Reverb weird problem on DRRI

[Guitardropper]

Hello to all!

I tried everything i could for the past one and a half week in order to solve this issue.

The issue:
The reverb on my DRRI suddenly stops working as i play. Upon closer inspection i found out that you can hardly hear (very faintly) the reverb sound, even with the reverb on 10, and that when i lightly tap the tank you can hear the springs. Weird thing is that when i close the amp (and let it rest for a minute or so, so the voltages drop) and open it again, the reverb is sometimes start working again, until after 5 minutes or after 1 hour it stops working again.

Things i tried and didn't work:

• Checked the tank for connectivity issues, and replace the tank with another i had laying around
• Checked the female chassis RCA reverb plugs - everything is ok
• Checked the cable itself - everything is ok
• Replaced the 12at7 type tube of the phase inventer with the 12at7 type tube of the reverb driver  - it made no difference on the reverb
• Replaced the 12ax7 type tube of the 2nd gain stage for ch2 and reverb with the 12ax7 type tube of the tremolo - it made no difference on the reverb

*I didn't have new tubes to test, so i though that by changing place of the tubes that are associated with the reverb to another socket (given the fact that it was the same tube type), i could maybe watch if i could spot any difference (i know that it may not be correct according to how the tube science/physics do their magic but i gave it a try anyway).
**By ''checked'' (rca plugs cable etch...) i mean really checked, with a multi-meter for connectivity issues, wiggle everything around trying to find if its a solid connection, inspected the solder joints for a bad one, and re-solder a connection that it remotely resembled something less than a ''pretty decent solder joint''.

Please let me know if i could provide any additional info that could help.

[mresistor]

If you have a set of common rca cables  like as used on stereo  you can substitute those instead of the original ones.
Is everything else in the amp working OK? And are you using a footswitch?

[sluckey]

What voltages do you measure on V3 and V4 pins 1, 2, 3, 6, 7, 8?

[Guitardropper]

What voltages do you measure on V3 and V4 pins 1, 2, 3, 6, 7, 8?

V3  1: 0.398v    2: -0.73v   3: 1.5mv  6: -399v   7: -0.75v  8: 1.5mv

V4  1: -0.42v    2: -0.31mv   3: 123mv  6: -0.41v   7: -0.45v  8: 123mv

[PRR]

Thanks.

> V3  1: 0.398v    2: -0.73v   3: 1.5mv  6: -399v   7: -0.75v  8: 1.5mv
> V4  1: -0.42v    2: -0.31mv   3: 123mv  6: -0.41v   7: -0.45v  8: 123mv

Not making sense yet. V3 p1 p6 should be tied together and the same voltage. You give voltages 1,000:1 different.

V4 p2 is a remarkable reading, since few affordable meters will read that small.

Which makes me wonder if your meter's "mV" symbol is not 'loud enough' to get your attention consistently.

We "expect" to find "about zero" on grids (p2 p7), "a few volts" on cathodes (p3 P8), and "hundreds of volts" on plates (p1 p6). The factory paper does not put all the clues together, so I annotated.

Since it is not working, probably some of your voltages are not what they "should" be. Now that you have the "right" answers, re-measure and be sure which ones are about right and which ones are clearly out of the ballpark.

[Guitardropper]

Thanks.

> V3  1: 0.398v    2: -0.73v   3: 1.5mv  6: -399v   7: -0.75v  8: 1.5mv
> V4  1: -0.42v    2: -0.31mv   3: 123mv  6: -0.41v   7: -0.45v  8: 123mv

Not making sense yet. V3 p1 p6 should be tied together and the same voltage. You give voltages 1,000:1 different.

V4 p2 is a remarkable reading, since few affordable meters will read that small.

Which makes me wonder if your meter's "mV" symbol is not 'loud enough' to get your attention consistently.

We "expect" to find "about zero" on grids (p2 p7), "a few volts" on cathodes (p3 P8), and "hundreds of volts" on plates (p1 p6). The factory paper does not put all the clues together, so I annotated.

Since it is not working, probably some of your voltages are not what they "should" be. Now that you have the "right" answers, re-measure and be sure which ones are about right and which ones are clearly out of the ballpark.

Thats really embarrassing...  

Yesterday it was my birthday and i came really late home and took the readings before i went to sleep...Sorry for this

the correct readings here (with the reverb working):
**As soon as i touched my multi meter to the first pin of V3 - reverb started to work
> V3  1: 423v    2: 7.7mv   3: 8v       6: 423v   7: 7.7mv  8: 8v
> V4  1: 208v    2: 0v         3:1.56v   6: 208v   7: 0v        8: 1.56v

I  closed and opened the amp and i had no reverb and i was about to take the reading (with the reverb not working) but it suddenly kicked in and start working again (i ll check all the solder connections to the tubes v3, v4 as well). And if i have no luck finding a bad connection i ll be watching so i can take readings when its not working.

P.S. multimeter is an extech 330 that i bought on sale for around 40 dollars - i dont know how good it is compared to better ones because its the best i own

[PRR]

That pin 1 is not soldered right. Clean it down to bare metal, tin lug and lead, solder neat so you can see the solder WETS both metals.

However, like mice in the attic, or deer in the road: if you have one bad solder joint you probably have more. (I nearly clocked a scrungy deer last week, and sure enough, there was an even scrungier deer lurking in the bush.)

[Guitardropper]

That pin 1 is not soldered right. Clean it down to bare metal, tin lug and lead, solder neat so you can see the solder WETS both metals.

