[addaz]

Hi folks.

Yesterday I completed my Bugle PS and it turned on with no problems on the first try! I checked the output voltages of both channels and they were at a near perfect 14.9xV. I left it on for just over an hour, intermittently checking the output voltages and checking for hot components the whole time. Everything was kosher so I shut it off.

Later last night I decided to test a few different LED colors in the circuit to see which one would be best. I plugged it in and tested the output voltages. Both channels were at a near-perfect 15V. I visually checked the polarity of a random crystal clear LED and touched it to the LED +/- contacts on the board. Nothing happened. I tried another and another to no avail. I tested one backwards and still got no light.

I check the fuse holder and sure enough I blew a fuse. I plugged another one in and went back to testing and was still getting nothing so I checked the fuse again and it was blown. Now I realize something is wrong so I posted this problem over at another forum. While waiting for a reply I decided to plugin a fuse and see how long it takes to blow. I plug one in flip the switch and immediately put my DMM on the output of one channel and it's rapidly dropping from 14.9V to near 0V.

I'm at an impasse.

I took my time building this unit and double checked my parts and polarities before soldering and since this problem has started I've quintuple checked this circuit and can not find a single thing wrong with it on a visual level. All cathodes are in square holes and all positive leads on the caps are in square holes. Voltage regulators are in the correct spot. All solder joints are shiny. The fuse I'm using is a 63mA slow blow and it's not available locally and I'm quickly running out of them (only two left.)

The general consensus is that it's a simple problem that's causing this (and I agree) but I'm stuck. What could be the culprit?

Here's a bad cell phone pic as I'm on my out the door. The IEC is a switched-entry. I'm floating ground because It's not in a chassis.



Please let me know if I can provide you with any more info or if anything is unclear. Thanks for reading this tome!

[addaz]

In an effort to over-inundate you with information here are some better pics of the circuit. I accidentally ordered all metal oxide resistors except for one. They are all 1W.

Diode polarity:








U1 is 7815:


U2 is 7915:


Switched entry rear:


Fuse holder:


Transformer wiring:


Would having the fuse after the switch make a difference?

[poty]

1. The PS wired for 115V - is it correct? For me - the place of the fuse in the mains circuit is not important, the main and the only rule it has to be in serial with the device. From that point of view I don't see any problem here.
2. From your description it seems that the fuse blows even without any load (including LEDs)? Then it may be a lot of things. To save valuable fuses you can use much more powerful and widely available 0.5-1A fuses for testing. Try to add an usual 10-25W 110V filament bulb in serial with the fuse circuit or power the device through a variac. It'll help to reduce current to the device and allows to make measurements in several points (many values are marked in the manual).
3. If the above precautions doesn't help the only way to test is gradually enable parts of the device. I'd begin with unsoldering R1 and R11 (to check if the transformer is in order after powering on). Then put the resistors in place and unsolder R2, R12 (check if D2, D3, D5, D7, C1, C4 are OK after powering on). Then restore the resistors from the previous step and unsolder U1, U2 (check C2, C5 after powering on and C3, C6, D4, D6 for breakdown). If nothing of the previous steps reveal problematic part, the only parts left are U1 and U2.

[addaz]

Thanks for the detailed supply, poty. This circuit is wired correctly for 115v according to the additional Power Supply Notes PDF supplied by jcg0322. You're correct in assuming the fuses blow without any load; however they didn't start blowing until I tried to apply a load.

As soon as I get home from work I will begin troubleshooting.

After removing R1 and R11 you  say to check and make sure the transformer is working. Would I do that by measuring output voltages (those are the only voltages I see to check for on the schematic?) I know, dumb question but at this point I want be as thorough as possible.

[poty]

This circuit is wired correctly for 115v...

OK

You're correct in assuming the fuses blow without any load; however they didn't start blowing until I tried to apply a load.

Understood.

After removing R1 and R11 you  say to check and make sure the transformer is working. Would I do that by measuring output voltages (those are the only voltages I see to check for on the schematic?)

