x) 22uf 35v in place of 22uf 25v & 16v, and (2x) 10uf 63v in place of 10uf 50v. The reason is that I already have them, if I order the exact ones it'll take some weeks before they arrive where I live.

Thanks & hope you're all ok!!
 

Offline Astralix

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  • Country: de
Re: Stabilock 4032, doubt w/capacitor replacements & RF stages
« Reply #1 on: February 20, 2020, 10:18:08 pm »
Hi!

The service manuals are out there, just google them. And then apply the three golden rules of electrolytic capacitors of that time, where this unit was built:
1) Exchange all electrolytic caps.
2) Exchange all electrolytic caps, that just looked fine.
3) Exchange all caps that you forgot.

In the service manuals there are lists of all parts. I have a SL4031 and I used google tabs to ma a list of all parts. As almost all of the capacitor manufacturers listed in the service manual have vanished form the marked (probably as all their caps leaked), Schlumberger advised their service personell to replace all caps by Panasonic branded ones of the same types. Please watch out for discoloration of parts and PCBs around these Caps, especially the SMD ones. You have to clean these areas very very thoroughly. On the RF boards, check the vias.

I do not see any problems in replacing them with the same values, but remember that, the higher the voltage rating is, the higher the chance, that the cap is positive in tolerance. So look for same µF value but higher voltage. But (yes, there is always a but) be careful of the sizes. It makes no difference in putting a 2mm pin distance into a 2.5mm hole layout. But trying to solder an 6.8mm SMD cap onto 6.2mm pads does make big problems...

Other than that: First start with the power supply. With a chance of slightly over 154% the -15V are pretty unstable. Use good quality caps for the replacement. I used 732-9534-1-ND and 732-9612-1-ND from digikey and I also replaced all other caps in the PSU with Würth.

Advise for the plug-in boards: Handle with care and using ESD strip is a must, must, must! Some very important parts of this unit are not available anymore. For example, on the 433,92MHz oscillator  is a BFG92A, that I cannot find anywhere. BFG92A/X are available from a broker and are also relatively cheap, but the pinning is not the same. The A has the two Emitters on one side, the A/X has them across each other.

If you have more questions, just ask :)

73!
 

Offline BretRDR

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  • Country: us
Re: Stabilock 4032, doubt w/capacitor replacements & RF stages
« Reply #2 on: June 11, 2021, 10:31:46 pm »
I managed to score two SI4031 over a year ago for a great deal!
I deal with IT and Networking but radio has been an integral hobby and pastime, however I am being asked to help with more hilltop work and testing lately.

The first unit from ebay had a power supply fail and the last owner scrapped it. He built a temporary supply for testing and everything checks out so I need to build a permanent PSU for it.
The second unit I bought from a Canadian test equipment company for parts as I was assured it was braindead. Imagine my amusement after mashing the power button on and off aggressively to hear a whine and see a picture. It managed to pass a self-test and let me into the menus before giving out and shutting off with bad voltages. This can be repeated once things sit for a while disconnected. One of the RF engineers in the state who I respect very much recommended these and did mention replacing all of the caps in them before any serious use, and that seems to be the consensus amongst other users. I need to get at least one working and am getting ready to order new caps for the lot.

Atralix, do you still have the list of parts especially the list of caps? If so would you please email/PM those over?
 

Online Aheld

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  • Country: de
Re: Stabilock 4032, doubt w/capacitor replacements & RF stages
« Reply #3 on: July 11, 2021, 04:37:50 pm »
Hello BretRDR,
5 years ago, I repaired my 4032 by changing all SMD and THT Caps. Really all, approx. 250 pcs. This was the only option to reactivate my 4032. My experiance was that 4032/4031 works very relailble but had some issues with bad capacitors. You can find the servicemanual in web and is very helpful  :)
 


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