However, like mice in the attic, or deer in the road: if you have one bad solder joint you probably have more. (I nearly clocked a scrungy deer last week, and sure enough, there was an even scrungier deer lurking in the bush.)

Today i found the time to play and after 20 minutes the reverb stopped and i took the opportunity to measure the voltages. No big difference.

> V3  1: 422v      2: 7.8mv   3: 8v       6: 422v      7: 7.8mv  8: 8v
> V4  1: 207.3v   2: 0v         3:1.56v   6: 207.3v   7: 0v        8: 1.56v

After that i tried to tap the solder joints on the tube sockets with a chopstick to see if i could find the one that had the problem but nothing changed, reverb still not working.

I ll do what you suggested and carefully re-solder the joints in v3 and v4 and i ll post an update.

[Guitardropper]

Guys i re-soldered everything in v3 and v4 from the pcb to the sockets and checked for continuity with the multi meter from under the tube socket to the pcb in order to be completely sure about it.

Note * : This was my first build , in which i used a DRRI fender pcb that was removed from a new DRRI amp (that had a turret board replacement) and build everything else around it (transformers, chassis, tube sockets etch.) and did some minor components changes ( replaced a few caps to my liking). So even if i am worried for a bad solder joint the majority of the components were already mounted, so that minimizes the possibility of an error in the main circuit due to my soldering skill.

So now that the voltages seem alright and all the joints from the pcb to the tubes and from the pcb to the tank (rca chassis mount, cable, tank) are double checked, what is the next step. Where do i have to look?

[vampwizzard]

Did you use a beeping continuity check? I like to check the overall resistance between my points.. a bad solder joint can show a slightly higher resistance than a good joint.

Id check my connections to ground as well. bad ground connections will lift whole sub circuits out and can be really tricky to hunt down.

[Williamblake]

You sure you still got a problem? Change tube again. Also chopstick soldering joints.

[Guitardropper]

Still got a problem. I even re-tensioned the tube sockets with a very small screwdriver. 

[Papa Jim]

Probably time to build a simple audio probe from a chopstick and resistor and when it stop pinpoint where the signal actually stops. Possibly an intermittent reverb transducer or iffy reverb cable.

[tubeswell]

I've repaired a number of DRRI amps where there were bad traces on the PCBs, by jumping the traces with conventional single strand insulated hookup wire. Use the R-meter to find the dud traces - these won't always be obvious from visual inspection. Expect the traces on those PCBs to go bad eventually. They are designed for the convenience of mass-production and become progressively less reliable over time. Reflowing solder on the trace pads sometimes works, but can be a bid hit and miss.


Also check and retention the tube socket pin clamps with a fine tip jewellers screwdriver or similar tool (with the amp off and the filter caps discharged) (Edit - Oops - you did that already)

[Guitardropper]

Guys thanks for your replies. Tomorrow i ll build an audio probe and i ll check for bad traces.

Could someone highlight the area on the schematic that i should check? ( edit : also uploaded what i think is the path of the reverb signal  and i think the problem should be in that area, let me know if i am wrong)

Also is it possible to be a bad transformer (edit: i just checked the transformer according to the image i found and my readings where blue/red: 1.04 kohm & black/green 1.2 ohm, and had no continuity in the other combinations)

or a bad tube (although i tried changing the place of the v3 and v4 tubes with the other tubes on the amp, but i have no new tubes to check)?

[shooter]

guessing you don't have a scope?
If you did, the lime circle shows 1.4mVAC, if you hum is = or > at that point the circuit could be completely fine and she'd still hum

the lime X's, cut there with no signal, still hum?

unplug tank, hunt up an mp3 player with volume, set to 0, get a 1/8 to rca adapter and jack in the player at reverb return, clean music?

[tubeswell]

i ll check for bad traces. Could someone highlight the area on the schematic that i should check?

Bad traces could be the ground return traces, (which aren't shown on the schematic). You have to check the laboriously old fashioned way, by carefully R-ing each trace, one at a time.

[Guitardropper]

guessing you don't have a scope?
If you did, the lime circle shows 1.4mVAC, if you hum is = or > at that point the circuit could be completely fine and she'd still hum

the lime X's, cut there with no signal, still hum?

unplug tank, hunt up an mp3 player with volume, set to 0, get a 1/8 to rca adapter and jack in the player at reverb return, clean music?

The problem is not that i have hum, the problem is that you can hear the reverb very very faintly, practically i have no hint of usable reverb even with the reverb knob at 10

[Papa Jim]

The connection between the small return and send wires to the actual transducer pins can often be faulty due to the insulation displacement type connectors that the tank mfg. sometime use. I would check that from the tanks send and return phono connections to the transducer pins with the small connectors slid back just enough to get your meter leads on. That way the wire to connector connection gets checked and not just the wire.

[shooter]

by putting the mp3 in the rev ret that "should" tell you the recovery 1/2 is working, or not.  shouldn't take but about 2 on the mp3 box to blast a hot signal

[Guitardropper]

Sorry to open this up again but I found the issue today and though that I should post in case someone finds it useful in the future! It was the stupid flex cable that fender used to connect the potentiometer pcb to the main board (in more detail it was the lug from the reverb pot to c17 that was broken) . The problem is that the 3 flex cables are not soldered in one end, so the leads inside are just pressed between 2 contacts that are then pressed against a pin protruding from the board  . That was the only original cabling I didn't replaced in the first place!

Thanks for all the help!

[sluckey]

Weird problems often have weird causes. Your perseverance paid off. Good job.