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Restoring a Korg Trident
MUFF WIGGLER Forum Index -> Music Tech DIY Goto page 1, 2  Next [all]
Author Restoring a Korg Trident

ttown23

So I am in the midst of trying to get this old girl running. I successfully completed repairs from the notorious leaky battery, repairing all PCB traces that were damaged, so that is good to go. But...

Sound is strange and intermittent on all sections. I checked the rails and all are good except the +5V rail... it is reading +8.5V and the pot does nothing to attenuate the voltage down. I am thinking that I need to rebuild the PSU... any suggestions?


ttown23

Also, if someone has a list of a total count of the 4000 series chips in the beastie, I'd really appreciate it!


Don T

Which version of the Trident?


ttown23

It's the Mk II, the later one.


Don T

ttown23 wrote:
It's the Mk II, the later one.


The copy of the service manual I have of that one doesn't have a parts list, so you're on your own counting the multitude of CMOS chips!

As for the power supply, aside from recapping if you haven't already, I'd check/replace pass transistor Q10, and check/replace zener D5.


ttown23

Don T wrote:
ttown23 wrote:
It's the Mk II, the later one.


The copy of the service manual I have of that one doesn't have a parts list, so you're on your own counting the multitude of CMOS chips!

As for the power supply, aside from recapping if you haven't already, I'd check/replace pass transistor Q10, and check/replace zener D5.


Good calls. I am trying to locate a repacement for zener D5, which seems to be obsolete... any ideas? Q10 is just a simple LM336Z, so that's easy enough...


Don T

ttown23 wrote:
Don T wrote:
ttown23 wrote:
It's the Mk II, the later one.


The copy of the service manual I have of that one doesn't have a parts list, so you're on your own counting the multitude of CMOS chips!

As for the power supply, aside from recapping if you haven't already, I'd check/replace pass transistor Q10, and check/replace zener D5.


Good calls. I am trying to locate a repacement for zener D5, which seems to be obsolete... any ideas? Q10 is just a simple LM336Z, so that's easy enough...


For D5, I cannot believe I found a data sheet!:

ISZ47

It is of course, in Japanese, but it appears to be a 1/4W, 6.4V Zener diode. The closest thing I found to it is NZX6V2E,133, a 1/2W, 6.45V Zener diode, which should be more than adequate. According to the ISZ47 data, it has a pretty wide tolerance, from 6.1V to 6.7V, and the NZX6V2E,133 is 2% tolerance, so you should be good there. The better news is that it'll only cost you 20 cents to find out, instead of... ...wait for it...
Link:

NZX6V2E,133


Now, as for the pass transistor, it should be a 2SD533-Y, an NPN transistor in a TO-220 package, mounted on the heatsink. If someone has put an LM336Z in its place, you most certainly have found your problem!

If replacing those doesn't help, it may be an issue with Q1, a 2SC945. Not likely though.

Photo of the above in the schematic:




ttown23

Those are all great suggestions, thanks for that...

I think you mean '2SD553-Y' and not '2SD533-Y' though, right?


Don T

ttown23 wrote:
Those are all great suggestions, thanks for that...

I think you mean '2SD553-Y' and not '2SD533-Y' though, right?


Yep, typo, sorry!


martimous

notorious leaky battery?
Yikes. I still have a rack mount Trident I bought new many moons ago. Is this something I need to be checking on? It still works (as far as I can tell)...


ttown23

Don T wrote:
ttown23 wrote:
Those are all great suggestions, thanks for that...

I think you mean '2SD553-Y' and not '2SD533-Y' though, right?


Yep, typo, sorry!


Cool, got it wink

Yeah it's not stocked by mouser but I found one on the 'bay...

I also figured that I should get ahold of the diodes/rectifiers that this baby uses... they are mostly 1S1555 and <10 of them are 1S1885. I found a suitable replacement for 1S1555, which is BA282-TR

However, I am having trouble with 1S1885. The closest I can come is 1N4002E-E3/73 Whatcha think?


