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Disco Stu
Silver Member
USA
303 Posts |
 Posted - 09/28/2008 : 07:16:30
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Hello -
I've had this "Delay Champ" pedal for about twenty-five years. I plugged it into the wrong wall-wart a while back and it hasn't worked since. Looking around here, I see that this is a common problem.
The supply was not reverse polarity, but too many mA's. The pedal now allows tone through in "off" mode, but in "on" mode one can see the LED but only a very tiny fraction of sound comes through.
From reading other threads, I see that a common cause for this kind of problem is a protection diode gone bad... Hopefully that is my issue as it seems simple enough.
I did download the schematic from free information society page, but I'm not an EE and it's just a pretty picture to me.
If anyone has any tips, I would appreciate.
Thanks
Disco Stu |
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Dr. Bob
Moderator
Australia
6593 Posts |
Posted - 09/28/2008 : 11:25:01
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Hi Disco Stu
Upload some pics of your "Delay Champ" pedal.
Maybe we can help you out.
When you say wrong wall wart, do you actually mean it was a higher voltage than the recommended, rather than Higer mA?
The Higher current mA, would not have damaged it, but a higher voltage or AC rather than DC wall wart, would have made a big difference.
Please be more specific, it make a lot of difference, for us to know the actual details.
I am assuming that it also runs off a 9V DC?
Does it work from a Known god battery?
Does does the battery hot hot quickly?
Regards Dr. Bob
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MoonWatcher
Bronze Member
USA
98 Posts |
Posted - 09/28/2008 : 16:59:56
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Yeah - the most common oops that I've come across is an AC adapter subbed in.
The second most common is inverting the power supply - the diode may save the semiconductors, but I've seen instance where it doesn't.
The third most common is too much voltage which can fry chips if the voltage is above spec. Most op amps will handle upwards of 18VDC, but some will not.
If bypass is okay but "on" is not, you may have gotten lucky and just fried part of the "flip flop" circuit. Many pedals use a 4013 clock chip for the transition - that may have gone. But you shouldn't see the LED.
We really need a schematic if possible, and all specifics on the wall wart. Pics may yield no clues, if there's no visible damage, but if you can't find a schematic, it will have to do.
Since there are some signs of life, you can take heart! I've got a few old peds as well (ram's head muff that I recently re-enclosed), and this is an unfortunate part of dealing with them. |
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Dr. Bob
Moderator
Australia
6593 Posts |
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Disco Stu
Silver Member
USA
303 Posts |
Posted - 09/28/2008 : 21:40:47
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Thanks for your quick responses!
It has been a while since I applied the overzealous DC power transformer, so I will have to search around for the exact one for accurate data. What I recall, though, is that the mA rating was a much larger number than the 250 mA associated with a Boss ACA-120G adaptor... Possibly around 700 mA. Thinking back, it may have even been a 12V supply . The polarity as shown on the small diagram on the adaptor was correct (tip- ; shaft+). There were no burning odors.
The symptoms are as follows: when using a KGB (known good battery) or a correct adaptor (Boss ACA-120G), the LED lights up with a guitar cable in the input jack and the switch engaged. The delay effect comes through the amp with switch engaged and LED shining, but the sound is extremely muted even with the drive and gain knobs on the amp turned all the way up. With the switch disengaged, LED Off, again a tiny bit of sound comes through the amp.
If I switch the cable (from pedal to amp) to the "dry out" jack on the pedal, normal clean sound comes from the amp as if I plugged the guitar directly into the amp.
One other thing - when using the Boss power supply, no 9-volt battery attached, and the standard instrument->effect-> amp hookup, there is a noticeable hum from the speaker not present with a KGB as the power source. This happens both with the switch engaged or disengaged. The LED comes on with switch engaged, same as with a KGB as power source. The hum is a nice smooth-sounding midrange electrical hum.
Upon unscrewing the bottom plate and peeking at the circuit board, there are no obvious burnt or damaged components.
I can take a photo, but have not posted photos here as of yet so I am not sure if I can figure out how to do that. I will try posting a photo over in the "test" forum.
Thanks for your interest!
Disco Stu |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 09/28/2008 : 22:07:42
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G'day! Can you confirm the LED comes on at the normal strength when you turn the effect on?
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Disco Stu
Silver Member
USA
303 Posts |
Posted - 09/28/2008 : 22:20:35
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Hello Laurie --
Yes, the LED is a nice bright red both with a 9V battery or Boss adaptor.
I can tell you that this pedal always tended to eat up batteries voraciously, and the LED always dimmed noticeably as battery strength dwindled. |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 09/28/2008 : 22:54:22
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OK... because the LED is the right brightness and the on/off switching plus direct out work, we can eliminate the suspect of the reverse protection diode (D9).
The current capability of the adapter won't be a problem - you can run a 9V pedal off a 2000mA supply (or as big as you like, actually) - it will only draw as much as it needs. The excess voltage will be the culprit, and the problem is that the bigger the supply (in mA), the higher the unloaded voltage tends to be. I have a couple of 12VDC nominal power supplies that give out 18VDC unloaded.
The MN3102 clock driver has a maximum voltage rating of 10V. The MN3205 BBD has a maximum voltage rating of 11V. They receive power from a Zener diode (D3) - the schematic is a bit blurry, but I'm pretty certain that's the case.
I did the maths and if you applied 18V to the pedal (from a large 12VDC nominal supply like you used), it may well have burned out R54 (it is a 1/4W resistor with maybe 1W applied) - looking closely at R54 with a magnifier, is there any hint of brown/black from burning? It won't have been a slow burn, it would have gone fast so there won't be much damage around it. It may also have taken out D3.
