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Build help and troubleshooting => CP4500 Stereo Bus Compressor => Topic started by: KJ on November 20, 2021, 09:42:07 AM

Title: VU Meter Jumps to 5 when there is power to my lunchbox, weird board measurements
Post by: KJ on November 20, 2021, 09:42:07 AM

Hello,

I am having a bit of a weird issue, i was trying to re measure and troubleshoot my CP4500 when I noticed it started this weird behavior with the meter sticking to 5, until the power is taken out from the unit or case. 

I still took some measurements up until step 4 which were looking good right before the VU started sticking around the 5 position, now all of the measurements from TP1-12 are wrong 

Can you help guide me as to what i should look at here? 

Channel 1

Step.....	Conditions	Result
1	Mix = 100% Ratio = 10 Attack = 0.1 Release =1.2 IN button pressed HF lift, 100Hz, 50Hz buttons released Negative meter probe on 0V	V+ =+15 to +16VDC, 0.73 VDC V-  =-15 to -16VDC) ,-15.97 VDC +12V = +11.1 to +12.9VDC,??? -12V  = -11.1 to -12.9VDC -11.78 VDC
2	Step 1 conditions plus: Input signal = 0V Threshold on +15 Makeup on 0	TP1, TP2, TP3, TP4, TP11, TP12 = 0VDC TP1: 2.27VDC  TP2: 1.28VDC Tp3 1.52 VDC TP4 1.39 VDC TP11 1.50 VDC TP12 1.50 VDC
3	Step 1 conditions plus: Input signal = 0V Threshold on +15 Rotate Makeup from 0 to +20	TP12 goes from 0 to -2.3VDC 1.50 - 1.50
4	Input signal = 0V Makeup on 0 Rotate Threshold from -15 to +15	TP13 goes from -1.8V to +2.8VDC 1.07 -1.50

Thank you for your help 

Title: Re: VU Meter Jumps to 5 when there is power to my lunchbox, weird board measurements
Post by: JPK on November 20, 2021, 05:53:15 PM

• V+ =+15 to +16VDC, 0.73 VDC

This is the first issue to take care of.
Remove all the IC's and check again.
The + rail comes through R41. Check if it is present on both sides.

Title: Re: VU Meter Jumps to 5 when there is power to my lunchbox, weird board measurements
Post by: KJ on November 20, 2021, 06:42:12 PM

Hi 

With all ICs removed 

the V+ is actually reading: -0.433 VDC
At R41: Side closer to the case connection pins: +16.8 VDC other lead of the resistor: -0.433 VDC

I then reflowed the solder points of R41, 

After reflowing R41: 

V+: -0.639 VDC
R41: -0.639 VDC on the board side, and on the side close to the connector: 16.13 VDC

what should I try next? 

Thank you, 
KJ

Title: Re: VU Meter Jumps to 5 when there is power to my lunchbox, weird board measurements
Post by: JPK on November 22, 2021, 09:58:12 AM

Check the resistor (in circuit) with an ohmmeter : 1 ohm.
It looks destroyed. It means there is a short circuit somewhere on the board that caused the destruction.
Check the short with the ohmmeter, between V+ and 0V.
Unplug from the front PCB and check again.
Remove all the IC's and check again.