Don T

martimous wrote:
notorious leaky battery?
Yikes. I still have a rack mount Trident I bought new many moons ago. Is this something I need to be checking on? It still works (as far as I can tell)...


Totally different Trident! The one we are talking about looks like this:




Don T

ttown23 wrote:

However, I am having trouble with 1S1885. The closest I can come is 1N4002E-E3/73 Whatcha think?


no idea on that one, sorry! cool


thispoison

I'll need to open my MkII up soon I think.

Everything is working fine with the exception of the memories, but I didn't realise there was a similar issue to the Polysix.

I was hoping dead battery, now I'm a little worried as I failed miserably in fixing the Polysix board. sad banana


ttown23

Well, here's something strange... C11 is missing from board KLM-385!! In the schematics, it lists this as a 1/30 electrolytic...!


ttown23

A little update...

So I took a closer look at the PSU boards, and went ahead and replaced C11. I also noted that one of the other caps, which it should have been a 10/35, was a 1/35 with a diode strapped across it. I re-capped the whole PSU board, and without any load (i.e., without all of the leads connected), I was getting +%V just fine. BUT, when I loaded the board it jumped back up to +8.4V. So I am back to thinking it's a bad voltage regulator on the +5V side. Thoughts?


Peake

I believe I've got some 945 transistors if you end up needing any. Best luck on the repair!


Don T

ttown23 wrote:
A little update...

So I took a closer look at the PSU boards, and went ahead and replaced C11. I also noted that one of the other caps, which it should have been a 10/35, was a 1/35 with a diode strapped across it. I re-capped the whole PSU board, and without any load (i.e., without all of the leads connected), I was getting +%V just fine. BUT, when I loaded the board it jumped back up to +8.4V. So I am back to thinking it's a bad voltage regulator on the +5V side. Thoughts?


Yeah, the afore-mentioned semiconductors, D5, Q10, Q1, with the addition of IC1, those make up the active parts of the +5V supply.

Before ripping out D5 though, probe with a Voltmeter on the banded end and see if it reads reasonably close to 6.4V. If it does, leave it alone. If it's not between 6.1 and 6.7V, it needs to be replaced.

I don't know where SW1 is located physically, but when on, check with your Voltmeter R9 (56K) at least one end should show +4.7V. If not, check C8 (0.1uf), VR1 (220 Ohms), R3, and R10 to make sure they are good.

Happy Hunting!


martimous

@DonT
Oh, ok. Thanks. I had never even heard of the Korg Trident II. I thought ya'll was talking about the digital Trident of a more recent vintage....
I was thinking Christ I have to go tear this down and check it...


ttown23

martimous wrote:
@DonT
Oh, ok. Thanks. I had never even heard of the Korg Trident II. I thought ya'll was talking about the digital Trident of a more recent vintage....
I was thinking Christ I have to go tear this down and check it...


Perhaps this is what you are talking about?

http://en.wikipedia.org/wiki/Korg_Triton#/media/File:Triton_rack_adjus ted.jpg


ttown23

Another update...

So the problem isn't in the PSU at all! I localized the problem to the KLM-379 signal generator board. With this board unplugged, the +5V rail reads +5V and all is well... but once I plug this board into the PSU, the +5V rail jumps up to +8.7V.

So.... I checked over KLM-379 VERY carefully, and replaced the IC 5 and 7 with TL072 OP-AMPS... no difference. Then I tested the 379-2 line (+5V rail), and it was also reading +8.7V, as well as all of the feeders into other ICs. So, I'm further along but still have no idea which component(s) on KLM-379 are bad.

Any ideas?


megaohm

ttown23 wrote:
Another update...

So the problem isn't in the PSU at all! I localized the problem to the KLM-379 signal generator board. With this board unplugged, the +5V rail reads +5V and all is well... but once I plug this board into the PSU, the +5V rail jumps up to +8.7V.

