Author Topic: EQ573 V1 - 10k Mid Bell Issue

April 25, 2021, 10:24:58 pm
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rasalrew

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Hey All,

I have an EQ573 that I purchased from somebody a few months ago. Upon purchase they let me know that the 10k switch on mid bell frequency didn't work. When they tried to fix it, It ended up messing up another frequency, so they decided to leave it as is. I don't know what other frequency it ended up 'messing up. I believe all other frequencies/bells/shelving/and knobs /switches function. However, I will note I can barely tell a difference between the HI Q (up position) and the 73 (down position). If there is a difference it is very subtle. The middle position is where I  can hear the most difference.

The 10k Is not that big of a deal for me, but I would like to fix it on the off chance I need to use that frequency or decide to sell the unit later on, as a fully functioning unit.  I've built a few kits before and get by with some basic troubleshooting, but I do not have a lot of experience reading/deciphering schematics. Besides reading the values of Resistor/capacitors before they're stuffed onto the board, My use with a DMM is limited. I'm going to re-visit the EQ with some info here on these forums but wanted to get any feedback possible.

I've reflowed solder and I checked connections at C51 (1.16nf), the Pin connections 10 rows down from top to bottom, and reflowed solder for all the Pins / Resistors around SW4.  When the 10k switch on the mid bell frequency is engaged I get a signal passing through, unaffected, basically the same as if it was in the "off" position. When 10k is selected and the gain knob is moved there are no changes. I haven't removed the front faceplate as I was able to reach all the connections with the soldering iron, but that may be my next step, maybe there is something I'm missing there. Any info/direction would help.


April 26, 2021, 11:12:37 am
Reply #1

JPK

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With the frequency switch set to 10kHz, check continuity with your DMM, between P3 center pin and C50 left hole.
If disconnected, the issue may come for a bad solder joint on the connector between boards, 10th pin down as you said, on both PCB's, on C51 and on SW4.
If connected, check you have a connection between the right pins of C51 and C53.
JPK

May 03, 2021, 12:40:20 am
Reply #2

rasalrew

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Ok, so I checked continuity 

C50
 left hole and Middle pin of P3. No continuity.

Right Pins C53  C51 Contuinity

Pin connectors  row 10 right pin on Main PCB had contuinty to C50 left hole.
Pin connectors  row 10 left pin on Switch Board had contuinty to C50 left hole.


bad rotary switch? Anything else I could check ?


May 03, 2021, 11:15:55 am
Reply #3

JPK

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It could be the rotary switch. You can test it with your DMM. The common contact is a pin situated inside the circle made by the 12 contacts.
JPK

May 03, 2021, 04:49:15 pm
Reply #4

rasalrew

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with the mid bell freq position set to 10k: to check continuity, it would be the center interior pin to C50 Left hole?

Continuity between  P3 middle pin and the interior center pin
No continuity between C50 left hole and the interior center Pin.

click to photo to enlarge


thank you for your help and patience
« Last Edit: May 03, 2021, 05:08:57 pm by rasalrew »

May 05, 2021, 10:01:28 am
Reply #5

JPK

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Quote
Continuity between  P3 middle pin and the interior center pin

OK good.

Check the continuity between the center pin and the 10kHz pin (circled yellow).
If there is no then the issue is the switch.
JPK

May 05, 2021, 10:52:03 am
Reply #6

rasalrew

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Just checked there IS continuity between center and the circle pin 10k. I will plug in the module and pass audio through in the morning to check to see if for some miracle it has started working, EDIT: but not continuity between C50 and P3 still so I assume the problem still persists. Any further steps?
« Last Edit: May 05, 2021, 11:06:42 am by rasalrew »

May 05, 2021, 02:49:25 pm
Reply #7

JPK

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The necessary connections for the 10kHz are:
P3-center pin to SW4-center pin,
SW4-center pin to SW4-pin#12 (circled yellow)
SW4-pin#12 (circled yellow) to C50/C51-left pin,
C50/C51-right pin to inductor L1-middle pin of a group of 3 in the bottom right corner.
JPK

May 05, 2021, 06:20:33 pm
Reply #8

rasalrew

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The necessary connections for the 10kHz are:
P3-center pin to SW4-center pin, Continuity
SW4-center pin to SW4-pin#12 (circled yellow) Continuity
SW4-pin#12 (circled yellow) to C50/C51-left pin, No Continuity
C50/C51-right pin to inductor L1-middle pin of a group of 3 in the bottom right corner. Continuity




ok so it must be the rotary switch. im assuming replacing it requires the switch board to be removed from the main board, quite a daunting task, can i email you about replacement parts?
« Last Edit: May 05, 2021, 06:24:12 pm by rasalrew »

May 05, 2021, 06:32:48 pm
Reply #9

JPK

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Quote
SW4-pin#12 (circled yellow) to C50/C51-left pin, No Continuity
This not the switch.

It is the connection from the switch pin (yellow circle) to the pin header (10th down).
Maybe a damaged track. You could try to restore it with a small isolated wire.


Quote
im assuming replacing it requires the switch board to be removed from the main board
No, we currently replace switches without separating the boards.



Quote
can i email you about replacement parts?
Sure.


JPK

May 07, 2021, 06:24:02 pm
Reply #10

rasalrew

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Perfect. Fixed! thank you

May 10, 2021, 05:27:44 pm
Reply #11

JPK

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JPK