Addaz, we all know that we can't know everything, so asking questions is one of the way to know more. I'm glad to help. Hope we'll chase the problem. I should write this before, but didn't have enough time to do this.
As far as I understand you are going to start with the third approach? Well...
After you remove R1 and R11 you should measure AC!!! voltages on the R1 and R11. They should be more than 21V (it is marked on the schematic). If even after the removal the fuse blows - then problem is in the transformer or its wiring on PCB traces.
After you remove R2 and R12 (the R1 and R11 should be put in place) you should measure DC!!! voltages on R5 and R8. They should be more than 20V (it is marked too). Blowing the fuse in this case means possible breakdowns of D2, D3, D5, D7 or C1, C4.
After you remove U1 and U2 (the R2 and R12 should be put in place) you should measure DC voltages on C2 and C5. They should be more than 19V (marked too). As soon as the rest of the curcuit will be separated you can use a DMM to check if the C3, C6 or D4, D6 is working (positive probe - to positive of C3, negative probe - to the negative of C3, resistance should be very high. Then the same thing you should do with C6).
If all is OK after the last step - you should try to replace (one at a time) U1 and U2.

[addaz]

Hi Poty. Here's what I've done so far in order:

-Installed 250mA slow blow fuse (closest to 63mA I could find locally.) I measured close to 0VDC on the 15V outputs.

-Removed R1 and R11 and measured 24.9V AC in their places. Fuse is good.

-Installed R1 and R11. Removed R2 and R12 and measured 33.5V DC in their places. Fuse is good.

-Installed R2 and R12. Removed U1 and U2. I then measured 33.43V DC across C2 and C5. Fuse is good.

As soon as the rest of the curcuit will be separated you can use a DMM to check if the C3, C6 or D4, D6 is working (positive probe - to positive of C3, negative probe - to the negative of C3, resistance should be very high. Then the same thing you should do with C6).
If all is OK after the last step - you should try to replace (one at a time) U1 and U2.

So I'll be measuring resistance across C3 and C4 (capacitors) and then measuring resistance across D4 and D6 (diodes) and then C6 (capacitor?) I only need to test those two diodes?

When I replace U1 and U2 where do I measure to see if they are working ok? Also, when you say to install them one at a time would that mean Install U1 take a measurement then remove U1. Install U2, take a measurement then remove U2.

Or does it mean install U1 and take a measurement and then install U2 and take a measurement?

Thanks so much for all your help so far! 

[poty]

Hi Poty. Here's what I've done so far in order:
-Installed 250mA slow blow fuse (closest to 63mA I could find locally.) I measured close to 0VDC on the 15V outputs.

Have you tried to power on full device with the fuse?

-Removed R1 and R11 and measured 24.9V AC in their places. Fuse is good.
-Installed R1 and R11. Removed R2 and R12 and measured 33.5V DC in their places. Fuse is good.
-Installed R2 and R12. Removed U1 and U2. I then measured 33.43V DC across C2 and C5. Fuse is good.

Slightly excessive voltages, but it seems all is rather in margins.

So I'll be measuring resistance across C3 and C4 (capacitors) and then measuring resistance across D4 and D6 (diodes) and then C6 (capacitor?) I only need to test those two diodes?

The C3, R6, D4 are connected in parallel (as C6, R9, D6 too) then you have to measure the resistance only on one of the part in each half. It should be in range of 1k. If it is significantly lower - then it should be problems with corresponding half parts or maybe some PCB traces are connected together by solder bridge, metall crumb or so...
Take into account - in the process of measuring you have to wait some time while charging the capacitors to get real readings.
One more, just in case - check please  D1 and D8 while there are not U1 and U2. In one direction they should have low resistance, in another - high.

When I replace U1 and U2 where do I measure to see if they are working ok? Also, when you say to install them one at a time would that mean Install U1 take a measurement then remove U1. Install U2, take a measurement then remove U2.
Or does it mean install U1 and take a measurement and then install U2 and take a measurement?

Replace U1, measure the result on the first output (TP1-TP5). If all work OK - put U2 (the U1 stays in place). Measure the result on the second output (TP10-TP7).

[addaz]

Have you tried to power on full device with the fuse?Slightly excessive voltages, but it seems all is rather in margins...Replace U1, measure the result on the first output (TP1-TP5). If all work OK - put U2 (the U1 stays in place). Measure the result on the second output (TP10-TP7).

By full device do you mean power supply and preamp? If so then no, I've only tried powering on the power supply by itself.

U1 and U2 got shipped in static-free bags. Although I've never had a problem with static damaging a component before, should I be wearing a grounding bracelet when handling them? I bought a 7x lighted magnifier last night and could not find any solder bridges or connected traces.

As soon as I return home from work I'll post my numbers.

