Author Topic: Replacing GR 300 power supply capacitors  (Read 415 times)

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Offline chrish

Replacing GR 300 power supply capacitors
« on: September 23, 2017, 09:16:49 PM »
So I just purchased a Roland GR300 and opened the thing up to check the power supply capacitors.

According to Wayne Joness GR 300 site the blue tantalum capacitors of that era are known to fail, and he recommends replacing them.

Well sure enough inside my GR300 is a burned blue tantalum capacitor. Well someone must have known because that capacitor was disconnected from the circuit on one of its leads.

Next to that capacitor at C28 is a resistor marked brown black yellow silver (the yellow looks gold but I assume it's yellow because it's a multiplier band), that is also charred on the surface.

I think the charring may be from the burned capacitor, but I will replace that anyway but I need someone to check my work.

I get the value of that resistor at 100K ohms plus or minus 10%.

What I don't know is if this is a carbon or ceramic resistor. In addition I don't know what wattage rating the thing has. What should I order?

When I checked the voltage at the + -15 volt leads, as Wayne Jones recommends,and get a voltage of 14.9 volt for both plus and minus leads.

And the machine works just fine with that capacitor disconnected. Why would that be so?

I purchased the thing from a pawn shop off of reverb.com and I have a warranty of 30 days but I would rather just fix the thing because there's no guarantee that the next one won't also have issues and fixing the thing will be fun.

From the pictures it looked like it was an excellent condition.

Any help or knowledge would be appreciated.



« Last Edit: September 23, 2017, 09:26:40 PM by chrish »

Offline chrish

Re: Replacing GR 300 power supply capacitors
« Reply #1 on: September 23, 2017, 10:16:24 PM »
Top picture is from Wayne Joness site that shows the resistor and the capacitor.

I just did some reading on capacitors and my assumption is this capacitor keeps AC current from bleeding into the circuit?

The bottom picture is from my unit. the burned capacitor and damaged resistor is at C28. And you can see where  one of the capacitor leads  was cut.That thing must have been smoking or on fire.
« Last Edit: September 23, 2017, 11:52:44 PM by chrish »

Offline GuitarBuilder

Re: Replacing GR 300 power supply capacitors
« Reply #2 on: September 25, 2017, 10:58:22 AM »
Top picture is from Wayne Joness site that shows the resistor and the capacitor.

I just did some reading on capacitors and my assumption is this capacitor keeps AC current from bleeding into the circuit?

The bottom picture is from my unit. the burned capacitor and damaged resistor is at C28. And you can see where  one of the capacitor leads  was cut.That thing must have been smoking or on fire.

Hopefully the TA7179 is not fried; that would be a major bummer.  Check the schematic (you can get it from Wayne's site) - the caps are 16V.

Offline chrish

Re: Replacing GR 300 power supply capacitors
« Reply #3 on: September 25, 2017, 11:36:41 AM »
Thanks. I tried to download that  information at the Joness site to my phone but it didn't work so I guess it's off to the library to use the computer there.

Yeah I'm hoping something else didn't get fried but the unit does work so I'm hopeful. The voltage still measures plus and minus 14.9 volts with that burned capacitor removed from the circuit but I don't know if that's an indication that the TA7179 is completely working as it should.

I did find out from the Mousers Tech that I'd be looking for a 1 ohm resistor because that third band can be gold. But he still needs to know the wattage so hopefully I can get a parts list from the Joness site also.

I found some information that said that the resistor wattage is related to physical size and it's 5mm, but that didn't help. It also seems like it must be a carbon resistor cuz it sure resembles those ones that I smashed up when I was a kid. :)

 I also dropped in on mr. Carlson's lab on YouTube to check out some capacitor removal and soldering techniques. The one thing that concerns me the most with my own inexperience is  dwell time with the soldering iron.

I also know now that the word is pronounced sol-der-ing not sod-ering. :)

The whole process is very educational.

It would have been cool if High School offered it course where we could have built a fuzz tone pedal but I guess reading The Grapes of Wrath seemed more important to the educators.

Offline Elantric

Re: Replacing GR 300 power supply capacitors
« Reply #4 on: September 25, 2017, 12:03:10 PM »
Quote
It would have been cool if High School offered it course where we could have built a fuzz tone pedal but I guess reading The Grapes of Wrath seemed more important to the educators.

Luckily when I was going to school, I was able to take Electronics class in both 8th grade and 9th grade (1968 / 1969) - and yes - I built a Heathkit Fuzz box along with a crystal radio

start here
http://www.joness.com/gr300/service/G-303_G-808_GR-300_SERVICE_NOTES.pdf

Quote
Hopefully the TA7179 is not fried;
They are AVAILABLE here:
http://www.ebay.com/itm/TA7179P-TA7179-TOSHIBA-IC-/110826544940

« Last Edit: September 25, 2017, 01:07:44 PM by Elantric »

Offline GuitarBuilder

Re: Replacing GR 300 power supply capacitors
« Reply #5 on: September 26, 2017, 12:13:51 PM »
I did find out from the Mousers Tech that I'd be looking for a 1 ohm resistor because that third band can be gold. But he still needs to know the wattage so hopefully I can get a parts list from the Joness site also.

