Normal for diodes to be really hot?

[gadget73]

Looks like these are mostly "500" series parts. If this is like other things, you'll find that all of one board will be 100's, another will be 200's, etc. Assuming this is the case, and further assuming that D505 on the schematic is marked D5 on the board, it is indeed a zener diode. Looks like R503 is your current limiting resistor. Physically speaking, R503 on the board is right next to D5, so if they are connected, its a reasonable assumption.

I do see other parts on this board with "500" part numbers, so it might be marked as D505 and just be partly blocked.

 

[ic-racer]

Are you sure R105 is not the hot one?

 

[birchoak]

I’d be replacing those electrolytics
The one just to the right looks like it spilled it’s guts
Electrolytics hate heat, that electrolytic might be a near dead short causing you some issues which may be contributing to the hotter than normal diode which in turn is destroying capacitor(s) etc etc

Good call; actually, that is residue left over from the old caps. I scraped and acetoned as best I could before putting in the new Nichicons.

 

[century tek]

So, you were curious and just decided to take the top off and look and feel around, and you discovered something even though the receiver was working nicely with no smell or smoke or anything?

 

[birchoak]

Here is the PS section from the Concept 2.0 schematic in AK's database. BUT, I don't believe it matches the pic above. Can someone else please confirm or deny?

In the schematic it shows a bridge rectifier. The pic shows four individual rectifier diodes D503-D506. The schematic shows D505 as a zener. The pics shows D505 as one of the rectifiers. I see no D5 in this schematic.

@birchoak does your schematic look like the one posted below?

View attachment 1453208

Yes, that is the schematic I have. I stand corrected, the diode in question is D509, not D5, and yes, everything on this board is a 500 number.

 

[birchoak]

So, you were curious and just decided to take the top off and look and feel around, and you discovered something even though the receiver was working nicely with no smell or smoke or anything?

When a man gets a new infrared thermometer, expect him to go measuring things! I ran into some problems when I recapped it, so I wanted to make sure things were relatively ok in there. But yes, it seems to be working perfectly and sounds, gods, this thing sounds amazing.

 

[birchoak]

You should do a close inspection of the back side of the board under those components. There could be compromised solder joints or PCB tracks/pads. If you do any soldering, be on the lookout for damaged or lifted pads.

I looked again. I redid pretty much every single solder joint, but it's worth checking again. It's the obvious that eludes us, often.

 

[birchoak]

Ok, here's some more data, taken at idle.
* On the power supply board, B+ shows 27.8 VDC (I'm assuming I should be using the DC scale; if not, pardon my ignorance) and B- is -27.8V. I'm guessing that's ok for a 20 watt receiver.

* Voltage at cathode of extremely unhappy diode D509 is 24.7VDC; 0.0 VDC at anode. It is 152˚F at the anode.
* Voltages at + poles of filter caps are 27.7 VDC and -27.6 VDC. Probably about right?
* R507, that small resistor next to suffering diode D509 is 222˚F! And I thought D509 was having a bad day. DC voltage at this resistor is about 24.5.
* R503 showed 12.9V (I'm guessing it's part of different power path--lighting or something?) and was 167˚.
* R505 showed 30.9V (kinda high?) but was a relatively balmy 99˚.
* Capacitor C513 is also rather unhappy, clocking in at 120˚.
* Power transistors read 20.0VDC for outers; 0.00 for inners.
* DC offsets are negative numbers, R -0.19mV L -20.0mV, but I think the multimeter I used for this particular measurement just went south.

I don't know if this has anything to do with anything, but there's a red wire leading from a small board under the chassis to a post in the center of the power supply, underneath it. This sucker reads 42VDC and that seems high. Perhaps that excess voltage is being converted, with great reluctance, into heat by the above too-hot components? Here is a pic of that weird little board:

 

[birchoak]

I swear that green thing moved when I wasn't looking.

 

[roger2]

Ok, here's some more data, taken at idle.

* Voltages at + poles of filter caps are 27.7 VDC and -27.6 VDC. Probably about right?

One of the main filter caps' + terminal should be connected to ground so should be reading 0v

There is a lot of information in that post. The temp readings are interesting and likely further indicate problems. But for resistors, voltage readings should be taken at both ends. That would allow voltage drop, current, and power dissipation to be calculated, assuming that the resistance value is also known.

I have no idea what that 8-legged green thing is

I think you are looking the wrong schematic if is it the same as the one attached to post #20 from the AK database. Diodes D503-D506 on the PCB do not match what they appear to be on the schematic. There are other discrepancies. IMO, seeking out the correct schematic is priority one at this point. Troubleshooting gets out of hand confusing when there is too much superfluous information floating around.

 

[birchoak]

One of the main filter caps' + terminal should be connected to ground so should be reading 0v

There is a lot of information in that post. The temp readings are interesting and likely further indicate problems. But for resistors, voltage readings should be taken at both ends. That would allow voltage drop, current, and power dissipation to be calculated, assuming that the resistance value is also known.

