B2 burning fuses (F203-F204)

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dsmart705

Well-Known Member
My beloved B2 is once again down for an unknown issue. Afew weeks ago the unit went silent, I immediately shut it down for evaluation and found the F203 was open. The fuse was the original and it looked to me more like if cracked than "blew" so I changed it and all was well. Yesterday she went silent on me again, and sure enough F203 was open again as well as F204. My power supply board has be mostly overhauled but does still have the original diodes including the rectifier (D209). I haven't gone any further with this yet and fingers are crossed that there is no collateral damage but I was hoping for alittle direction from those who have been through this before. I did find this thread which seems similar with the exception that the source of my problem will not be a backwards cap. Cheers

B2 Fuses on PSB Keep Blowing after Refurb

After completing a complete refurb of my B2, the two right 500ma fuses on the PSB keep blowing when I power the unit up. The parts I replaced are all well documented in previous B2 refurb threads on this form. B2 was running fine before I installed the new parts which included the following...
audiokarma.org
 
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F203 and 204 is the 12v supply for the protect circuit and meter amplifier board.
 
dsmart705 said:
My beloved B2 is once again down for an unknown issue. Afew weeks ago the unit went silent, I immediately shut it down for evaluation and found the F203 was open. The fuse was the original and it looked to me more like if cracked than "blew" so I changed it and all was well. Yesterday she went silent on me again, and sure enough F203 was open again as well as F204. My power supply board has be mostly overhauled but does still have the original diodes including the rectifier (D209). I haven't gone any further with this yet and fingers are crossed that there is no collateral damage but I was hoping for alittle direction from those who have been through this before. I did find this thread which seems similar with the exception that the source of my problem will not be a backwards cap. Cheers

B2 Fuses on PSB Keep Blowing after Refurb

After completing a complete refurb of my B2, the two right 500ma fuses on the PSB keep blowing when I power the unit up. The parts I replaced are all well documented in previous B2 refurb threads on this form. B2 was running fine before I installed the new parts which included the following...
audiokarma.org
Click to expand...
What are you using for vu-meter lights?

You have vumeter lightbulbs, relays and the relay time delay circuit on that 12v (11.6v) rail. Nothing here should cause an issue with the vfets, but it would be safe to pull them until that PSU is solid.

Also, are you using a new selector for this B-2? If yes, you are also feeding a few mA to those selector relays. That load will vary from zero to about ~50mA depending on the use.
 
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rottalpha said:
What are you using for vu-meter lights?

You have vumeter lightbulbs, relays and the relay time delay circuit on that 12v (11.6v) rail. Nothing here should cause an issue with the vfets, but it would be safe to pull them until that PSU is solid.

Also, are you using a new selector for this B-2? If yes, you are also feeding a few mA to those selector relays. That load will vary from zero to about ~50mA depending on the use.
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I am using some original style bulbs (slighty brighter I think) that I bought from DJwojo. I am using one of your selector boards but both the bulbs and board have been installed in the B2 for quite some time without issue. When the first fuse blew I hypothesised it was just a one off event due to the age of the fuse. My plan is to have a closer look today and see if I can find something to report.
 
rottalpha said:
What are you using for vu-meter lights?
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Yes indeed!
dsmart705 said:
I am using some original style bulbs (slighty brighter I think).
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Just saying. For one of the recons I did years ago I accidentally replaced the bulbs with what was supposed to be OEMs (12V 60mA) I found on line.

NOT FROM DJwojo.

About 6 weeks after I returned it to the owner he called me to report that F204 blew; at the time I had no idea that the bulbs I bought weren't as advertised. :yikes:

After a bunch of head scratching I decided to measure the current draw on the extra bulbs I bought and sure enough, they each sucked about 20 more mA than the OEMs.
I'm thinking that after multiple power ups, the fuses fatigue due to the extra higher inrush current caused by the cold bulbs ... but of course YMMV.

An easy test would be to pull 1 of the leads at the Lamp Board and see if F203/204 still blows. :idea:
 
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I removed afew related components on the PSU and they all tested good. There are very few original transistors on there, I have changed all but (TR13,TR14,TR16). I checked my records and the bulbs the I had purchased from DJwojo were 14v 80mA. Instead of testing the bulbs individually I decided to test the whole string (as Vint Age suggested) by putting the meter in series. Im not too sure what to make of the results but the most current draw I could get was around 55mA at its peak which settled down to less than half that after afew seconds. I would have expected to see much more than that considering all 4 lights were on.....? The amp comes on normally and didn't blow any fuses right away but I only left it on for 3-4 minutes before terminating the test.
David
 
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The SM lists the bulbs as 12 volt 60 mA. Not sure how much stress that would put on the 12 volt rail.

