EHX Holy Grail Classic (big box) - no reverb  [SOLVED]

Forum dedicated to helping people debug and troubleshoot non-functional pedals or builds. Please use an clear and informative title, indicating circuit and basic problem. Don't forget to mark the issue as fixed if this is the case.
Post Reply
User avatar
j_flanders
Information
Posts: 26
Joined: 14 Apr 2014, 13:10
Has thanked: 9 times
Been thanked: 18 times

Post by j_flanders »

This post is mostly for documentation purposes and for future reference.
Maybe it can help someone fix their broken Holy Grail.

I recently got a used, older big box Holy Grail (pointer knob, Rev A, non true bypass)
Though advertised as 'in good working order', there was very little reverb.
Only with the reverb knob at around 4 o' clock (close to 100% wet) I could hear a faint reverb signal. At that point the dry signal had lost more than 90% of its volume.

Being familiar with the circuit I knew there could be only 3 possible reasons for this behavior:

- dry signal going into the Crystal CS4811 reverb chip is too low
- wet signal coming out of the Crystal CS4811 reverb chip is too low
- wet signal coming out of the Butterworth filter after the Crystal CS4811 reverb chip (going into the blend circuit) is too low

Luckily I had another big box Holy Grail (hockey puck knob, true bypass Rev C).
After comparing the two pedals and taking voltage readings in appropriate places I quickly found the culprit: a faulty capacitor (C8) at the input of the reverb chip:
Image


I didn't remove the old faulty cap (for now) and simply added a new 10µF electrolytic cap in parallel.
End result: perfectly good working Holy Grail!
Image

Image

Image

Image

There are a lot of broken Holy Grails out there.
Most of them have a burnt R1 resistor or some wire that got loose.

Hopefully the fix above can bring the ones back to life that suffer from very low or no reverb levels.
Attachments
IMG_20210519_210137.jpg
IMG_20210519_204840.jpg
HG-faulty-cap.jpg

User avatar
joselima12
Information
Posts: 2
Joined: 06 Feb 2023, 22:22

Post by joselima12 »

Hey! How did you test each cap? I'm assuming testing them in the circuit won't work.

User avatar
j_flanders
Information
Posts: 26
Joined: 14 Apr 2014, 13:10
Has thanked: 9 times
Been thanked: 18 times

Post by j_flanders »

joselima12 wrote: 06 Feb 2023, 22:23 Hey! How did you test each cap? I'm assuming testing them in the circuit won't work.
I did test them in circuit.
Worst case scenario, you're reading additional caps in parallel.
The values of parallel capacitors add up.

If you measure a 10µF cap and it reads in the pF range, then you know there's something wrong with it. It should at least read around 10µF or higher, for potentially other caps in parallel.

Doesn't work the other way though: if you measure a 120pF cap and it reads in the µF range you can't tell if the pF cap is broken or if it's due to a µF cap in parallel.

In this circuit it's all electrolytic µF range caps that are potentially problematic.

Eventually I replaced the faulty electrolytic caps. (instead of tacking a new cap onto the faulty one, as shown in the first post)

In case you're trying to solve the infamous HG high pitch whining issue, this thread may be of interest:
https://www.google.com/search?q=666+hz+ ... Holy+Grail


Another

User avatar
joselima12
Information
Posts: 2
Joined: 06 Feb 2023, 22:22

Post by joselima12 »

Thank you for the help!

My HG has no wet signal, but dry signal passes no problem. Every cap I measure, however, is reading much lower than it should, or they reading as overload. Do you know that might cause this issue?

Thank you in advance!

User avatar
j_flanders
Information
Posts: 26
Joined: 14 Apr 2014, 13:10
Has thanked: 9 times
Been thanked: 18 times

Post by j_flanders »

joselima12 wrote: 09 Feb 2023, 21:48 Thank you for the help!

My HG has no wet signal, but dry signal passes no problem. Every cap I measure, however, is reading much lower than it should, or they reading as overload. Do you know that might cause this issue?

Thank you in advance!
It probably means those electrolytic caps have dried out and/or have leaked.
I'd start by replacing C8.
Here are 3 ways to remove electrolytic smd caps:
https://www.thegearpage.net/board/index ... t-35111466
(I used the technique shown in the second video.)

User avatar
chongwui
Information
Posts: 10
Joined: 27 Feb 2021, 16:02
Has thanked: 2 times
Been thanked: 2 times

Post by chongwui »

j_flanders wrote: 21 May 2021, 22:31 This post is mostly for documentation purposes and for future reference.
Maybe it can help someone fix their broken Holy Grail.

I recently got a used, older big box Holy Grail (pointer knob, Rev A, non true bypass)
Though advertised as 'in good working order', there was very little reverb.
Only with the reverb knob at around 4 o' clock (close to 100% wet) I could hear a faint reverb signal. At that point the dry signal had lost more than 90% of its volume.

Being familiar with the circuit I knew there could be only 3 possible reasons for this behavior:

- dry signal going into the Crystal CS4811 reverb chip is too low
- wet signal coming out of the Crystal CS4811 reverb chip is too low
- wet signal coming out of the Butterworth filter after the Crystal CS4811 reverb chip (going into the blend circuit) is too low

Luckily I had another big box Holy Grail (hockey puck knob, true bypass Rev C).
After comparing the two pedals and taking voltage readings in appropriate places I quickly found the culprit: a faulty capacitor (C8) at the input of the reverb chip:
Image


I didn't remove the old faulty cap (for now) and simply added a new 10µF electrolytic cap in parallel.
End result: perfectly good working Holy Grail!
Image

Image

Image

Image

There are a lot of broken Holy Grails out there.
Most of them have a burnt R1 resistor or some wire that got loose.

Hopefully the fix above can bring the ones back to life that suffer from very low or no reverb levels.
Thanks for sharing this info. I fixed my unit by replacing C8. I measured all the e.caps on board (in circuit using multimeter) and I am getting very low capacitance. I am planning to change all of them to through hole caps.

User avatar
j_flanders
Information
Posts: 26
Joined: 14 Apr 2014, 13:10
Has thanked: 9 times
Been thanked: 18 times

Post by j_flanders »

chongwui wrote: 21 Jul 2023, 22:14 Thanks for sharing this info. I fixed my unit by replacing C8.
That's great to hear. Thanks for posting.

Post Reply