I have no idea what that 8-legged green thing is

I think you are looking the wrong schematic if is it the same as the one attached to post #20 from the AK database. Diodes D503-D506 on the PCB do not match what they appear to be on the schematic. There are other discrepancies. IMO, seeking out the correct schematic is priority one at this point. Troubleshooting gets out of hand confusing when there is too much superfluous information floating around.

I agree. There just isn't much information on these receivers. I may simply rebuild the power supply (beyond the capacitors, which I've already done) and call it good. Enjoy it as long as I can while the fun lasts. It is an extraordinary sounding receiver and that's why I've been burning some calories, 20 watts notwithstanding. One end of each resistor is pulled tight to the board, necessitating and under-the-board guess on whose leg is whose, and I don't trust myself. But what you say makes sense. I apologize for giving too much of the wrong data, but data was delivered nonetheless.

 

[roger2]

Yeah, I looked around at a few free manual sites and all I found was the one that is already in AK's database. I apologize for causing you to apologize, lol. Someone smarter than me might be able to solve this puzzle by putting together the bits of information you provide. So keep on doing it. But as for me, without the correct schematic I'm afraid I won't be of much use to you. I would advise NOT rebuilding the power supply without proper parts identification.

 

[birchoak]

Yeah, I looked around at a few free manual sites and all I found was the one that is already in AK's database. I apologize for causing you to apologize, lol. Someone smarter than me might be able to solve this puzzle by putting together the bits of information you provide. So keep on doing it. But as for me, without the correct schematic I'm afraid I won't be of much use to you. I would advise NOT rebuilding the power supply without proper parts identification.

Advice heard and taken. Wow, you caught me fast. The easiest thing might be to buy another Concept 2.0, don't touch a thing in it, and compare the two. Unless they all start running hot power supplies. I dunno. I don't think it's a question of smarts on your part; I'm good with my hands but I have much to learn about electronics. Thank you for helping out, regardless. I may simply take it to a professional tech here in MA. It's that good a receiver. Too bad the voltages, etc. aren't available to the public so we have a shot at keeping these magnificent instruments alive.

 

[roger2]

Getting another Concept 2.0 and comparing is a good idea. Keeping an eye on eBay for a proper Service Manual might be a good idea, as that would be very helpful. Perhaps one of the non-free manual sites would have it, I don't know.

 

[audiodummy]

Kind of funny, yeah:
1-The schematic is close, but not exact. Might be a different revision but 2.0 is oddly enough supposedly a revision.
I think the circuit is the same but component designations are different.
Looking at the schematic, my guess is that the originally R-D5 (later revised to R-D509) diode may be S-D504, and it should not be getting hot. However this is only a guess.
This guess is based on S/R-D501 and S/R-D502 which should be regular diodes and the there is only one more regular black diode on the board, S-D504. You mention that the anode is 0V, which matches the schematic, and cathode could be anything - I think it's reversed biased and should not be heating up. The two zeners appear to be orange colored glass things, S-D505 in the upper right and S-D503 near the designation R-C508 on the board.
Note: S-XXXX I mean the designation on the Schematic, R-XXXX is the designation on the Real board, and S/R-XXXX when my guess is that they match both schematic and the real board.
2-It would be nice to see the underside of the board with the tracks, someone could reverse engineer what's going on there.

If you're using one of those laser pointer IR thermometers, be sure you're pointing at the right spot, might be off. You could try a piece of aluminum foil taped up in clear plastic on both sides (for electrical insulation) and slide it underneath a part you're not sure of, so you're not getting the temperature of a nearby part.

Not saying that the temperatures are incorrect, but I have a hard time aiming mine

 

[cpt_paranoia]

Here is the PS section from the Concept 2.0 schematic in AK's database. BUT, I don't believe it matches the pic above. Can someone else please confirm or deny?

There any many common elements between that schematic and your picture. So, I suspect iti is functionally equivalent, but the circuit references may be different.

For instance, the scm shows a bridge rectifier (D12), whereas your board has four discrete diodes forming the bridge (on the left; the four upper diodes with round, grey-coloured bodies, probably sintered glass, seemingly marked D503-D506). There's an SCR too, probably for crowbar protection. There also appears to be a transistor, that may be TR501, looks like a seiries voltage regulator with D503. A failure of that circuit could cause excessive volts across zener D505, which may be your D5 on the PCB.

The scm shows three 3W resistors in various places. Looks like two may have been up-rated; the two surrounding your hot D5 (probably R503 & R505 on the scm, with the other being R506 on the scm, in series with the crowbar SCR)..

Not sure if some of the electrolytics have been replaced; the three on yhe right look to have been replaced, or else they have leaked... There appears to be an outline of the old caps. If PSU filter caps have gone dry, that could cause escessive voltage/ripple in the diodes, which would overheat them. Look for ripple across the electrolytic caps (ACV on a MM, or use a scope).

