91

MP573 Microphone preamplifier / Re: MP573 LED not behaving correctly

« Last post by JPK on August 15, 2025, 10:31:46 AM »

Is there a point replacing them if the readings are the same?
No.

With an input signal of 100mVAC, 1kHz, Gain=20dB, Trim=+10, Z=1200.
What AC voltage do you get on R50, against 0V ?
R50 left = 0.14VAC
R50 right = 0.57VAC

92

CP4500 Stereo Bus Compressor / Re: CP4500 Cannot level match and incorrect voltages in step 1.6

« Last post by JPK on August 15, 2025, 10:07:44 AM »

Both U6 and U7 get very hot!
No need to look further, they are dead. No IC should get warm in this design.

Misplacing a THAT1646 in a OP2134 spot kills it immediately.

93

MP573 Microphone preamplifier / Re: MP573 LED not behaving correctly

« Last post by davidfloegel on August 14, 2025, 07:55:37 PM »

Tested all of the diodes Diodes and compared them to my working unit - the readings are the same. Is there a point replacing them if the readings are the same?

94

MP573 Microphone preamplifier / Re: MP573 LED not behaving correctly

« Last post by JPK on August 14, 2025, 05:57:45 PM »

Compare the diode test of D6 with D7. Are they the same?
Try replacing D6.

95

EQP501 Passive Equalizer / Re: Son faible et pas d'EQ

« Last post by JPK on August 14, 2025, 05:54:06 PM »

Donc pas de -7.5V ?
Le Pb vient soit du commutateur SW3 (vérifier les soudures) soit des connecteurs CN1a/CN1b ou CN3a/CN3b.
Vous devez avoir la pin gauche de R21connectée au 0V lorsque le switch est sur une position ON.

96

CP4500 Stereo Bus Compressor / Re: CP4500 Cannot level match and incorrect voltages in step 1.6

« Last post by Gian on August 13, 2025, 12:15:19 PM »

Swapped U6 and U21 from the other board
So, I didn't blow up any chips, I disconnected power each time I took a new reading
Both U6 and U7 get very hot!

Step 1.6 compressor out
TP1=1.5VAC, 0VDC
TP2=0.245VAC but this value decreases as you hold probes
also checked DC volts on TP2=-12VDC
TP3=1.5VAC, 0VDC
TP4=57.8mVAC, 0VDC

U6 (gets hot and I disconnect power every 5 seconds, taking readings in each 5 seconds)
Pin1=0VDC, 0 VAC
Pin2=0VDC, 0 VAC
Pin3=0VDC, 0 VAC
Pin4=-16VDC, 0 VAC
Pin5=0VDC, 0 VAC
Pin6=0.437VDC, 0.370 VAC
Pin7=-8.18VDC, 8 VAC
Pin8=+16VDC, 0 VAC

C23-TP2 = -8VDC, 8VAC
C23-R55=-5VDC but drops quickly, 8.2VAC

U7 values(Gets very hot)
Pin1=0.228VDC, 0VAC
Pin2=3.68VDC, 0VAC
Pin3=0VDC, 0VAC
Pin4=3VDC but drops quickly, 8VAC
Pin5=-16VDC, 0VAC
Pin6=+16VDC, 0VAC
Pin7=3.675VDC, 0VAC
Pin8=-0.427VDC, 0VAC

Then I pulled out U6, U7 kept getting very hot
With U6 pulled out...
U6 values
TP1=0Vdc, 1.5Vac
TP2=1.26Vdc, 0.1Vac
TP3=0Vdc, 1.5Vac
TP4=0Vdc, 58mVac
TP11=0Vdc, 0Vac
TP12=0Vdc, 0Vac
TP13=2.8V(dc I think)

U6 (not inserted, but U7 inserted)
Pin1=0.63Vdc, 0Vac
Pin2=0.63Vdc, 54mVac
Pin3=0, 0
Pin4=-16Vdc, 0Vac
Pin5=0, 0
Pin6=1.25Vdc, 0.1Vac
Pin7=1.25Vdc, 0.1Vac
Pin8=+16VDc, 0Vac

Both U6 and U7 pulled out
U7 values
Pin1=0Vdc, 0.65Vac but keeps dropping
Pin2=0Vdc, 0.65Vac but keeps dropping
Pin3=0, 0
Pin4=-0.955Vdc, 0.1Vac
Pin5=-16Vdc, 0Vac
Pin6=+16Vdc, 0Vac
Pin7=0Vdc, 0.7Vac
Pin8=0VDc, 0.7Vac

97

MP573 Microphone preamplifier / Re: MP573 LED not behaving correctly

« Last post by davidfloegel on August 13, 2025, 11:22:56 AM »

U3 pin 1 : -1.31V...-2V  Doesn't seem correct.
Check the direction and solder joints of D6.
Check the solder joints of U3 pins 1, 2, 3.
Check D6 with the DMM.

checked solder joints - all good but resoldered anyways
direction of d6 - all good
value of D6 with DMM in diode test mode - 680

Retested values but Pin 1 still goes up and down in-between the previous volt ranges

98

EQP501 Passive Equalizer / Re: Son faible et pas d'EQ

« Last post by Pierro on August 13, 2025, 11:16:03 AM »

J'obtiens -15 sur le pin central, j'ai rechangé Q1 pour un neuf et toujours la meme chose, tension -15 et LED verte eteinte. Je l'ai manipulé avec precaution et en le testant apres l'avoir retiré il etait fonctionnel

99

CP4500 Stereo Bus Compressor / Re: CP4500 Cannot level match and incorrect voltages in step 1.6

« Last post by JPK on August 13, 2025, 10:32:53 AM »

Swap both U6 and U21 with 2 new OPA2134's.

100

EQP501 Passive Equalizer / Re: Son faible et pas d'EQ

« Last post by JPK on August 13, 2025, 10:30:33 AM »

Vérifiez que la tension de commande arrive bien sur le Gate du 2N7000 (pin centrale) : -15V=Off, -7.5V=On
Sinon, c'est le 2N7000 qui est HS. Attention c'est un composant très sensible à l'électricité statique. Il faut le manipuler avec le corps à la terre (c'est à dire sans chaussures).