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Thread: JCM 2000 bias pins maxing at 15mV

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    JCM 2000 bias pins maxing at 15mV

    I've replaced the mains inlet pcb and power transformer. Previous owner had a 25a main fuse in it and fried them both. They were relatively simple to repair and now the amp at least turns on, where before it was blowing fuses immediately on power up.

    First thing I did was attempt to bias from the pins located on the back. Service bulletin calls for 80 mV and I'm maxing the bias pots out at 15 mV with amp connected to a load and heat up time of approximately 20-25 minutes.

    Also, I plugged a guitar in and my ultra gain is humming at only 20% gain. The amp doesn't sound horrible through classic gain but its definitely missing something. Where as my low end is almost non exsistant in ultra gain.

    So far I've been told that its likely that my board is conductive between the pins of my output tubes. But by my understanding this common problem results in high bias readings and mine aren't even close. In fact, I'm weary of playing my amp at all for fear of my amp playing too cold. But thats just a hunch, no real knowledge to back that up.

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    Supporting Member Randall's Avatar
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    What you are doing at the back connector is reading voltages across a 1 ohm resistor on the cathodes of each pair of power tubes. Since it's 1 ohm the math works out to mV = mA, so in your case we can say your pair of tubes is drawing 15 mA. It's very low, but it won't hurt anything. A current draw of this low usually means the grid is seeing too much negative bias voltage. The higher the negative bias voltage applied, the colder the tube will run (draw less current). These boards usually conduct some of the positive plate voltage to the grid pin, causing it to go less negative and therefore conduct more. In some cases, a lot more until the tube dies or the board burns up.

    I'd measure what the voltages are on pin 5 of the EL34s, and I'd also have a look at those 1 ohm resistors. Also, you didn't say if these are known good tubes or not, if they were in the amp when it blew up, they may just be pooched.

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    It's weird, because it WAS working fine.....

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    Old Timer Leo_Gnardo's Avatar
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    I'm thinking, if the amp owner wrecked his PT by installing 25 amp line fuses, there may be other problems lingering in this prize. That PT likely didn't decide to melt down on its own, there's got to be a reason for it. Now there's a new one you are wise to track down & fix the problems. How are the screen grid resistors? If they roasted and increased in value, that would explain an inability of the output tube to move much current. Same for the 270R cement block resistor that knocks down hi voltage to appy to those screen grids. Of course check the bias voltage as Randall suggests, it should be in the -40V region.

    If this JCM2000 was made 2006 or before it's suspect to have the dreaded conductive circuit board problem. Far and away the best solution is replace the board. Big bucks, lots of shop time, long wait for an overseas shipment. There's also the solution worked out by our German friends at Hullerum, read here:

    The Marshall TSL122 TSL100 thermal bias drift repair page

    More JCM 2000 problem areas by Rich Koerner in sunny downtown Union NJ, I could swear there was text to go along with this but follow the arrows & you'll see things that may need attention:

    Rich Koerner's Time Electronics Picture Gallery of Repairs & amp Nightmares, A Marshall 2000 TSL-100 Repair

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    Every resistor that I've been led to has tested the correct resistance. I agree it wouldn't be a bad idea to try and find a bad one, and that is my next venture when time allows.

    On another note though, my tubes passed the continuity test. I'm sure there is more too them being good than just that but I have an option of buying new tubes and seeing if one is just struggling or buying the new PCB and getting it over with to avoid pouring more money into it, to no avail. Obviously prefer it just being the tubes but unfortunately things don't always happen as you prefer. ��

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    Don't forget the joker g1's Avatar
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    Pull one of the power tubes and measure the DC voltages in the socket pins. Report your readings.

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    "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

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    Senior Member TimmyP1955's Avatar
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    I just did the Pin 5 mod to one and the bias seems to finally be stable.

    I had previously done another mod - I replaced R77 (common feed to the two pots) with two resistors to feed the pots independently; Replaced R68 (common load on the two pots) with two independent load resistors. (I placed these on the little pot board.) I did this in the hope that the interaction between the pots would be reduced (I am not convinced it was - or wasn't).

    Make sure that the grid stoppers are 5k6 - some of these amps have 220k!
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    Ok, so I've tested all resistors on the main pcb, and to no surprise there were some not matching up. My schematic reading isn't top notch but I've noticed a pattern of them all being in groups. I can put together that something in that grid isn't working properly. I just don't know how to pin point what exactly. I'm going to go ahead and buy some resistors in hopes that those are what's causing the problem.

