[conorc]

Hi there, 
I’m wondering if i can use a capi ca-0252 or a gar 1731 in the 501? 
thanks!

[JPK]

Probably yes, as long as they do not output too much DC offset.
Check the DC volts on TP2. If it stays lower that a few millivolts then it's OK.

[conorc]

Great, thanks! 

I have another question. 

I finished the two 501s this evening and one seems to be working great (but need to take them in to the studio to check audio). The other one was fine initially and gave the correct + and - 16v readings on the test points, but my probe touched off something (possibly the mosfet?) and now the positive rail is down to a steady 0.7 volts and the DOA LED no longer illuminates. 

Do I need to replace Q1 maybe?

And if so, would this do the job?

https://www.newark.com/microchip/2n7000-g/mosfet-n-ch-60v-0-2a-to-92/dp/31AC2702?gclid=Cj0KCQjwyN-DBhCDARIsAFOELTkqyoyp0yevUdIfvNucXoHB6yvPcb0Kc78KrM68g0tM06Z3Sy4rm88aAhsgEALw_wcB&mckv=sV3NYpyb3_dc|pcrid|492622077317|plid||kword||match||slid||product|31AC2702|pgrid|108905520690|ptaid|pla-932219301484|&CMP=KNC-GUSA-GEN-Shopping-NewStructure-MPN-Semiconductors-Discretes#

Thanks!

[JPK]

A damaged Q1 could not put the +16V down.
Remove the DOA and check the +16V again.
If not the DOA, check the diode D1 (can be done in circuit).

[conorc]

Ah ok. I measured D1 and it gives a voltage drop of 0.563. D2 and D3 also seem normal. 
Thanks!

[conorc]

Removed the DOA and the + voltage is still down at -0.7


Also, I built 2 501s, so I checked the DOA in the other unit and it illuminates normally and the voltages at the test pins are normal in that unit with either of the 2 DOAs installed, so I don't think the DOA is the problem

[conorc]

Update: now both units have the same issue (the functioning one stopped working!), so I guess it must be a misplaced component as i built them side by side. Here are some images.

https://imgur.com/IGuXBTT
https://imgur.com/drFhves
https://imgur.com/dhbglzV

https://imgur.com/dhbglzVhttps://imgur.com/dhbglzVhttps://imgur.com/dhbglzV

[JPK]

Look for a reversed electrolytic, C10, C11, C14, C15 in particular.
Remove U1, the DOA and the front PCB and check the voltage rail again.
Check value of R21, R22, R23, direction of D3 and RLY1.

[conorc]

It looks to me like all of the resistors and EL caps are in the right place, but maybe you can see something in the pictures linked above?

I removed the opamp and pots panel, now the positive rail is zero (wandering up and down around 50mA to be precise).

Thanks!

[JPK]

Check the value and solder joints of R19. It is 1 ohms in series with the + rail.
Also check that the +16V rail comes through to the module. The issue could also be in the extender.

[conorc]

I checked the power headers of the extender, and they do indeed provide +16 and -16 as normal. 
 
Measuring R19 at the top leg of the resistor I get +16v and at the bottom leg of R19 I get -0.7v.

Keep in mind that both modules initially worked perfectly, and failed after a few minutes of being powered up. 

[JPK]

What value do you get when measuring R19 in circuit?

[conorc]

On one unit it's 0.38M, on the other I don't get anything (0.L on the DMM). That's with the units not powered up. Thanks!

[JPK]

on the other I don't get anything (0.L on the DMM).

This one looks damaged. Try replacing it.

[conorc]

Have ordered some replacement 1Rs (and some diodes and a couple of other parts just in case), will let you know!

[conorc]

Replaced the 1Rs and all is working perfectly 

There was no visible damage to them but maybe they were defective from the factory? Might be worth testing the remaining ones in stock....

[JPK]

Congratulations!
I checked some 1R0's from our stock randomly and they are all OK. Although rare, defective parts can occur.

[conorc]

Yeah who knows really! The EQs sound excellent. The multiple low frequency options really allow you to dial in a very solid kick sound, great for electronic stuff.

[conorc]

Hi there,
After a few months of use, one of my EQP 501s has developed a problem: the gain has lowered considerably, especially in the low end. You can see images from Room EQ wizard here where I compare it to my other unit which seems to be doing great: https://imgur.com/a/vgwcUQy The first images are of the unit with all gains down to zero, the second has them up to about 50% (and the low attenuation also at 50%). Any thoughts on what might be causing this? Thanks!

[conorc]

PS: I have swapped the DOAs with no difference in the results. Also, the tests were conducted using the same 500 slot and cables, so no variables there.

[JPK]

With all the gains at 0, does the low frequency attenuation changes when changing the low frequency CPS?
In sucha case it would suggest an issue with the low freq attenuation potentiometer.

[conorc]

I just tested it and yes, the CPS does change the frequency response when all gains are at zero. Here's images of the CPS at 15hz and 100hz: https://imgur.com/a/Fz0N3LB

If it is the low frequency pot that's the problem, what would you suggest to resolve it?

Thanks!

[JPK]

Can you check the P5 pot by measuring the resistance between the 2 extreme pins. It should vary from 0 to 100k.
If it doesn't you will need to replace the pot: Contact me by mail here.

[conorc]

I tested the pot and it actually seems fine: it moves smoothly from 0 all the way to the left to 10k all the way to the right. Anything else that might be a likely cause? Again, this unit has worked perfectly for 6 months before recently having this issue.
Thanks!

[JPK]

It must be the connections between the pot and the mainboard:
Check solder joints of:
- the pot,
- CN2A & CN2B the lower 2 pins, near the spacer.

You can check the continuity between the center pin of P5 and TP3 and C12 top pin.