Ibanez DE7 5v REG connects to ground through LED??

[gutsofgold]

I'm diagnosing an Ibanez DE-7 that passes dry signal only regardless of on/off state. I started my preliminary checks by measuring voltage at V+/V- pins of all ICs. I noticed that my 5V rail (coming off IC10 top of the schematic) is closer to 6.9V. This doesn't seem right as the circuit uses a lot of digital chips which rely on an accurate 5V rail... however if you notice there is an LED between GND pin of the regulator and circuit ground which could possibly raise the output of the regulator by the forward voltage drop of the LED which would be probably 1-2V. Should the high 5V line concern me or should I keep looking else where?

[gutsofgold]

Forgot the schematic 

http://www.ibanez.com/parts/2004_PARTS/electronics/tonelok/circuit%20diagram/DE7-01.pdf

[slacker]

Yeah the Led between the ground pin and ground will do exactly what you said, it will raise the output by whatever the forward Voltage of the LED is, so 6.9 Volts sounds correct. It looks like the power for the digital stuff goes through R3 and D3 to some filter caps and then some of it through D1, they presumably drop the Voltage down to what those chips want.

[PRR]

Does look like someone was confused. It does say "5V" yet the LED can't be a drawing-error and I expect 6.7V (6.9V no real difference).

> a lot of digital chips which rely on an accurate 5V rail...

I dunno. Most digital does not need an exact voltage, only that it be _steady_ and not far off.

Older CMOS all worked fine at 18V.

TTL is more fussy, but in small systems it can run on 4.2V, and (they won't admit this) it usually won't blow-up at 7V. (7.3V may be instant death.)

> power for the digital stuff goes through R3

Yeah, but 6.9V-5.0V drop in 22 ohms is 80-some mA, which is a LOT for a thing with a battery clip.

If you are still unsure, I see little harm in shorting that LED to get 5V.

[jealcori]

Hi everyone, I had the same problem currently I'm trying to repair a Ibanez DE7 the issue is the pedal only works with battery but doesn't work with AC adaper.

  I checked the regulator To92 is a NJU7200L33 ( and its a different semiconductor regulator from the NJM2930L05 that appear in the ibanez DE7 shcematics PDF, and on that schematics the ALTERA EPM3064 is not shown so my conclusion is the DE7 PDF is wrong).

 I changed the NJU7200L33 for a AMS1117 33 making pinout change to correspond with PCB and the DE7 pedal works OK but again only with battery, nothing with AC adapter, I have chek in both cases and the output voltaje is 3.3V.

  Does any one has the correct schematics?? Or any similar experience for ibaņez pedals working with battery but nothing with AC adapter??

  Thanks for your attention excuse my english I'm not english native.

[PRR]

https://www.diystompboxes.com/smfforum/index.php?topic=81651.msg1162760#msg1162760