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Unplug the two RCA connectors to the Reverb tank, and see if there is continuity on the input and output coils (va RCA jacks). Input would be around 70 ohms, output around 220 ohms DCR (not impedance). If either is open, look to see if there are broken lead wires between the RCA connectors and the tiny transformers (usually tiny IDC connectors. The wires break all the time on our rental gear.
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Logic is an organized way of going wrong with confidence -
I checked the RCA cables and they pass continuity a OK! I googled "DCR Ohms" and it still unclear how I measure this with my multimeter. Am i supposed to test the tank or the cables for the ohms specified above? I gave the tank a good shakingOriginally posted by nevetslab View Post
If the opamp is bad will that stop the reverb from working? I ordered a new one. Should be here in a few days.
As I was typing this I figured "why don't I just do the old finger on the tip test. When I touch black I get buzz. So I connect black to the out of the reverb tank. When i hit the reverb springs I get a popping sound and the faintest reverb springs. If I connect black to the input of the tank and jostle the springs I get reverb! Unfortunately I don't have another tank to test this with. Does this mean the output of the tank is bad?
SOmeone before wrote "r" next to the tanks output and "b" next to the input. If that means red and black then they swapped the colors used on the schematic. I wonder if it's possible someone disassembled the tank and maybe put it in backwards?
I also connected my phone via RCA to put input and output to see if could get audio to pass through and had no luck.Comment
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Whichever end of the RCA you touch. Red or Black. Amd can HEAR it thru the amp (reverb knob turned up) is the return.
DCR just means DC resistance. Or resistance. A.C. resistance is called impedance and is frequency dependent resistance. You're just seeing if you get a reading. If it's not OL on the meter and you get a reading, the transducer coil is ok.
Opamp voltages seem OK.Comment
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The way to test the input and output transducers is to read the resistance across the RCA jacks on the tank. If you don't get a resistance reading across either coil then check the small wires that connect the jack to the coil. There normally is a small nylon connector that pushes on to the transducer coil. The wires are fragile and break all the time.
By plugging in the tank and shaking it you have shown that the input coil and wires are okay, but the output side of the tank may be broken. This is where you need to check for broken wires or a bad coil.Comment
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If the wire on the output transducer wasn't broken before then i might have broken it when testing for continuity :embarrassed emoji: I didn't realize just how sensitive they were.
I see the service manual says the tank is a 4eb3c1b. I am going to buy this one now unless someone has a suggestion for a better replacement. https://www.ebay.com/itm/MOD-4EB3C1B...QQbYkKCten8-0g
Anyone have other ideas on how to get the drive channel going? Should I just hit all of the test points? I don't know where to look next.
Thank you all for your help so far. I really, really appreciate it. I have learned so much.Comment
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1 .02vOriginally posted by Fuzzy Slippers View Post
2 .02v
3 .01v
4 .002v <<<<< WRONG should be -16v
5 after r46 as indicated on the schematic .002v
6 .003v
7 -.001v
8 16.6v
I'm assuming the the duplicate pin 5 was a typo. Seems to me you still have a problem with the negative supply rail. Go and recheck R79.
Before buying a new reverb tank (1) measure the one you have and (2) Eliminate any other problems
Unless you gouge your probe into one of the coils of the reverb I don't think you will damage it. I have see the wires that go from the coils to the RCA's break. If they do they can be resoldered.
Find out what is up the the -16V rail first.Experience is something you get, just after you really needed it.Comment
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As he wasn't instructed to measure Pin 4, AND the numbers show nominal DC levels, we can assume the Neg voltage at the IC IS -16V.
Back to the DCR measurement on the Reverb Tank's Output coil....if that IS measuring open circuit, what I and most others do is cut the IDC connector off, strip & tin the two wires, tin the two tiny terminal posts of the output transformer, and carefully tack-solder the leads into place..noting the phase tht was there to start with. I only replace the tanks when the long coils springs have broken, or I have a bad input or output tank transformer. You could place 1/16" shrink tubing over the repaired solder joints. I find the wires break at both ends.
I've also had the molded REC cables to gad, but since you did get signal thru the Return path that end is at last good. joining the two RCA cables together, and barely cracking open the Reverb level, you should get signal from the Send circuit, proving that Reverb Input Tank cable is good.Logic is an organized way of going wrong with confidenceComment
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How about we measure pin 4, just for the fun of it?Experience is something you get, just after you really needed it.Comment
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correct: i did not measure pin 4 as i wanted to be respectful of the help every one has given me and follow directions as clearly as i can.Originally posted by nevetslab View Post
pin 4: -16v
touching the rca pins together gave me a very loud sound that had i held them together would likely have been identified as a feedback oscillation but i stopped after 200ms as my wife just put our 2 year old to bed and I suspect she's going to come down to the basement any second and scold me for making a sound so loud my left ear is now ringing. WOW that was loud. I had the reverb pot about half way up.
OK tried it again with the reverb off and slowly brought it up. It makes a squirrel like noise when touching tips.
I think it's very unlikely I will be able to reattach the wire I broke on the reverb. I've tried fixing an output transformer on an SM57 before and I just don't have the skill to be that still and careful.Comment
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Are the reverb tank transformers lacking dual pin connector headers, and the RCA connector wires NOT inserted into a plug-on mating 2-pin connector? If just direct-connected lead wires from the tiny transformer, then you're not going to have any luck restoring that output to the RCA jack. I haven't come across any tanks in the Hot Rod series that don't have a tiny connector plugged into the tiny transformer pins. We all repair these broken wires on a regular basis, and is always the first place we look when there's no Reverb function. On some of the newest reverb tanks from Belton, I find contact problems on the connector/pin interface, and have to clean them & exercise the connector a number of times.Logic is an organized way of going wrong with confidenceComment
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Thanks for checking. I needed to be sure since the symptoms no led, no master and no reverb are exactly what happens when you have no -16V and as far I could see it had never been tested at that point.Originally posted by Fuzzy Slippers View Post
It sounds like it was one of the fine wires on the coil that got damaged. Yes, they are tough and often impossible to fix.Experience is something you get, just after you really needed it.Comment
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thisOriginally posted by Fuzzy Slippers View Post
EDIT:I see it has already been checked ... I guess.Juan Manuel FaheyComment
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Concerning the channels. I just repaired one with channel switching issues with the help of Nickb. It ended up being U3 and possibly Q4 as well. But. I'd start first with listing all the TP readings that you get.Comment
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I bought a new tank. So we can consider the reverb issue on hold until it gets here. I am hoping it was just the tank.Originally posted by nevetslab View Post
I'll post my test point readings later today to try and figure out the drive channel.Comment
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reverb update: new reverb pan works! Thanks all. Still need to figure out the drive channel. Will try to get test readings for U3 and Q4 ASAP.
Does anyone want the broken reverb? Thing is shipping might cost about what a new does.Comment
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