Shame the schematic doesn't have any useful markings like expected voltages.

 

[birchoak]

Is there a resistor someplace in series with the diode? If the voltage across the resistor could be measured, then current could be calculated.

I will check! That totally makes sense.

 

[birchoak]

Kind of funny, yeah:
1-The schematic is close, but not exact. Might be a different revision but 2.0 is oddly enough supposedly a revision.
I think the circuit is the same but component designations are different.
Looking at the schematic, my guess is that the originally R-D5 (later revised to R-D509) diode may be S-D504, and it should not be getting hot. However this is only a guess.
This guess is based on S/R-D501 and S/R-D502 which should be regular diodes and the there is only one more regular black diode on the board, S-D504. You mention that the anode is 0V, which matches the schematic, and cathode could be anything - I think it's reversed biased and should not be heating up. The two zeners appear to be orange colored glass things, S-D505 in the upper right and S-D503 near the designation R-C508 on the board.
Note: S-XXXX I mean the designation on the Schematic, R-XXXX is the designation on the Real board, and S/R-XXXX when my guess is that they match both schematic and the real board.
2-It would be nice to see the underside of the board with the tracks, someone could reverse engineer what's going on there.

If you're using one of those laser pointer IR thermometers, be sure you're pointing at the right spot, might be off. You could try a piece of aluminum foil taped up in clear plastic on both sides (for electrical insulation) and slide it underneath a part you're not sure of, so you're not getting the temperature of a nearby part.

Not saying that the temperatures are incorrect, but I have a hard time aiming mine

I will take a picture of the underside. Yes, I kept thinking about that when I was using the infrared thermometer (and how well the laser pointer lined up with the actual infrared sensor)--that is a a great idea with the aluminum foil. I did touch a finger to one of the resistors because I thought maybe the tool was bad and yep, it was freakin' hot!

Voltage reading at B+ on the PS was 27.8VDC (I get confused when to measure in DC and when to test in AC, so correct me if I'm wrong) & -27.8VDC at B-. I got 27.7VDC at the + pole of one of the filter caps; -27.6VDC at the + pole of the other filter cap. Since there are absolutely no published voltages for this thing--schematic does not have them, for reasons I cannot fathom--it's anyone's guess if these values are ok.

The only thing that seemed weird to this unwashed amateur was a reading of 42VDC in the center of the PS board, on the underside. It was at a post which has a red wire wrapped around it. If the MV-13 diode replacement doesn't help the problem, I thought, "Hey, disconnect that red wire and see if the board stays cool." Also, I may try pulling the PRE/MAIN jumpers and seeing if that "cures" the problem. It's all about diagnosis, right?

 

[birchoak]

Getting another Concept 2.0 and comparing is a good idea. Keeping an eye on eBay for a proper Service Manual might be a good idea, as that would be very helpful. Perhaps one of the non-free manual sites would have it, I don't know.

From what I've seen and heard, there is no service manual. I'd be happy to pay to pay for one at this point, especially if it tells me the danged voltages! I will look again. If all else fails, I will pay to have this fixed. Just not right now as funds have been tight.

 

[birchoak]

There any many common elements between that schematic and your picture. So, I suspect iti is functionally equivalent, but the circuit references may be different.

For instance, the scm shows a bridge rectifier (D12), whereas your board has four discrete diodes forming the bridge (on the left; the four upper diodes with round, grey-coloured bodies, probably sintered glass, seemingly marked D503-D506). There's an SCR too, probably for crowbar protection.

What is crowbar protection, good sir? And what's an SCR?

There also appears to be a transistor, that may be TR501, looks like a seiries voltage regulator with D503. A failure of that circuit could cause excessive volts across zener D505, which may be your D5 on the PCB.

So replace that sucker? I will happily rebuild the entire board if that puts the cure on the hurt.

The scm shows three 3W resistors in various places. Looks like two may have been up-rated; the two surrounding your hot D5 (probably R503 & R505 on the scm, with the other being R506 on the scm, in series with the crowbar SCR)..

They look like very large resistors to me. For such a low watt machine.

Not sure if some of the electrolytics have been replaced; the three on yhe right look to have been replaced, or else they have leaked... There appears to be an outline of the old caps.

That is glue from the old caps. I scraped and cleaned with acetone and yeah, it looks terrible. But this thing has all new caps in the PS and the amp board, as well as brand-new Kemet screw terminal filter caps.

If PSU filter caps have gone dry, that could cause escessive voltage/ripple in the diodes, which would overheat them. Look for ripple across the electrolytic caps (ACV on a MM, or use a scope).

Hmmm. Maybe I got a bad cap and didn't know it? Again, I will gladly pull all the caps and start over if it's just a darned cap.

Shame the schematic doesn't have any useful markings like expected voltages.

Oh man, don't I know it. I'm still learning how to read schematics, but I always say, "Oh yeah!" when I find a voltage spec on a schematic.