    Here's the groups of resistors that were off in testing.

    R39 100k tested at 31.2k
    R40 47k tested at 19.7k
    R41 47k tested at 19.7k
    R44 22k tested at 18.6k

    Make sure that the grid stoppers are 5k6 - some of these amps have 220k!
    I believe my amp is an amp that has the 220k in these places. Which if I'm not mistaken are R7, R66, R70, and R10.

    And lastly,

    R64, R72, R73, R75 all supposed to be 220k and they tested at 170k. And they took like 10 minutes to stabilize, is that normal?

    I'm kind of at the end of my knowledge at this point. I have been reading everything I can, but I'm limited in experience so any advice is greatly appreciated!

    P.S. To those that instructed me test the pins on my outlet tubes. I'm not ignoring your instruction, simply just don't have the board in at the moment.

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    Last edited by Djizix; 03-01-2017 at 06:50 AM.

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    Stray Cap DrGonz78's Avatar
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    Quote Originally Posted by Djizix View Post
    Here's the groups of resistors that were off in testing.

    R39 100k tested at 31.2k
    R40 47k tested at 19.7k
    R41 47k tested at 19.7k
    R44 22k tested at 18.6k

    I believe my amp is an amp that has the 220k in these places. Which if I'm not mistaken are R7, R66, R70, and R10.

    And lastly,

    R64, R72, R73, R75 all supposed to be 220k and they tested at 170k. And they took like 10 minutes to stabilize, is that normal?
    This to me sounds like you might be measuring the resistance while in circuit. For example, you say took 10 minutes to stabilize and I am having trouble understanding what you mean. This will confuse the meter when other components are in parallel and 47k might read 19.7k. Many time to read them correctly you need to lift a leg off the board. Also, is this a DSL or TSL? Please post the schematic to which you are referencing your board version. I am working on a DSL in my shop at the moment and this is the schematic I am using. Seems to match up to what you have mentioned so far. If so some of the resistors that you are testing are not really in the scope of the issues you are trying troubleshoot. Then again maybe I am missing something since I am unsure of the schematic you are referencing. Best Regards.
    Attached Files Attached Files

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    Last edited by DrGonz78; 03-01-2017 at 08:32 AM. Reason: To fix link to schematic
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    It is a DSL. And from what the previous owner tells me, its from 2001.

    This link http://drtube.com/schematics/marshal...01)%20iss7.pdf is the schematic I'm using.

    And if I'm understanding you correctly, in order to read resistance on, for instance, R40 on this schematic, I need to detach one leg of the resistor from the board? Or do you mean one leg of the meter?

    Also, you mentioned that these misreadings aren't in the scope of what I'm trouble shooting. I just assumed that testing all the resistors would be a good way to analyze my problem, judging by the comments I've received thus far. So if they're unrelated would it be a mistake to leave these resistors as is, reinstall my pcb back in the chassis and try some of the tests on my output tube pins, as stated before?

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    Stray Cap DrGonz78's Avatar
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    Yes detach (lift) a leg of the resistor off the board to take it out of circuit to get an accurate reading of the individual resistor. Some resistors to be concerned with to start are the grid resistors R7, R66, R70, and R10, like you mentioned. That is is a good starting point and making sure they are updated to 5k6 like in the schematics attached. Also, do some inspections on the bias board itself and make sure those variable resistors (bias pots) are functioning well. At that point we need to go back to testing voltages as G1 pointed out. Testing B+ voltage and negative bias supply voltage to really see what is going on.

    Edit: Also don't forget to check out those screen grid resistors as Leo had pointed out which are R60, R65, R74 & R76. First test them without removing them from the board and see if they measure 1k. If they measure higher resistance than expected then you will have to remove them to test further. R64, R72, R73, R75 were the other one's Leo had you check which was good since they all measure 170k in circuit. I don't think they drifted high. I just saw that you might go hunting other resistors that were not related to problem at hand.

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    Last edited by DrGonz78; 03-01-2017 at 11:08 AM.
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    Stray Cap DrGonz78's Avatar
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    Quote Originally Posted by DrGonz78 View Post
    R64, R72, R73, R75 were the other one's Leo had you check which was good since they all measure 170k in circuit. I don't think they drifted high. I just saw that you might go hunting other resistors that were not related to problem at hand.
    Sorry it is late. Note that R64, R72, R73, R75 are just bleed resistors and that I meant to say check for drift on R71 that 270R resistor Leo mentioned.

