Krell DVD Showcase static

xyobgyn

Member
2011-09-13 4:43 pm
I'm about to take delivery of a pair of these, both used, they are definitely older units, dating back about 15 years most likely.

One is said to work perfectly, the other has "static" in both channels, and I'm getting it primarily for parts back up to keep the other one in service longer, or, possibly for repair and use.

There are only 4 boards inside. One for display, one appears to be off to the side to drive the transport, one is obviously the power supply, and one handles (presumably) the D/A conversion, and pre-amp section to drive the outputs, balanced XLR and RCA. (Discounting the optional HDMI board, only one of these has it)

Is it possible to generalize whether the fault is most likely in the PS vs the board for driving the outputs? I'm suspecting that on the A/D board/Preamp board that some caps are past their prime, swollen or leaking etc...

Is there much danger in swapping in the known good preamp board into the static one to test if the problem is on that board? Start with PS board swap instead?

I don't have a scope to watch the signals unfortunately, and I know that limits my ability to find the problem, but on many other projects, replacing caps has worked well, and usually visible changes are apparent. I'm just surprised Krell would not have put "overkill" caps in place where needed.

Thoughts?
 

xyobgyn

Member
2011-09-13 4:43 pm
DVD Showcase

Complete story not unravelled yet, but I think I'm on the right path.

The working one did work for a while, and it was phenomenal. Then it died. I was using the one first with no HDMI boards and mods added, there is a kit that cold be used to upgrade these. My working one (no static) didn't have the upgrade. I wanted it for CD playback only.

Internally there is a switching power supply PCB from a company called Mitsumi. It was suspicious for failure given the "brick" mode mine had adopted, not responding to any buttons or remote at all when it froze.

On the switching PS, one diode seemed to have overheated and discolored both the pads it was soldered to. Same finding the the "backup" second unit that I still haven't tried out yet. There was a second identical diode that didn't seem to overheat on the board as well. I scavenged that one from my back up unit.

I re-capped and replaced the diode with a non-overheated one from the back up. For the moment, function is restored to phenomenal sound. But its time limited, and I'll have to put in a new diode, and I'll get 4 new ones to hopefully clean this up. Unclear to me why it overheats in both units. Either it's aged poorly, or the design of the PS is not proper.
 

xyobgyn

Member
2011-09-13 4:43 pm
For anyone following in my footsteps. At the end of the day, I was able to recap both inexpensive power supply boards, as well as put in new diodes for the ones that were overheating. In the "static" unit, I was very pleased to find that the static traced to loose and poorly routed and installed flat cables. Once opened, the simple movement of the ribbon cables induced the static. I sold off both units, knowing that each had been restored to fully functioning condition and that with a new Diode in place, and refreshed power supply caps, they would serve the new owners for a while effectively. I took the proceeds naturally and bought a dedicated CD player who's entire boards are proprietary, and built in house. Unfortunately, they used transports that don't seem to last, and are NLA... and it has since stopped working. Cost of fishing in the used market I guess.