So.... I checked over KLM-379 VERY carefully, and replaced the IC 5 and 7 with TL072 OP-AMPS... no difference. Then I tested the 379-2 line (+5V rail), and it was also reading +8.7V, as well as all of the feeders into other ICs. So, I'm further along but still have no idea which component(s) on KLM-379 are bad.

Any ideas?


I would look for faults/shorts between power lines on that board.
Make sure C10 - C15 are functioning.
I was thinking it is strange you are getting +8.7V.
Could there be a short between rails somewhere?
Do the +/-15V lines and the -5V measure correctly?


ttown23

megaohm wrote:
ttown23 wrote:
Another update...

So the problem isn't in the PSU at all! I localized the problem to the KLM-379 signal generator board. With this board unplugged, the +5V rail reads +5V and all is well... but once I plug this board into the PSU, the +5V rail jumps up to +8.7V.

So.... I checked over KLM-379 VERY carefully, and replaced the IC 5 and 7 with TL072 OP-AMPS... no difference. Then I tested the 379-2 line (+5V rail), and it was also reading +8.7V, as well as all of the feeders into other ICs. So, I'm further along but still have no idea which component(s) on KLM-379 are bad.

Any ideas?


I would look for faults/shorts between power lines on that board.
Make sure C10 - C15 are functioning.
I was thinking it is strange you are getting +8.7V.
Could there be a short between rails somewhere?
Do the +/-15V lines and the -5V measure correctly?


It's funny, but all the other power rails measure correctly (-5V, +15V, -15V).

I'll check C10- C15 and see what's up there... but so far everything seems to be confined to the +5V rail.


Don T

ttown23 wrote:
Another update...

So the problem isn't in the PSU at all! I localized the problem to the KLM-379 signal generator board. With this board unplugged, the +5V rail reads +5V and all is well... but once I plug this board into the PSU, the +5V rail jumps up to +8.7V.

So.... I checked over KLM-379 VERY carefully, and replaced the IC 5 and 7 with TL072 OP-AMPS... no difference. Then I tested the 379-2 line (+5V rail), and it was also reading +8.7V, as well as all of the feeders into other ICs. So, I'm further along but still have no idea which component(s) on KLM-379 are bad.

Any ideas?


Ok, something on KLM-379 is dumping Voltage/current from the +15V rail to the +5V rail. It's not a dead short, or it would read +15V on the +5V rails on that board also.

Bloody hell! I just looked at the schematics, it WOULD be the VCO board, wouldn't it? I mean, there's only 16 VCOs and their related circuitry. And, if it's built anything like a Polysix's voice board, isolating each circuit is basically impossible. And in this case, it seems doubtful a CMOS chip is the problem, as they are powered by the +5V line. At this point, it could be any single component that is powered off the +15V rail, or connected to it. C11 would be a likely suspect, but in truth it could be anything. Too bad you aren't nearby, I'd loan you my cap checker. It can test for ESR and DCR with the caps in circuit.

See if someone nearby has something similar to this you can borrow:

B&K Model 881 Cap Tester

You can check ALL the caps in about 5 minutes, and it will tell you which ones are good, dead, or dying. If all the caps turn out to be good, it'll be time to check opamps (all those 4558's) and JFETs next.

Also, take the board out, and hold it up to strong light, and look for any burnt or toasted spots. Those will leak Voltage, and ruin your day. Also, look around the electrolytic caps to see if they are glued down with stuff that looks like old contact cement, if it starts turning black-ish in color, it can also become conductive.


BugBrand

Could it be the decoding 4051 (IC8) - strung between +5 and -10V.
Those cmos muxs can go bad, no?
Well, it'd at least be an easy swap..

(guess!)

Further - the -10v is only used around that input mux -- generated by IC4 along with Q3 etc - could be worth a probe around to check if that is working correctly.

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