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    Lifetime Member Enzo's Avatar
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    Don't obsess over resistor values. Resistors almost never go low in value, and especially not like from 47k to 19k. They do go high when failing at times. Low resistances are invariably just parallel current paths in the circuit. If you have a legit reason to suspect a particular resistor, you can unsolder one end, but going through the amp unsoldering part after part is more likely to cause more problems than solvve anything.

    Screen grid resistors have a tube screen on one end, they are already about as out of circuit as you can get. No need to unsolder them.


    When you increase the tube current by lowering the bias, it drags the B+ voltage down. This of course affects the other side tubes. THAt is why the two controls interact. You set one, then that changes the B+ voltage for the other one. So you adjust that one and now the first one changes. You go back and forth a few time until it all centers.


    Please stop calling these things JCM2000s, there are numerous models in the JCM2000 line. JCM2000 doesn't specify a model. It is like saying "I have a Chevrolet." Well is it a Malibu? a Corvette? An Impala?

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    Ok. I will get the board put back in and start testing as instructed. I'll let you all know what I find. Appreciate it!

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    So I tested the 22k variable resistors on the bias board to the best of my ability. I'm having trouble identifying which is positive and which is negative, but I'm fairly sure I have the neutral nailed down. Either way, I alternated the black lead accordingly and my readings were on one side, fluctuating around 11-22k and the other side was 14 ohms turned counter clockwise, and 25 ohms clockwise. Doesn't seem right, but I don't really know.

    UPDATE: Got the amp back together, plugged it in, hooked up to a load, standby for 10 min, and powered up. My bias is now reading 8 mV on the left side pins, and 130 mV on the right side pins. Which caused my left two tubes to get a little too hot for my comfort. I immediately shut it off after and haven't resumed testing.

    So, if I'm gathering the clues correctly...I, in fact, do have a thermal drift, or at least the same symptom now. Whether or not I caused it while taking the board out, or this is just my first time witnessing it occurring, is beyond me...

    So basically, my symptoms changed from being not enough, to way too much on just one side... With or without the proper knowledge of the field, I think this is a pretty easy decision...just not as cost effective as my wallet hoped for.

    If you guys have any other suggestions, I'm open minded to new solutions. But I have a feeling my only option is to try and do the drilling pin 5 out routine, and I'm not up to the task. Thanks guys.

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    Last edited by Djizix; 03-02-2017 at 07:45 AM.

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    Supporting Member Randall's Avatar
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    It's weird, because it WAS working fine.....

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    Old Timer Leo_Gnardo's Avatar
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    Quote Originally Posted by Djizix View Post
    If you guys have any other suggestions, I'm open minded to new solutions. But I have a feeling my only option is to try and do the drilling pin 5 out routine, and I'm not up to the task. Thanks guys.
    So you don't have another annoying too high / too low test run again, check the bias voltage on pin 5, all output tubes before commencing. I'd recommend, dial the adjustment pots so that you read say -43.0V if you can get there, or as close as you can. Same bias V for each pair of tubes. Warm up your prize, read the bias on the test points, it will start out low then increase as you adjust the bias pots closer to -40V.

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    Quote Originally Posted by Leo_Gnardo View Post
    So you don't have another annoying too high / too low test run again, check the bias voltage on pin 5, all output tubes before commencing. I'd recommend, dial the adjustment pots so that you read say -43.0V if you can get there, or as close as you can. Same bias V for each pair of tubes. Warm up your prize, read the bias on the test points, it will start out low then increase as you adjust the bias pots closer to -40V.
    I've tried swapping tubes around and have gotten the same result every time I fire it up. And I'm not 100% how to test the bias voltage on pin 5 either. I'm confident that a new PCB would fix the problem and I know I have the ability to install it. But for the sake of knowledge, I'd love to know how to test the bias voltage in case I run into similar problems in the future.

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    Old Timer Leo_Gnardo's Avatar
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    Quote Originally Posted by Djizix View Post
    I've tried swapping tubes around and have gotten the same result every time I fire it up. And I'm not 100% how to test the bias voltage on pin 5 either.
    Clip your meter common probe on chassis ground. Put your meter measuring probe on pin 5. Turn on the amp. Read the meter. Now you are reading the voltage on pin 5.

