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vintage epiphone EBM-5 electronic question

L

lordraptor1

Dec 8, 2014
94
13
51
#1
ok I have a question regarding the electronics in my recently acquired epiphone EBM-5 5 string bass. basically I got it in non functioning condition ( no sound), so I went into the electronics cavity to check for bad caps. etc and went ahead and reflowed all the solder connections because they had that old crystalized look to them and poof I had sound. now the issue is the volume is extremely low. to actually be able to hear it decently ( although still not very loud at all) I am required to have all 4 knobs maxxed at 10.

now with the above said a little explanation of this setup, it is a p&j type with 1 volume knob and 3 other knobs which I can only guess as to their actual purpose but my best guess is the three other knobs are one of 2 setups:

1. low, mid, and high tone controls
or
2. pickup selector, and 2 tone control

the volume knob works like any other but the other 3 have a step in the middle ( think of a clock face with the dial rotting 1 to 12 with a spot at the 6 o'clock position).

ok now for the question anyone have any ideas of what may be wrong?

I have already contacted epiphone ( no schematic or info is available on the bass from them), none of the electrolytic caps are leaking or bloated and I have no way to test the ic's on the board ( I should also note that the knobs are actually hardwired to the electronic circuit board on this bass and I have heard the pots on it weren't very good but changing them for good ones isn't an option due to the way they are installed).

ok so I am personally thinking it is 1 of 2 issues at play here and I would like some thoughts ( battery is brand new energizer so I know that isn't the problem), first off old electrolytic caps that may be drying out ( bass came off the line in the Samsung plant in korea in may 1992 and is number 0803 according to the serial number S2050803).

OR

bad IC's which are 060D JRC 1041G

now I know caps are cheap so I am thinking of just going ahead and replacing all of those just because they are cheap and it isn't hard to do but just finding the exact IC's, a data sheet on them or a cross referenced replacement to the ones that are in it are proving problematic.

so I guess I am asking is do you all think replacing all the caps will fix my volume issues or do you have any thoughts as to what the problem might be? all the pots so seem to work because the volume will drop if I rotate any of them


here are pics of the bass and the circuit board:

the bass:
epiebm5ch1-1.gif


the circuit board:
EBM5board1.gif

in this pic if the horizontal switch between the 2 pots is flipped the bass doesn't work at all so any info as to what the 3 swiches on the circuit board actually do would also be of great help LOL.
EBM5board2.gif
 
#2
Cool bass, I've never seen one! My guess for the pots would be v/blend/treble/bass. Switches might be active/passive and ranges for the pots. Use some pot cleaner in the pots, clean and tighten the pin connections, and switch the 2 position switch so that you have sound. Plug into an amp and tap the pickups with a screwdriver Play with the pots and see if you can figure out volume and blend. Happy hunting!
 
#3
Oh, and my bet is that the caps are functional. I'd check all the connections to ground with a meter, then follow and check all the power and signal paths first, replace the ICs if available, then worry about caps.
 
#5
no the terminals cant be reversed but they could have shorted where the battery lead was attached to leads at the factory due to the solder locations being close together and not shrinkwrapped ( they merely taped them to the body with a piece of what looked like masking tape LOL). their is only one diode on the circuit board and it doesn't appear to be burned out ( hope it isn't anyway cause I cant read the numbers on it and epi claims they have no schematics or anything anymore for this bass.

pots aren't scratchy at all, only thing is they al have to be at 10 in order to hear it very well and then it is still not very loud. I know I had an vintage peavey vtm120H tube amp ( which I am in the process of getting back)that had a real bad buzz but also had low volume and the issue it had was with old dried out electrolytic caps which is why I was wondering if that might be the cause of the volume problem although there is no buzz or hum.

only other thing I can think of myself are those IC's but like I said I cant seem to find any 062d JRC IC's with the 1041G on them and no idea what I could use as a replacement. only thing I can think of to do would be get some old vcr's, pc monitors, etc. and tri to see if I can slavage a couple chips out of those.

another issue on the caps though is that 8 of them are 50v 4.7 uF non-polarized which I have found some on fleabay but they are expensive when compared to polarized ones ( which are more abundant) and that causes another problem because I cant install polarized caps without a schematic to show me the correct direction to install them.

now with that said I think the issues with the electrical in these bases wasn't the electronics themselves but with certain manufacturing issues ( like the way they spliced the battery terminal leads to wires without insulating them. with that said im going to look around to see if I cant find a couple of those IC's in an old monitor and replace those ( at least then it will either be fixed or I move on to the next item), have to try and salvage electronic components because I am broke right now and will be until I sell my behringer strat and my main street guitars tele.

thanks for your assist and if oyu think of anything else or if anyone has anything else to contribute, I'm all ears LOL
 
#6
well an update I just ordered 2x 062d IC's and basically every electrolytic cap on the board and will start there, after that if still no joy if you will I will replace all the resistors as well. I very seriously doubt the diode is a problem but I am trying to read the number just in case LOL. why not, I mean if I replace every electrical component on the board then the board cant be the issue then LOL and it is actually really cheap for the parts I ordered today 2x IC's and like 12 caps was only 4.35 USD from mouser, problem is the shipping was a whopping 6.99 for priority mail ( could have used standard 3 to 10 day for 4.30 or so but I want to make sure I get my parts and have never had an issue with the post office.

with that said the only pots mouser had that even came close to looking like they would work actually wont because of how they mount which is different from how the stockers mount in regard to the solder points direction :( . well im sitting with my fingers crossed LOL
 
#8
lordraptor1 said:
well an update I just ordered 2x 062d IC's and basically every electrolytic cap on the board and will start there, after that if still no joy if you will I will replace all the resistors as well. I very seriously doubt the diode is a problem but I am trying to read the number just in case LOL. why not, I mean if I replace every electrical component on the board then the board cant be the issue then LOL and it is actually really cheap for the parts I ordered today 2x IC's and like 12 caps was only 4.35 USD from mouser, problem is the shipping was a whopping 6.99 for priority mail ( could have used standard 3 to 10 day for 4.30 or so but I want to make sure I get my parts and have never had an issue with the post office.

with that said the only pots mouser had that even came close to looking like they would work actually wont because of how they mount which is different from how the stockers mount in regard to the solder points direction :( . well im sitting with my fingers crossed LOL
Click to expand...
Hi Lordraptor1 I just picked up an EBM 5 looked a little rough but cleaned up just fine and sounds great, what about rewiring the electronics and converting the the PUPS to passive.

Lee
 
#11
sorry guys but i rebuilt the circuit board and sold the EBM-5 a LOOONG time ago. i had no idea the thread was still up LOL. only basses i have now are 4 string, and are an ibanez sr400QM cherry sunburst, and a trabean phoenix bass blood red.
 

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