DIYbanter - View Single Post - Revox B251 Integrated Amp No Output and More

Tim Schwartz[_2_]

On 2/5/2016 8:58 AM, wrote:
Before I dive in blind, here are the symptoms:

This amp, which had worked nicely at our summer house (seasonal use) for 4 years died one evening - slowly going quiet over about 30 minutes (I was drowsing at the time and did not notice the problem until about the final 2 minutes). No heat, no smoke, no fan operation, no smell. I turned it off for an hour thinking a part may have overheated. When I turned it back on, it promptly blew the main PS fuse. This is a solid-state 100WPC amp built as with many things Revox like a tank. LCD display, capacitance controls, and so forth. It is also IR remote-capable.

I removed the unit from service and brought it home. Last night, after about a 18 months, I decided I would look it over. I replaced the fuse, and brought it up slowly on the variac. The first time, it drew about 45 watts, quiescent, no activity, no display, no pilot light. When I activated the on/off switch, the display went wonky - random pixels, random words, but no activity. No controls, including on/off responded after that point, but the draw went up to about 65 watts. I shut the unit down and held the on/off switch for 40 seconds (hey, it sometimes works with computers and other devices containing computers). This time, when I applied power and reached about 120V, the fan came on, the display showed other random stuff, but still no activity.

At this point, I decided that without direction, I would likely do more harm than good at random.

Thoughts? Suggestions? I am searching for the manual from HiFi engine, but I am also hoping that someone out there may have had some experience with these beasts.

Peter Wieck
Melrose Park, PA

Hi Peter,

I have NOT worked on a B251, but I have work on several B750's and
other Revox products. I have often seen small 'bead' style tantalum
caps short in all sorts of circuits. While I'm not a fan of wholesale
replacement of capacitors, I'd ohm-meter them if accessible and change
as needed. I'm not a huge fan of tantalum caps in power supplies, they
have very low leakage, but are very intolerant of over voltage or
reverse voltages.

Regards,
Tim Schwartz