    I'm asking for readings on ALL the output tube sockets in case say you have the bias voltage at -45V for one pair and -35V for the other pair, that sort of thing would explain why you're getting widely different bias readings from the test points. It would make sense to start with the bias voltage matched and on the high side, that is further away from zero, then adjust to the appropriate level.

    I fear that if you cannot make these kind of measurements you're over your head with or without a new board, and perhaps this task is best left to someone with more expertise. Where are you located, perhaps some kindly MEFster is within easy driving distance, you could take it there and get help.

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    Quote Originally Posted by Leo_Gnardo View Post
    I fear that if you cannot make these kind of measurements you're over your head with or without a new board, and perhaps this task is best left to someone with more expertise. Where are you located, perhaps some kindly MEFster is within easy driving distance, you could take it there and get help.
    I'm located in southern Illinois, at least 2 hours from any big towns with any known techs that I am aware of. Which is why I've tried to tackle this myself. I'm at technician full time and work with electricity regularly. I'm not flying completely blind, I'm just not as experienced with circuitry. Trouble shooting amplifiers is something I'm trying to learn simply because I'm a lifelong musician. Not to say I wouldn't take help, that's the reason for this thread.

    That being said, I suppose when I said I wasn't 100% sure how to do it, I didn't mean I didn't know how to test voltage. That's pretty cut and dry. Perhaps though, I was measuring this bias voltage wrong because my reading wasn't a negative voltage when I attempted this.

    So again, if I'm understanding this correctly, I'm to take one tube out at a time, ground to black, and red to the pin 5 insert of the extracted tube? And when and if I test it correctly, the bias pots will adjust this at an appropriate level of negative voltage?

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    Old Timer Leo_Gnardo's Avatar
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    Quote Originally Posted by Djizix View Post
    So again, if I'm understanding this correctly, I'm to take one tube out at a time, ground to black, and red to the pin 5 insert of the extracted tube? And when and if I test it correctly, the bias pots will adjust this at an appropriate level of negative voltage?
    OK then looks like we have enough confidence to press on, good . Also, you never know where us MEFsters are, scattered around the globe, places populated and others not so much (hear me you guys on Prince Edward Island?)

    You could do it that way, or if chassis out of box, you could approach pins 5 from the back of the circuit board, with tubes in sockets, no need for removal. Of course being careful as I'm sure you know how, one hand in your pocket so you can't get a shock. Another of this amp's unexpected quirks, the bias trim pots adjust the pair of tubes - and test point - opposite the trim pot location. Another Marshall circuit trick to drive us crazy.

    Perhaps though, I was measuring this bias voltage wrong because my reading wasn't a negative voltage when I attempted this.
    Possible we're not square on the bias voltage = the voltage you measure at the control grids of the output tubes, pins 5, should be somewhere between say -37 and -42V once we're done and everything's working right. Not to be confused with the bias test point voltage, what you measure on those handy pins sticking thru the pan covering the bottom of the circuit board, there you'll see millivolts on the two outer pins, with the center pin common. Each millivolt corresponds to a milliamp of bias current. What you're measuring here is the voltage across a pair of 1 ohm current sensing resistors placed between ground and output tube cathodes, in pairs. When things are running right, I like to see about 70 mV on each test point though Marshall specs 90. My opinion, others may differ if they wish, 35 milliamps per EL34 is enough.

    I hope this helps!

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    Stray Cap DrGonz78's Avatar
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    Quote Originally Posted by Djizix View Post
    So I tested the 22k variable resistors on the bias board to the best of my ability. I'm having trouble identifying which is positive and which is negative, but I'm fairly sure I have the neutral nailed down. Either way, I alternated the black lead accordingly and my readings were on one side, fluctuating around 11-22k and the other side was 14 ohms turned counter clockwise, and 25 ohms clockwise. Doesn't seem right, but I don't really know.
    Something about this part of your observations here needs more understanding. If one side is 11-22k and the other bias trim pot adjustment is between 14-25ohms then something there needs to be looked at better. I guess this part left me confused a bit as to whether I understood it correctly. Then I read that one pair of tube is pulling a butt load of current and the other is barely pulling any. Of course measure your pin 5 bias supply voltages like Leo mentioned first. Still perhaps there is something off about that that Bias Board adjustment readings.