The worst case scenario is if R54 is Ok and D3 is burned out (the MN3102 and MN3205 might be dead in this case). Best case is R54 burned out, D3 OK (replacing R54 should fix it in this case).
Do you have a multimeter? Can you check the voltage across D3 to confirm it is 8.2V ? With the power disconnected, can you check R54 is 100 Ohms?
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Edited by - Laurie on 09/28/2008 23:15:06 |
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Disco Stu
Silver Member
USA
303 Posts |
Posted - 09/28/2008 : 23:42:20
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Thanks Laurie --
Visually, I can't see any anomalies with R54 or D3; they appear the same as the other resistors and diodes: beige-colored resistors with lines of color to ID the vaues, and the diodes are red with a blue line. There are indeed several IC's as you described: one MN3205, one MN3102, also a "4558D JRC 7230" and the largest, sixteen-pin IC is labelled "NE571N KDV0591 8733KJ".
I can't see any signs of scorching on any components. I do indeed have a multimeter somewhere, and will find it and try to test the components you specified, and record the values.
Appreciate your help.
Disco Stu |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 09/28/2008 : 23:44:20
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OK... one of them still might be blown, but it might not be visible.
D3 voltage measurement is with the pedal turned on (PSA adapter connected and input lead plugged in).
R54 measurement is with the pedal disconnected from everything.
Let me know what you find...
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Edited by - Laurie on 09/28/2008 23:49:57 |
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MoonWatcher
Bronze Member
USA
98 Posts |
Posted - 09/29/2008 : 04:12:18
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quote:
Originally posted by LaurieCan you check the voltage across D3 to confirm it is 8.2V ?
Alternatively, does your meter allow you to test/measure diodes? This can be done with the pedal off.
A good meter and the pedal off may be your best bet - you can go thru the circuit and test them, starting around D3 and working your way "outward". Diodes can be measured for forward voltage, resistors can be measured to determine if you have an open circuit in one, as well.
You may not be able to get an accurate read on resistors that are paired up with capacitors (in parallel), but if you really suspect one of those, you could unsolder just one end to measure it.
Whilst one of the chips may be blown, chances are a resistor went first. If you find a bad one, it's a cheap enough sub before replacing any semiconductors. |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 09/29/2008 : 04:46:18
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| MoonWatcher is entirely correct. Test D3 with no voltage - that will tell half the story. Then test it with power applied - that will prove it is properly Zenering at 8.2V |
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Disco Stu
Silver Member
USA
303 Posts |
Posted - 09/29/2008 : 06:58:16
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Thanks Moonwatcher and Laurie --
Appreciate all of your input. I have to tell you all that I'm not an electrical engineer! The closest I've come is working in a microchip factory about fifteen years ago. We made four and six-inch wafers in a class 100 clean room.
So as far as testing diodes, I don't know where to start... maybe you could refer me to a thread here that explains the process? I am making a wild guess and thinking that I might choose a "DC Volts" setting on my cheapo Micronta "18-range Multitester" for checking diodes. Now resistors, I understand that I would need to switch to low range Ohms on the meter.
In regards to soldering and desoldering tiny components, I don't have the experience under my belt... I can sweat copper pipe and make leaded glass windows though! Before presuming to dissect a nice old pedal with sentimental value, I'd need to get some tiny soldering tips for my old Weller WLC-200 variable-temp station, figure out what type of flux to use, aquire soldering braid and PRACTICE for a few weeks on scrap pc boards from thrashed CD players and such.
So, I will try and explore the test procedures that you've outlined and let you know what data I can find. But I'm not prepared to stick a hot iron in there and ruin more stuff!
Thanks again for your advice.
Disco Stu |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 09/29/2008 : 14:28:16
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Shouldn't be any need to desolder for these tests.
Set you meter to DC volts (at a range around 10V or the next highest). Power up the pedal and measure the volts across D3. It should be 8.2VDC.
Power down the pedal, set the meter to "Ohms" (at a range around 100 Ohms or the next highest). Check R54 and see if it is 100 Ohms.
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 10/01/2008 : 14:54:02
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| G'day Disco Stu! Any updates on this repair? |
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Disco Stu
Silver Member
USA
303 Posts |
Posted - 10/02/2008 : 01:07:09
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Greetings !!
Finally found a functional multimeter. So here are the results...
I used a "Calterm Electronics" #66430 meter with LCD readout.
The new battery I put in the pedal reads 10.0 Volts on the meter.
Looking at the schematic, I see that R54, R58, and R67 are all called "22K" resistors.
Using the 20K setting on the meter and measuring across each resistor, I got readings of 19.45 or 19.25 for R54, depending on the orientation of the two probes. This was with no battery or other power source attached. I selected these three for comparison because they had the same color bands: red, red, orange, gold.
With battery attached, lead in jack and LED on, measuring across R54 read "-12.32" and each time I measured across R54 the LED went out.
R58 read 16.46 regardless of probe orientation.
R67 read 8.53 either way.
I got the same values whether I put the probes on the wires/solder joints on the bottom side of the PCB board or on the uninsulated part of the wires coming from the resistor on the top side of the PCB board
I measured D3 both with a brand new battery, and Boss ACA120G power transformer, without a battery attached.
With the battery I read 7.82 Volts. With the power supply I read 8.0 Volts.
That's all the data that I have for now.
Cheers! |
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Topic |
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Fried Ibanez CD-10 - any tips?
