Bassbase 600 - Can anyone offer advice on how to open the amp up?

Old thread, but I’m hoping someone can help. My lights went out on my Bassbase 600. Can anyone tell me how to access them? Do you have to attack it by taking the bottom of the amp off? There seems to be an aluminum cover over the front panel when you look at the inside of it from the top.

I've moved this post into its own thread to get a bit more exposure for it Frootbooty. I'll include the Bassbase amps in the Basskick forum title too so they aren't left out in the cold.

I haven't come up with any useful info on how to break down the amp to get to the bulbs. I'll keep on digging and pass on anything I find.

Anyone else have any inkling about this?

This is pretty obvious but the bulbs are all in series and fed direct from the 62V AC secondary of the mains transformer.  T10 bulbs are 12V and 5x12V = 60V so there is a 10R resistor in there with them to balance up.

The fact that they are in series means that, if one goes they all go out!  The most likely thing to be wrong is a blown bulb.  It is possible there may be more than one.  It is also possible there may be a bad joint of some sort, most likely a mechanical joint at a bulb rather than a dry solder joint.  (A bad solder joint on a PCB is extremely rare despite internet scuttlebutt telling you every other joint is likely to be bad.)  It may also be possible that the resistor has burned out too but again, that's extremely unlikely.

The lights should be fed from the power supply PCB.  The plugs 1 and 7 should be the 62V feed and the return to ground through the resistor.  These plugs are on the edge of the PCB at opposite ends.  Plug 1 is the outermost of a long line of 12 plugs and plug 7 is on the other end of the board in the same position.  I would hope these are numbered anyway but if you can't locate them get back to me.

From what I can see in pics of the amp the top panel comes off with 10 screws, I think you have got that far.  Then, from what you say, there will most likely be the PCBs for the preamp sections mounted flat onto the front panel with a flat screening cover over them.  My guess is that the front panel comes off first rather than accessing this area from behind.  There are screws in the front panel as you look at it from in front.  Have you tried taking those off?  Have a look and see if they hold anything on behind them too before you remove them all.

Does that fit with what you are seeing with the top panel removed?

I have a black face model without screws on the front panel. There are some screws along the side toward the front that I’m guessing release the front, but I’m a bit scared. I remember I had a silver one that I unscrewed the screws on the face of it and all the little labels seemed like they wanted to drop out and some of them got a bit wonky and crooked.

I hadn't seen the difference between some metallic models and your blackface one FB.  It's odd that they have used a different method of mounting the panels in each type.  The screws on the side seem like the most likely candidate to release the front section.  Can you see down into the area behind the front panel to maybe take a pic of the back end of those screws inside?  If they are more than a few mm down inside the space the nuts they screw into must surely be captive.  You wouldn't design a production model which had an extremely fiddly build procedure.  We do it with prototypes and "homers" but the build procedure is simplified and quickened for the final release versions.  I agree that if you are worried about it the last thing you should do is to merrily unscrew and have everything spring apart on you so you can't get it back together again without the custom jigs to hold things.  We try as much as possible not to be "pedal bodgers" or "Marshall modders" here.

Any chance of a look in at the back of the screws or are they too deep inside or simply covered completely?

Update: I replaced the bulbs. At some point a previous owner switched them to leds. Anyway, after I replaced them, they still aren’t coming on. The first two bulbs from right to left illuminated a little as I plugged them in, but didn’t stay on once fully plugged in. The last three bulbs would not light at all. I don’t see any wires off, and all fuses appear intact. I contacted the service dept to find a repair person in Vegas now because I’m at a loss with my limited knowledge.

This may still be easy for you to fix Frootbooty.

First of all, how did you get to them in the end?  Where were they situated?  Was my description of the lighting system correct when I said it should be from the two connectors on the corners of the PSU PCB?  That could be information which will be really helpful to other owners with the same problem.  I have looked again for info on this and couldn't find a single pic of the inside of an opened BassBase so I'm still in the dark as to the real details.

You say someone had already exchanged them for LEDs.  Can you post a close up picture of one of those LEDs?  I would assume you meant that they had simply inserted the automotive LED replacement for your original T10 bulbs which should be a simple plugin replacement.  Those automotive versions are, in reality, LED "indicators" and not just straight LEDs.  I've posted a pic to show you what I mean.  Yours may not look exactly like that, there are many types out there, but you should be able to spot if it has extra components in it to the LEDs themselves.  They sometimes have more than one LED per bulb and each has a current limiting resistor on board to make sure they will all work correctly from a 12V supply.

Now the real point.  They may not have used those and, if they have somehow just taken 5 plain LEDs, they will have had to work out the correct value of resistor to set the current to the much lower level than a bulb.  (That is actually easy to work out!)  They would then have had to add additional resistance to the original 10ohm (10R) in somewhere as part of the mod.  If that is the case then your bulbs will not work with the resistor still in place!  LEDs take <20mA and T10 bulbs take >400mA.  The plain bulbs need to see a straight 60V supply fed from the 10R PCB resistor otherwise the current will be far too low for them to work as they should.  From your description of the first one or two actually working dimly, it really sounds like you have too much resistance in the circuit for bulbs.  That could be a leftover of the LEDs having been installed.

It is also possible that they have used a length of "LED strip" which is the flexible line of indicators which are fed from one end from a 12V source. These are very commonly used by modders in this sort of application. If that is the case they will certainly have had to add resistance to drop the 60V supply down to the 12V the strip must see and that would be your problem.

Are there any other components you can see in there which look like they have been added or changed?