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    Quote Originally Posted by DrGonz78 View Post
    Something about this part of your observations here needs more understanding. If one side is 11-22k and the other bias trim pot adjustment is between 14-25ohms then something there needs to be looked at better. I guess this part left me confused a bit as to whether I understood it correctly. Then I read that one pair of tube is pulling a butt load of current and the other is barely pulling any. Of course measure your pin 5 bias supply voltages like Leo mentioned first. Still perhaps there is something off about that that Bias Board adjustment readings.
    Hmm, how to explain it...both pots measured the same. What I meant was when I'm on the positive side (I think) if fluctuates from 11-22k. When I'm on the negative side it measures the 14-25 ohms (14 when the pot it set to minimum and 25 when maxed)...I dont know what those resistances should measure at because I dont fully understand this variable resistor...it has a 22k max I'm assuming from the letters on it. But what Im calling negative shouldnt test at low resistance like 14-25 ohms should it.

    Also tested pin 5. On the left pair I was able to get my bias voltage at -35v. This is the side that is biasing at 130mV. Yes I know the pins are backwards. The right side pair was at -48v. This side would only bias at 8mV. So I have no idea where tis leads me.

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    Old Timer Leo_Gnardo's Avatar
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    Quote Originally Posted by Djizix View Post
    Also tested pin 5. On the left pair I was able to get my bias voltage at -35v. This is the side that is biasing at 130mV. Yes I know the pins are backwards. The right side pair was at -48v. This side would only bias at 8mV. So I have no idea where tis leads me.
    That set of figures, makes sense. Given those bias voltages we'd expect the tubes to act that way. It looks like there's something amiss with the bias control card, maybe one or both of the pots are kaput. "Fluctuates" doesn't sound healthy, and a pot that ranges from 14 to 25 ohms only doesn't sound good either.

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    Supporting Member Jazz P Bass's Avatar
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    Here is a schematic of the 'bias' board.

    jcm2-64-02.pdf

    If you want to test the controls, unhook the connector at the main board.
    At the bias board header, measure the resistance from pin 1 to pin 2 & from pin 1 to pin 6.
    When you rotate the adjustments, the value should change from zero ohms at one end of the adjustment to 22K at the other.
    Both controls should read the same.
    Reading across pin 1 and pin 7 should be double the value of each 22K control. (they are in parallel).
    The adjustment screw has no affect on this reading.

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    I will tear her open and test as soon as time allows. In the meantime though, if I do have shot variable resistors, would anyone have any idea where to get a matching set? Id prefer to not have to mod this tiny little chip. Also, does anyone know if a new pcb would come with a new bias chip?

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    Old Timer Leo_Gnardo's Avatar
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    Quote Originally Posted by Djizix View Post
    I will tear her open and test as soon as time allows. In the meantime though, if I do have shot variable resistors, would anyone have any idea where to get a matching set?
    Mouser's my go to parts place. I narrowed the selection somewhat but you'll have to pick the trimpot that has the approprate pin locations for the Marshall board. Here's a selection from 20K to 25K.

    I'm sure Digikey, maybe Newark or Allied will also have these or others like them.

    http://www.mouser.com/Bourns/Passive...yzbppyZ1z0z54u

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    Quote Originally Posted by Jazz P Bass View Post
    Here is a schematic of the 'bias' board.

    jcm2-64-02.pdf

    If you want to test the controls, unhook the connector at the main board.
    At the bias board header, measure the resistance from pin 1 to pin 2 & from pin 1 to pin 6.
    When you rotate the adjustments, the value should change from zero ohms at one end of the adjustment to 22K at the other.
    Both controls should read the same.
    Reading across pin 1 and pin 7 should be double the value of each 22K control. (they are in parallel).
    The adjustment screw has no affect on this reading.
    They tested fine, so I suppose its time to get the new pcb on order. Has anyone had any trouble with the reissue that theyre selling now?

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    Stray Cap DrGonz78's Avatar
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    https://www.amplifiedparts.com/produ...acement-dsl100

    That is the source that I know of to replace the main board on the DSL100. Pretty expensive but it does help rebuild your confidence in the reliability of the amp again. Did you every measure bias voltage at pin 5? Also, it is wise to check all the output speaker jacks to see if any are worn out and open. The jacks are supposed to be closed circuit when no plug is inserted. I have one here that one of the 4 ohm jacks tip is open and will not mechanically close any more. That part needs to be investigated either way if you buy a new board or not since your still going to be using the output board in the amp.

