Barrett SB550 Schematic

[Yipyip46]

Help needed! I have a Barrett SB550 with a fault in the P.A. stage. I have a copy of the Service Manual that has the schematic for a Version A1. The P.A. PCB in this radio
is a 550 P 03 A3 and the fault is in the area where the difference is. Unfortunately Barrett cannot help with the newer schematic. They only have the original A1 version.

The original fault was several tantalum capacitors had gone short circuit and taken out a switching transistor and other components.

I look forward to hearing from people can help.
Regards
Ian.

 

[merlin]

If I recall, the 850 was near identical, maybe a newer schematic/SM can help.
Those tantalums were a common failure in the 550.
I have a 980 in need of alignment which I believe is softpots done with software. Seems unobtainium.
I have the scematic for the 900 if that may help
My 980 is significantly different, Different devices and layout. Right after that, Barrett tossed everthing into the dumpsters, switching to the 4050 and 2050. So what is still out there is salted away in some hams file cabinet

 

[Yipyip46]

Hello Merlin, Thank you for your prompt reply. I have looked at the schematic and again it is close but is missing a few components. The A3
version has U6 as a 78L05 and C88 as a 10uF 16V tantalum. The output stage and filters are almost identical.

I know what you are talking about when you talk about the software. I don't have access to it but I know of a Ham on the north side of Brisbane who has a copy but no test gear to connect the radio to.

I used to have contact with several of the older techs at Barrett but I believe they have moved on.
Regards
Ian

 

[merlin]

I have a bit of programming software. I downloaded some for the 4050 and 2050 but doubt I will ever afford one.
My first Barrett was a 550 with land pack. Had that in my semi and car. a combo ham/CB. Wound up getting stolen then got the 980 to replace it.
The big difference between the 550 an 980 is no physical tuning points except front end. (Why I suspect softpots)
Sad part is NEC trashed everything for the CPU, so very hard to hack. If there are functions for tuning in firmware, I might be able to write a Python app for tuning these. Since Barrett sold to Motorola, they know of no software for these radios.
Hey Ian, perhaps see if that Brisbane ham has any software I dont. I have been ferreting the web for anything older like this.
Dan