[hagtech]

It looks like it was built right.  I don't see anything obvious.

jh

[addaz]

More numbers:

I measure 1k on the C3, R6, D4 network.

I measured 1k on the C6, R9, D6 network.

Both D1 and D8 over-ranged my meter in one direction and measured 0 ohms in the other.

With U1 in place I measure 14.98V on TP1 and TP5.

With U2 in place I measured 14.92V on TP10 and TP7.

No fuses have blown so far.

I guess that means it works now!

Because every resistor, capacitor and diode measured as it should have, did removing U1 and U2 maybe "reset" something in circuit? I'm completely perplexed by this whole situation and frankly, I'm scared of installing the brand new blue LED I bought for this circuit. 

Currently I'm letting it sit and stabilize taking measurements every fifteen minutes. Should I keep the 250mA slow blow fuse in there?

[poty]

With U1 in place I measure 14.98V on TP1 and TP5. With U2 in place I measured 14.92V on TP10 and TP7. No fuses have blown so far. I guess that means it works now!

I hope so.

Because every resistor, capacitor and diode measured as it should have, did removing U1 and U2 maybe "reset" something in circuit?

Definitely - no!

I'm completely perplexed by this whole situation and frankly, I'm scared of installing the brand new blue LED I bought for this circuit.  Should I keep the 250mA slow blow fuse in there?

There are two possibilities:
1. Resolding parts deletes a solder bridge somewhere.
2. The fuses were either not slow-blow, or overrated. With full load on 115V the device should draw near 40mA. At the start time it may be 2-4 times more. It is possible that "slowness" of the fuses was not enough to sustain the inrush current.

I recommend to leave the 250mA fuse and start to use the device for something whether you think about (including testing LEDs).

[addaz]

With full load on 115V the device should draw near 40mA. At the start time it may be 2-4 times more. It is possible that "slowness" of the fuses was not enough to sustain the inrush current.

Interesting point. I checked my AC voltage at the transformer inputs and it measured at 121V. I can't do the math but maybe it was drawing too much.

Thanks, Poty for all your help. I couldn't have done it without you. 

I'll clean the PCB with some alcohol and place an order for a nice enclosure now. Hopefully I'll never need to return to this topic!

[poty]

I checked my AC voltage at the transformer inputs and it measured at 121V. I can't do the math but maybe it was drawing too much.

All the matches are easy.
We have TE70023 transformer, aspect ratio of the single secondary winding in 115V connection (according to the datasheet) is 21.3V/115V = 0.1852, number of windings - 2, efficiency - 68%.
According to the Bugle power supply datasheet: full load is 2x15V @ 0.1A. On the output circuit we can find two bleeding resistors (R6, R9) drawing additional 2x (15V / 1000Ohm = 0.015A). Just before the regulators we can find another pair of such resistors (R5, R8) and marked voltages on them. They are drawing: 2x (20V / 10000Ohm = 0.002A). Until this point we have current 0.1A+0.015A+0.002A = 0.117A. There are two more just across the secondaries. The voltage across them could be counted as 21V + 0.117A*1Ohm=21.117V (because some voltage is across R1 and R11), and current as 2x (21.117V / 1000Ohm = 0.021). Total current from the transformer is 0.117A + 0.021A = 0.138A RMS.
The current on the primary windings would be 0.138A * 2 windings * 0.1852 = 0.051A = 51mA. There is question about efficiency though, because some current would be additionaly drawn to heat the transformer. The lost would be less than 100%-68%=32%, because we use not full sinusoudal period, but pulse current. Approximately it should be around 25%, so the resulting primary current should be 51mA / 0.75 = 68mA.

When your voltage is more than 115V (say 121V) we should add (121V/115V)*100%-100%= 5,22% to all voltages that are not regulated. So, the resulting secondary current would be:
0.1A + 0.015A + (0.002A * 1.0522) + (0.021A * 1.0522) = 0.139A RMS. Primary winding current should be then: 0.139A * 2 * 0.1852 / 0.75 = 68.6mA. Not very much of overhead!

I hope all has been counted right. Not very much time just now to check.

My conclusion: 63mA fuse is for 230V usage.

[addaz]

I finished my power supply and wired it to the Bugle today. It sounds great. About ten minutes into an LP I started checking for hot components. U1 and U2's heatsinks were hot (U1 especially). They weren't unbearably hot, but they were hot enough to make me suspicious. The transformer was slightly warm but nothing to be concerned about. I then noticed that R4 and R7 were very hot to the touch. I couldn't keep my finger on them for more than two seconds.

