41

CP554 Diode bridge compressor / Re: Cant get 3v at step 5

« Last post by vwyf11 on April 13, 2026, 08:30:35 PM »

As a last ditch effort I would guess, but would like to avoid sending it overseas if it’s possible.  

The voltage at the transformer was always the correct 24 volt reading before, now suddenly it’s 28.  I was atleast getting voltage between tp2 and tp3 now I’m suddenly seeing nothing.  Seems pretty drastic and like there should be something blatantly obvious.  I’ve looked at the schematic but it’s a little over my head with the amount of paths.  Is there a good straight shot to test voltage where the issue may be originating?  I obviously know I’m getting the correct voltage to the unit but having a tough time pinpointing the dc voltage path order.

42

CP5176 FET compressor / Re: 2nd CP 5176 Failed at TP3 Troubleshooting

« Last post by RFR on April 13, 2026, 07:57:28 PM »

Adding measuments from Trouble Shooting Guide

2.) 
V+: +15,9  VDC
V-: -15,93 VDC    
L1:  55    mVDC

No Signal
A: 12,8   VDC
B:  0,587 VDC
C: 13,41  VDC
D: -0,135 VDC
E: 15,14  VDC
F:  0,784 VDC
G: -15,16 VDC

3.) 
TP1: 538   mVAC
TP2:  7,26 VAC
L1:  10,9  VAC 1:2-1:20
     13,3  VAC @Slam

4.) 
TP3
1:2  = 0,178 VAC
1:4  = 0,353 VAC
1:8  = 0,570 VAC
1:12 = 0,950 VAC
1:20  = 1,62  VAC
Slam  = 7,18  VAC

TP4
1:2  =   0   VDC
1:4  =  -0,5 VDC
1:8  = -1,34 VDC
1:12 = -2,46 VDC
1:20 = -5,50 VDC
Slam = -0,64 VDC

JMP1 Pin 1
1:2  =  0,073 VDC
1:4  = -0,010 VDC
1:8  = -0,012 VDC
1:12 = -0,015 VDC
1:20 = -0,018 VDC
Slam =  8,860 VDC


TP6

-3,61 VDC

TP5
0,32 VDC

43

EQP501 Passive Equalizer / Re: Signal gain increase when engaged

« Last post by jziemba001 on April 13, 2026, 07:25:03 PM »

Hi,

I’m having a similar result, though maybe not as extreme.

When I send the unit a 0dBu (.775V) 1 kHz signal, I get the following reading from the output pins:
Bypass: .769V
Engaged: .852V

So if my math is correct, that’s roughly a ~ .89 dBu increase when the unit is engaged.

Following this thread, I’ve checked the following:

R5, R6, R7, R8, R12, R13, R25 all correct
R10, R24 correct

3V 1kHz signal
TP1: 2VAC (1.963)
TP3: 0.17VAC (.168)
TP2: 1.7VAC (1.731)

With the module unplugged, all pots at 0, 

- what resistance do you measure between TP1 and TP3 (?10k)? 
(9.87R)
- what resistance do you measure between TP1 and 0V (?11k)? 
(10.82K)
- what resistance do you measure between TP3 and 0V (?1k)? 
(.943K)

P3:
Can you measure it, between the 2 side pins, in circuit, after disconnecting the front PCB from the main PCB and with Low frequency ATTEN pot on 10 ? (9.87R)

I also checked all solder joints on all the potentiometers and they look good.

Is this less < 1 dBu increase in level I’m measuring at 1 kHz when engaging the unit considered normal behavior?  Or should I investigate anything?

Otherwise all functions seem to be operating normally, both with test audio signal generation (sine and white noise) and also musical material passing through it…and the unit sounds quite fantastic!

The small level bump is barely noticeable if at all when engaging and disengaging the unit with music playing through it.  Though I do here a small tick when it passes through the “off positions of the KCS switch, but I think this is normal as it is with most 500 series units since it uses an active relay?  The clicks are not present when switching without audio passing through.

I can send mdat files or screenshots of sweep measurements I took in REW with the unit in bypass and also engaged with all knobs set fully counter-clockwise if that's helpful.

Please let me know what you think!

Cheers,
Joe

44

MU524 Vari-Mu Tube Compressor / Re: Low output voltage step 6

« Last post by Ben on April 13, 2026, 06:58:31 PM »

I get 0mvAC across T1 pins 2-5
I get 67mvAC across T1 pins 7-10
power off 1vAC on input.

T1
pin 2-4   37.1 ohms
pin 2-5   37.3 ohms
pin 7-9   99.9 ohms
pin 8-10  100.6 ohms
input pin 2-3  14.14k ohms (this looks off)

Thank you

45

CP554 Diode bridge compressor / Re: Cant get 3v at step 5

« Last post by JPK on April 13, 2026, 03:40:21 PM »

Is it time to send it to our workshop for a check?

46

CP5176 FET compressor / 2nd CP 5176 Failed at TP3 Troubleshooting

« Last post by RFR on April 13, 2026, 12:30:02 PM »

Hi community,

I'm having an issue with my 2nd CP 5173 (#2).
I don't get the voltages at TP2 & TP3 compared to my 1st unit (#1).

Anything from 1:2 to 1:20 doesen't come close measurements.
Also I see a bigger gap on TP1 when I increase Source Voltage. Did I install T1 wrong? I'm sure I checked this 2 times prio soldering.

I can exclude front PCB, as I have the same results when using the front #2 at main #1 pcm.

Any idea why my Voltages are tht so far off?
Measurements:

47

MU524 Vari-Mu Tube Compressor / Re: Low output voltage step 6

« Last post by JPK on April 13, 2026, 11:33:34 AM »

With a 1VAC signal at the input, IN pot on 10, power off, how many millivolts AC do you get on the input transformer between pins 2 and 5?

48

CP554 Diode bridge compressor / Re: Cant get 3v at step 5

« Last post by vwyf11 on April 13, 2026, 04:34:21 AM »

I’ve replaced D20, Q7, U3, TR2.  Before replacing anything I checked between TP2 and TP3 and was getting 0.001V.  After replacing all the components listed, I’m getting the same values. 

Here are the values from the DC voltage checks in the link you gave from before:

A: 1.14V this value bounces around a lot
B: 0.561V
C: 0.525V this value bounces around a lot
D: 28.1V
E: 28.1V
F:0.001V

TP3 to 0V measure -12.8V

49

MU524 Vari-Mu Tube Compressor / Re: Low output voltage step 6

« Last post by Ben on April 11, 2026, 09:23:01 PM »

Apologies, my DMM lead must have had a bad connection testing TP2. I actually have 29.79vdc and 0.145vac @ TP2. TP3 is the same

50

MU524 Vari-Mu Tube Compressor / Re: Low output voltage step 6

« Last post by JPK on April 11, 2026, 06:49:12 PM »

TP2=  0.057 VDC
Here is the issue. You should get around 30VDC.
You must check the solder joints on R7, on the tube socket, on the connector that links the tube PCB to the main PCB.
Check that the 48V gets to both sides of R7 (you can check without the tube inserted).