Quantar SCM fail

[Mogman]

The Quantar I am working with ran for two days then went into perpetual reboot, pulled the SCM and put in the spare I had programmed and aligned and it came right up, I looked the bad SCM over expecting to see a smoked tantalum cap or possibly an electrolytic that showed signs of distress.
I have not gone through the caps to see if any are shorted, at least in my Harris equipment they have the Courtesy of usually exploding into a ball of flame burning a chunk out of the board, makes it pretty easy to find.
Just curious if anyone has had this issue and if so what they found.

 

[UAT_978]

This is a pretty common failure. I have had them go toast merely by programming them. On the reboot, done. Near field lightning strike? Done.

I have not done a deep dive, but i suspect the EEPs are prone to scrambling with any sort of transient voltage.

 

[Mogman]

Thanks, nothing of that type happened here. she was on a very large and stable UPS and a dummy load

 

[UAT_978]

Those were just a couple of examples. The stations I manage are also on stable power and sometimes the SCM just fails for no reason.

 

[Mogman]

I have a dozen or so SCMs but would like to repair the one that failed, a failure like this is commonly a bad capacitor but of course anything is possible, going to go to the bench later and look for a shorted cap.

 

[OpSec]

It just happens. Sky has a cloud? Done. Bird flew too close? Done. Power cycle? Done.

They are only stable if they don't get power cycled and are left to just run. It's a great base, but the SCM and power supplies are their weak spots.

 

[KevinC]

It just happens. Sky has a cloud? Done. Bird flew too close? Done. Power cycle? Done.

They are only stable if they don't get power cycled and are left to just run. It's a great base, but the SCM and power supplies are their weak spots.

And if you see dust on the power supply vent holes DO NOT dust it off while the unit is powered up. I always thought that was a myth until I was at a 27 channel 4.1Z SZ site and the air conditioning was out. I found a huge fan and turned it on and aimed towards the stations. After a few seconds I started hearing loud pops, the guy I was with yelled to turn off the fan. Fortunately we only lost 5 power supplies.

 

[prcguy]

And if you see dust on the power supply vent holes DO NOT dust it off while the unit is powered up. I always thought that was a myth until I was at a 27 channel 4.1Z SZ site and the air conditioning was out. I found a huge fan and turned it on and aimed towards the stations. After a few seconds I started hearing loud pops, the guy I was with yelled to turn off the fan. Fortunately we only lost 5 power supplies.

Did you have to update your resume after that incident?

I dusted off the PS vent holes on my own Quantar while it was running in my own garage and the PS died and I got fired for that. I beat myself up and threw myself out of my garage.

 

[KevinC]

Did you have to update your resume after that incident?

Fortunately this wasn't a RGE.

 

[Mogman]

These things can be very frustrating.

 

[Mogman]

It has been many years since I messed with these things, so evidently the first box of SCMs I found were the duds, out of the cards I have tried 5 have no repeat audio, I see a post about a MAX filter chip going bad on the TTN-4094 board, most of mine are CLN-6961C boards. I wonder if it suffers from the same affliction? they do have the same chip on board.
2 would no sync up the TX-RX even though it showed the high stability osc. operational, but these CLN-6961C boards have the front reference injection port removed so I figure they were modified for some reason.
I did find another box of SCMs, some still in padded envelopes so I will give them a try.
The board that worked fine for 2 days before it started perpetual reboot was a CLN-6961C
The only one that is still working is one of those strange ones a CLN-7098
Edit, all of the boards that would not repeat audio (analog or P25) would go through alignment OK

 

[Mogman]

I am also getting more gray hair every time I wait for the osc to warm up.

 

[Mogman]

Yep, that's what I did, the first board out of the second box works perfectly, I bet 10-15 years ago that I thought I would remember which was what.
I mark everything now cuz I can't remember what I ate last night.
Well if that chip is the issue with all the no repeat audio boards then it will be an easy fix and I can re-hone my SMT skills...

 

[jmfirefighter]

I've had several go bad during programming sessions. Ended up being the little square IC on the board that contains the programming and other information.

The chip was readily available on Digikey or Mouser....pop the old one out, drop the new one in, programming, and we were off to the races.

 

[Mogman]

I've had several go bad during programming sessions. Ended up being the little square IC on the board that contains the programming and other information.

The chip was readily available on Digikey or Mouser....pop the old one out, drop the new one in, programming, and we were off to the races.

The mass of them program up fine, I do remember there was a "bad" brand of chip, I will have to look that up but IIRC it caused programming issues,

I've had several go bad during programming sessions. Ended up being the little square IC on the board that contains the programming and other information.

The chip was readily available on Digikey or Mouser....pop the old one out, drop the new one in, programming, and we were off to the races.

Thanks for reminding me, I just ordered a stack of ATMEL AT28C64 chips

 

[UAT_978]

And if you see dust on the power supply vent holes DO NOT dust it off while the unit is powered up. I always thought that was a myth until I was at a 27 channel 4.1Z SZ site and the air conditioning was out. I found a huge fan and turned it on and aimed towards the stations. After a few seconds I started hearing loud pops, the guy I was with yelled to turn off the fan. Fortunately we only lost 5 power supplies.

I had a customer do that and the power supply exploded while his hand was still on It.

Talk about having to explain that one to them.

 

[Mogman]

I thought I had a bunch of bad SCM cards, what I found is if I align the radio with the measured deviation under 4Kc even if it was under 4 Kc the radio would not repeat audio, no idea why but replicated the problem on 5 different SCM cards.