Because the original Sony power supply is UNREGULATED, the nominal 10.5V and 5.2V output Voltages vary considerably.  And they have about +/- 0.5V ripple on them so digital measurements are a little variable depending on when the measuring device "samples" the Voltage level.  I also discovered that these output Voltages drop when the AC line Voltage drops.  For example if the nominal AC input is 120VAC, and I turn on a space heater plugged into the same circuit, the input drops to about 110VAC.  The Sony's power supply outputs fall accordingly.  I suspect this is why the regulated 8.5V in the tuner is actually 8.2V: Sony knew the unregulated nominal 10.5V output would drop as low as about 9V along with a drop in line Voltage.  That could cause the 8.5V regulator to drop out.  So they deliberately designed the 8.5V output to actually be 8.2V.  That's my theory.

As Mr. Spock might say: Fascinating!  

Heat Damage to the Case

I'm seeing increasing numbers of XDRs with long-term heat damage affecting the plastic case.  The most common point of failure is at the mounting posts for the transformer.  That transformer gets VERY hot.  Eventually the plastic screw mounts for the xfmr become brittle and crack.  They literally fall apart.  Here's an example with both posts broken off.

I've been experimenting with transplanting the Sony's power supply to an external case as a way to reduce heat in the tuner itself.  I didn't expect this to work well without a vented case for the power supply and possibly its own fan.  Surprisingly, the power supply runs very well even in a completely enclosed case with no venting at all.  At an ambient temperature of 29C, the top of the case levels out at about 35C.  The maximum measured internal component temperature is about 45C.  In a cooler ambient environment of about 22C, the external and internal temps are correspondingly lower.  Some heat from the transformer is conducted through the mounting bracket to the aluminum case.  These measured temperatures are all perfectly acceptable.  Very promising! 

7/7/2015 More Information About Heat Damage

An XDR owner recently sent me a non-working tuner which I agreed I'd try to repair for him.  It turned out the tuner was severely heat damaged.  The first issue I found was the power supply not working right because both of the main aluminum electrolytic capacitors in the power supply had failed.  Replaced them, power supply worked again, but the tuner sounded bad and the HD module didn't work at all.

Long story short: Every single aluminum electrolytic capacitor on the main board (the blue cans in the photos) had technically "failed": They all measured at least 50% out of tolerance, with a couple being like 90% out of tolerance.  I replaced all of them, which got the XDR sounding good again.

Unfortunately though the HD module had suffered heat damage too.  These modules are a "black box" full of unmarked mini surface mount parts.  Nearly impossible to work on without schematics etc.  The cost of a new HD module is more than the value of the tuner.  So this XDR's analog tuning ability was restored but unfortunately without HD.

The photos below show the long-term effect on the XDR's main board from running the tuner continuously without fans, vs. what a brand new XDR main board looks like.  The board in the top photo is literally heat-scorched around voltage regulators (most of them are on the solder side).  It even smells burned.  Amazingly, the board still worked.

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XDR Heat Problems

Graph of the internal temperature measured in the open space between transformer & tuner module

(probe not in contact with any internal components)