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  29. #29
    Old Timer Leo_Gnardo's Avatar
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    Quote Originally Posted by DrGonz78 View Post
    https://www.amplifiedparts.com/produ...acement-dsl100

    That is the source that I know of to replace the main board on the DSL100. Pretty expensive but it does help rebuild your confidence in the reliability of the amp again.
    Ambiguous answers as of 8 Nov 2016, apparently out of stock, they're expecting to have them by the end of May. Woops check that, another answer says they expect to have them in 2 or 3 weeks, that was 1 Dec 2016. Better call to find out for sure.

    Otherwise, excellent find DrGonz! And in your neighborhood too. If they're in stock, sure beats sending away to England, in hassle, time waiting for delivery and $$$.

    Antique and CE customers take note, same part #. What a coincidence!

    Also, it is wise to check all the output speaker jacks to see if any are worn out and open. The jacks are supposed to be closed circuit when no plug is inserted. I have one here that one of the 4 ohm jacks tip is open and will not mechanically close any more. That part needs to be investigated either way if you buy a new board or not since your still going to be using the output board in the amp.
    ??? Closed circuit, as in shorted like Fenders? I know there's a feature in the output jack field that DISconnects the 4/8 ohm jacks if there's a plug inserted in the 16 ohm jack, intended to prevent users from driving speakers from both taps at once. And how many times I've found the switch built into the common electrodes of the 16 ohm jack with its contacts roasted, no longer making a good connection to the 4/8 jack pair, one more quirk to beware of in this series of amps.

    It's been said before, so I'll say it again. If this series of JCM2000 amps were cars, Marshall would have to conduct a recall program and fix their problems at no cost to the customer. Add that to your aggravation list folks. Grrrrr......

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    Last edited by Leo_Gnardo; 03-06-2017 at 04:49 AM.

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    Stray Cap DrGonz78's Avatar
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    Quote Originally Posted by Leo_Gnardo View Post
    ??? Closed circuit, as in shorted like Fenders?
    Sorry my wording was confusing there, I really meant Normally Closed (NC). Just that the normally closed latching switch part of the jack gets worn to point that it does not latch closed any more.

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    Senior Member TimmyP1955's Avatar
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    I think that the second one down is the bias pot you need. Marshall Amp Parts - Marshall Pots

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  32. #32
    Stray Cap DrGonz78's Avatar
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    Quote Originally Posted by TimmyP1955 View Post
    I think that the second one down is the bias pot you need. Marshall Amp Parts - Marshall Pots
    Not so sure if that would fit the JCM (TSL/DSL 100) series bias boards. The types that are in there are more like these ones...
    0.15w Linear Horizontal Variable Resistor - Preset - Trimmer (5 Pack) 100R to 1M | eBay

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    Last edited by DrGonz78; 03-07-2017 at 08:07 PM.
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    Senior Member TimmyP1955's Avatar
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    I believe you are correct.

    I think the best thing would be to trash the dual pot crap and make it into a 'normal' single pot bias circuit that most amps get along with just fine. I'd prefer to use a "real" pot, but where to put it?

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    Stray Cap DrGonz78's Avatar
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    Quote Originally Posted by TimmyP1955 View Post
    I believe you are correct.

    I think the best thing would be to trash the dual pot crap and make it into a 'normal' single pot bias circuit that most amps get along with just fine. I'd prefer to use a "real" pot, but where to put it?
    There is this example here that does just that.
    The Marshall TSL122 JCM2000 Repair/Mods Page

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    Quote Originally Posted by DrGonz78 View Post
    Also, it is wise to check all the output speaker jacks to see if any are worn out and open. The jacks are supposed to be closed circuit when no plug is inserted. I have one here that one of the 4 ohm jacks tip is open and will not mechanically close any more. That part needs to be investigated either way if you buy a new board or not since your still going to be using the output board in the amp.
    So, was this a general suggestion, or an implication that my syptoms are related? The new PCB is in and hooked up and I'm getting the exact same syptoms. My next two ventures are the bias pots, which tested correctly, and the output jacks. I am now in the process of testing the jacks. The two contacts are reading differently on all 3 output jacks, I'm just not sure what it means. The jacks have two contact points. They're all testing for continuity when nothing inserted. The 16 ohm jack is testing no continuity when inserted on both contacts. The middle 4/8 ohm jack is testing continuity on both contacts when inserted. The end 4/8 ohm jack is testing continuity on the first contact, and no continuity on the second contact.

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    Last edited by Djizix; 03-14-2017 at 07:19 AM.

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