Here is what I removed from the plugins. Your description of the lighting mechanism is pretty accurate. I don’t see any other modifications inside the amp. I wondered about the resistor myself, but I have used this amp for maybe six gigs recently that lasted about four hours each. I didn’t know if the lights would have worked that long if that was the problem.

Can you direct me to anywhere online I can get the exact or very close to the original bulbs that came in the amp originally? I’ll try that and see what happens next.

That is definitely a LED type, (looks like 5x LEDs on there), but I can't see whether it has resistors in (acting as a self contained "indicator") or whether it is a straight LED unit with no current control.  Nowadays I really would have thought the first option was the one.  If you could slip the blue base cover off you may be able to see if there are tiny black/grey resistors on the PCB though it's not strictly necessary.

You should be able to pick up the original incandescent bulb types from any auto-parts outlet local to you or online from Amazon/ebay etc.  Just ask for 12V 5W T10 incandescent bulbs and specify NOT LED types, (though that is what the "incandescent" should tell the sales guy).  Those are the original spec.  Just make sure they are see through with the filament inside like the picture attached.

If the resistor has been replaced or added to and that is the problem meaning you now have a mismatch in types, the lights would not have worked for you at all at your gigs, at least if they are still wired as the schematic shows.  They are all in series.  If either the resistor or just one bulb blows or is removed they all go out.  Period.  Is it possible that the wiring has been damaged somewhere prior to you getting the amp?  If one of the connecting wires from the PCB to the lighting circuit is pinched, and that can happen when taking covers off for valve changes and replacing them for example, it may look whole but may have been broken inside.  You should easily spot a potential problem "crimped" point in the wire.  Also check the two terminal connectors on the corners of the PSU board, (they look like they might be simple automotive spade types to me).  If the wire has been used to pull the terminals off it may also have been damaged at the crimp.  People do these things without thinking sometimes.

I guess my only concern is if the issue was leds without a resistor, would I have gotten that much time out of them before they went out? That makes me wonder about a wire, although the wires appear fine. Also, the lights appear to have died between gigs, as in they were working last time and never came on this time. The amp is racked and never got jarred or dropped to my knowledge.

The only real reason the LEDs would have worked then died on you is if the resistor had been badly calculated and they were running with too much current. If they were LED indicator types with their own resistor onboard that shouldn't be a problem. Is it possible you just have a poor contact in one of the sockets?

What you say about them working at switch off then not at switch on next time is pretty much what you would expect to see. Most incandescent lights go out at switch on because they have a lower resistance when cold which means a current surge until they heat up and come on. That's only a fraction of a second but it is generally how it goes. You click the switch, there is a ping and a short flash and the light stays off. LEDs are different of course and are stabilised by their current limit resistor right from the instant the switch is thrown. They don't run at high temperatures as a bulb does. If yours have been running at too high a current for a while the thermal shock from stone cold to coming to temperature could be enough to blow one. They don't run terribly hot as normal but they are semiconductor devices like transistors are and they do not stand higher temperatures for ever.

I think your best bet is now to give the T10 5W incandescent bulbs a try out as they are so cheap. Just put a full new set of 5 in there and switch on. Failing that fixing it, if you can post more close up pictures of the insides of your amp, that dropper resistor and the PSU PCB for example, we might be able to spot something. Other than that it is give it to a tech to have a look see. It should be a fairly simple fix when the problem is accurately located so it shouldn't be too expensive.

Well, got some bulbs from Autozone, and there you have it. Not blue anymore, but I kind of like the soft white look. I really appreciate all your help on this.

Hahaha! So it was a simple interaction with the LEDs in the end. Glad you got it fixed without any additional cost. Can I ask you to maybe post a couple of quick pics of the way you managed to get into the bulbs? This might be helpful for others in the future.

You are very welcome for the advice such as it was. Get the amp back into service and gigging. That's what they are there for after all.

With the top off, the bulbs sit inside this white aluminum rectangle. There is a thin aluminum strip that runs across the front of the bulbs, perhaps to disperse the light or perhaps to keep them from getting broken. It’s not possible to remove the bulbs with that strip covering the front of them. Therefore, I had to remove the bottom of the amp also. Once the bottom was removed, I unscrewed the 6 screws to free the front of the amp. I removed the tube and unplugged one multi pin connection that allowed me to then pull the front out far enough to access the screws on that aluminum strip. Once the strip is off, you are looking right at the bulbs and can just pop them out and pop the new ones in. None of the screws on the bottom appeared to hold anything in place inside the amp, which is what I originally feared. They only held the cover in place, so I didn’t have any of the guts moving around inside. In the second pic you can see where the lights feed into the back of the aluminum housing. The only reason I had to remove the bottom was to unplug that multi pin connector as it was at its end and I couldn’t pull the front out any more with it plugged in.

Thank you very much, that is really useful information to have here.  I think I might even use your info to put a new thread here in the Bassbase forum specifically for it.  This info doesn't seem to be available anywhere else on the internet.

I think you might even be able to remove the bulbs and their holders from behind with just the top off.  The ones in your pic look the same as automotive versions which are just a push/twist fit into a round hole with two further rectangular access slots in the metal panel.  The overall shape is a bit like Green Lantern's symbol.  The bulb holder has two little lugs which fit into the rectangular slots then twist round on the opposite side of the panel locking the holder in place.  Sometimes they can be a bit stiff but that's the usual way to remove and refit them.  I've attached a picture of it.  If you need to get at the bulbs again try twisting them about 90 degrees firmly from behind.  You may even have to gently grip them with pliers as you twist but they should turn then come out in your hand.  You can then fit the new bulb and twist them back into place.

Anyway that will be a useful addition to the Bassbase section and maybe for some other models too.  And the pictures are brilliant.  You're an internet trailblazer!