I played albums for over an hour with no problems but I feel like the resistors shouldn't be getting that hot. Am I being paranoid, or should I let it be? After blowing all those fuses I'm really nervous about everything.

Here's how it looks:



By the way, I'm still using the 250 mA slow-blow fuse. I am not using an LED. My heatsinks are slightly different than the ones called for: they don't have the solder pins to mount them directly to the board. The washers I had under them kept slipping so the sinks are floating just above the board.

[addaz]

It seems that I have the exact same problem (almost verbatim) as this fellow: http://www.audiocircle.com/index.php?topic=88485.0
I'm using the 18v transformer and also using replacement regulators (per jim's replacement sheet.) However, that topic died off with no resolve so I'm wondering if there's an issue with the value of R4 and R7 and the 18v transformer?

Here are my numbers on those resistors:

R4 and R7 are 1k. I measured 23.5vAC across each resistor. That means that I have 0.0235 amps and 0.55225 watts across each resistor.

[poty]

It seems that I have the exact same problem (almost verbatim) as this fellow: http://www.audiocircle.com/index.php?topic=88485.0
I'm using the 18v transformer and also using replacement regulators (per jim's replacement sheet.) However, that topic died off with no resolve so I'm wondering if there's an issue with the value of R4 and R7 and the 18v transformer?

Could you tell us exactly - what changes you've made in the parts list?
18V vs 15V transformer couldn't have such dramatic effect. Your measurements:

R4 and R7 are 1k. I measured 23.5vAC across each resistor. That means that I have 0.0235 amps and 0.55225 watts across each resistor.

prove that the problem is not here. Looking at the photo of the board I realised, that you have rather small (in size) resistors on most positions, including R4, R7). Are they really 1W? Maybe they are rated at 1W in some circumstances only (like leads length or something). It may be possible that they can heat at high temperature without damaging too.

[addaz]

Hi, poty. I just double checked my DigiKey order and all the resistors I ordered are all metal oxide rated at 1W. However, now that I'm reading the fine print in the data sheet it says not to brush the resistors when cleaning as it may damage the coating. I definitely brushed them with alcohol during the cleaning process.

I'm also reading 29 volts across the large caps which are rated for 25v.

Here is the datasheet for the exact resistor I ordered: http://industrial.panasonic.com/www-cgi/jvcr13pz.cgi?E+PZ+3+AOA0018+ERG1SJ102+7+WW
I've looked over it and I can't find any info on wattage rating applied to leads. Maybe this needs to go in to Jim.

[poty]

Hi, poty. I just double checked my DigiKey order and all the resistors I ordered are all metal oxide rated at 1W.

DigiKey may send you wrong resistors. Lets assume you have correct resistors.

... the fine print in the data sheet .. says not to brush the resistors when cleaning as it may damage the coating. I definitely brushed them with alcohol during the cleaning process.

I doubt it matters...

datasheet ... ERG1SJ102...

According to the datasheet the external temperature of the resistors with applied power more than 50% is above 70 grad. C. It is rather hot to touch. There are no advises about leads length of the plain leads resistors, but other types show that they are 4 mm above the surface. I think it prevents damaging the surface by excessive heat, but it is only my guess. In your case I'd either use 2W resistors (just in case) or use bigger values (say 1k5).

I'm also reading 29 volts across the large caps which are rated for 25v.

Where exactly have you measured the voltage? Have you applied any load during the measurement? You can use any diodes instead of the serial resistors up to the regulators to drop 0.7-0.8V on each diode if you readings with the load exceeds 25V on each capacitor (not serially connected). They are cheap.

[addaz]

Hi poty. After some searching on Digikey I found what appears to be two drop in replacement for the 15v transformer that was originally called for. I ran the specs by Jim and he agreed so I ordered one last night.

For those who are interested the transformer I ordered is Digikey part number TE2241. It is a 7VA, 15v transformer that is 74% efficient and uses a 63mA fuse.

There is also TE2236. It is a 5VA version that is 68% efficient and uses a 50mA fuse.

Rather than fight a transformer that will always run hot I can now return everything to stock values and use the power supply as intended.

As soon as I get it soldered in I will get back to this post.

[poty]

For me - the decision is rather expensive for the nature of the problem, but if you are happy with it - then all is OK.