On the switch board, did you run the GND wire properly? I wonder if that could cause the issue?

@rottalpha ?

Athanasios
 
Nashou66 said:
The SM lists the bulbs as 12 volt 60 mA. Not sure how much stress that would put on the 12 volt rail.

On the switch board, did you run the GND wire properly? I wonder if that could cause the issue?

@rottalpha ?

Athanasios
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It's possible that the higher current draw of the bulbs are the source of the issue but they have been installed in this particular unit for the better part of 2 years without any issues so i'm not sure why they would suddenly be a problem. The selector switch assembly has been in the amp for well over a year now and has also functioned without issue.

I will have to do more testing on this, my initial current test has lead to more questions than answers.
 
dsmart705 said:
I removed afew related components on the PSU and they all tested good. There are very few original transistors on there, I have changed all but (TR13,TR14,TR16). I checked my records and the bulbs the I had purchased from DJwojo were 14v 80mA. Instead of testing the bulbs individually I decided to test the whole string (as Vint Age suggested) by putting the meter in series. Im not too sure what to make of the results but the most current draw I could get was around 55mA at its peak which settled down to less than half that after afew seconds. I would have expected to see much more than that considering all 4 lights were on.....? The amp comes on normally and didn't blow any fuses right away but I only left it on for 3-4 minutes before terminating the test.
David
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Maybe put the amp meter in series right at the 12 volt fuse?

Not sure if that is recommended or safe but I think it give a better reading of whats going on right at the fuse itself.

Athanasios
 
Nashou66 said:
Not sure if that is recommended or safe but I think it give a better reading of whats going on right at the fuse itself.
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It would but before doing that I'd pull F201 and 202 and unsolder the red and white wires at the V-FET modules; once unsoldered make sure to insulate the wire ends for safety. The 12V DC should be pretty much isolated for further testing and the V-FETs will be unpowered and out of risk as well as the driver boards. :thumbsup:
 
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dsmart705 said:
I removed afew related components on the PSU and they all tested good. There are very few original transistors on there, I have changed all but (TR13,TR14,TR16). I checked my records and the bulbs the I had purchased from DJwojo were 14v 80mA. Instead of testing the bulbs individually I decided to test the whole string (as Vint Age suggested) by putting the meter in series. Im not too sure what to make of the results but the most current draw I could get was around 55mA at its peak which settled down to less than half that after afew seconds. I would have expected to see much more than that considering all 4 lights were on.....? The amp comes on normally and didn't blow any fuses right away but I only left it on for 3-4 minutes before terminating the test.
David
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replace with correct parts.
If DJwojo does not have them, you can find them in other places.
You need 12v @60mA 4mm dia. There are some on the auction site. I prefer buying from the seller in Germany. I bought others but those seem to be of good quality.
 
I have become busy with other things over the past few weeks and have just got around to doing more testing on my B2. I pulled F203 and tested the current flowing through that entire circuit which seems to stay steady around 465mA.....fairly close to the 500mA rated fues im using. My thinking is the bulbs are pulling more current than this circuit allows for (not much room to play with apparently!). From what I see here I have 2 options

1. keep the bulbs I currently have and move to a 750mA fuse
2. locate a set of original spec bulbs and keep the 500mA fuse

As temping as it is to just go buy afew fuses im sure the collective wisdom here would be to go with the bulbs.
 
Did you test the last bulbs outside the circuit to isolate their consumption … or the rest of the circuit without the bulbs…to make sure it is the bulbs alone causing the issue?
 
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Yes sorry I didn't include that information in my post, with the lamps disabled the current draw is 155mA. With 4 x 80mA bulbs in there the math checks out and it puts the total draw almost at the fuse rating. I don't know if 155mA is the proper spec for the rest of the circuit (minus the lamps) but it seems reasonable to me so I can only assume that my issue here is related to the bulbs. When the new ones come in i'll run afew more tests to confirm. When I bought the higher current bulbs afew years ago I did not consider how little headroom there is in that circuit.
 
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