I found some information that said that the resistor wattage is related to physical size and it's 5mm, but that didn't help. It also seems like it must be a carbon resistor cuz it sure resembles those ones that I smashed up when I was a kid. :)

It says right there on the Roland schematic: 1 Ohm, 1/2 W
« Last Edit: September 26, 2017, 12:20:08 PM by Elantric »

Offline chrish

Re: Replacing GR 300 power supply capacitors
« Reply #6 on: September 26, 2017, 08:43:59 PM »
The gr100 uses the same power supply setup and that half Watt writing appears a little more clearly on that schematic.

Good to know that you can get a generic version of that TA7179L chip.

Since so many of the other chips are no longer available I would wonder if anyone could recreate a new version of the GR300.

I sent spicetone an email and asked them if they were working on any new hex products and was trying to convince them to take a look at the gr 300.

They said no they weren't working on anything and would take a look at the gr300. It would be cool if they could and add  CV out for the pitch tracking.

According to Mark Smart, if I read correctly, the gr 300 didn't have an envelope follower so he designed a circuit for that.

So with the pitch tracking and the envelope follower CV outs, possibilities are open for triggering things like the Moog Slim phatty, the mood Voyager, many other modular synth modules and I believe  the Behringer Model D.

So the question would be, if a new 13 pin version of the analog GR 300 is released, and it captured that Pat Metheny horn sound exactly, would that pedal sell?



« Last Edit: September 26, 2017, 08:47:11 PM by chrish »

Offline chrish

Re: Replacing GR 300 power supply capacitors
« Reply #7 on: September 30, 2017, 05:18:21 PM »
I replaced the burnt-out capacitor today and the unit is working fine. The voltage measures +14.87 and -14.87.

The resistor cleaned up well with a little isopropyl alcohol so that was not replaced. It wasn't damaged it just had some surface char from the capacitor burnout.

The other Blue tantalum power supply capacitor , which is not damaged  at the moment , but will be replaced when I get some proper flux.

The flux I have on hand is meant for soldering copper water pipe joints, of which I've sweated about a thousand or so in my home construction career.

I'm assuming it has something to do with the acidity of the flux and not wanting that sitting on a circuit board?

Fortunately the power supply IC seems to be working fine.



Offline snhirsch

Re: Replacing GR 300 power supply capacitors
« Reply #8 on: September 30, 2017, 05:28:15 PM »
but will be replaced when I get some proper flux.

The flux I have on hand is meant for soldering copper water pipe joints, of which I've sweated about a thousand or so in my home construction career.

I'm assuming it has something to do with the acidity of the flux and not wanting that sitting on a circuit board?

Good instincts.  NEVER, EVER use plumber's flux on electronic gear!  The pH is completely wrong and will definitely cause corrosion.


Offline chrish

Re: Replacing GR 300 power supply capacitors
« Reply #9 on: September 30, 2017, 05:40:37 PM »
Maybe  not so good instincts as I did replace the burnt-out capacitor using that flux.

I did clean the area well before and after but now I'm wondering if I should remove the old solder with the wrong flux and solder in a new capacitor? Or did that Flux mostly burn up. At least the solder had the right core flux.

Electronic solder flux is not so easy to find in these parts.
« Last Edit: September 30, 2017, 05:43:28 PM by chrish »

Online admsustainiac

Re: Replacing GR 300 power supply capacitors
« Reply #10 on: September 30, 2017, 06:04:53 PM »
Use a q-tip and alcohol to remove old flux

Offline gumtown

Re: Replacing GR 300 power supply capacitors
« Reply #11 on: September 30, 2017, 06:29:17 PM »
Maybe  not so good instincts as I did replace the burnt-out capacitor using that flux.
  :o :o :o :o :o :o :o :o :o :o :o :o :o :o :o


Electronic solder flux is not so easy to find in these parts.
Resin cored solder is the correct stuff, the flux is inside the tube-like roll of solder.
Free "GR-55 FloorBoard" editor software from http://sourceforge.net/projects/grfloorboard/

Offline chrish

Re: Replacing GR 300 power supply capacitors
« Reply #12 on: September 30, 2017, 07:30:59 PM »
  :o :o :o :o :o :o :o :o :o :o :o :o :o :o :o

Resin cored solder is the correct stuff, the flux is inside the tube-like roll of solder.
when I ordered the parts I got the right solder, with rosin core flux, but forgot to order the paste flux.

 When I soldered the neon lamp into the ADA power amp the rosin core solder was just disappearing into smoke and the on the board.

So I had some Oakley no.95 flux (aluminum chloride) and placed a minut amount on to the Joint and the solder flowed just fine.

Then I replaced the capacitor in the GR300 the same way.

Use a q-tip and alcohol to remove old flux
that's exactly what I used but I think I'll go over it again just to be sure.



« Last Edit: September 30, 2017, 07:39:54 PM by chrish »

Offline chrish

Re: Replacing GR 300 power supply capacitors
« Reply #13 on: January 07, 2018, 07:55:23 PM »
So I just got another gr300 in the mail and I'm getting a funny smell that seems to be coming from the Transformer.

The voltage after the regulator chip checks out at -14.64 and +14.7 so that seems to be operating within the specs.

Does anybody have any recommendations for testing the Transformer further? Or is it common for those Circa 1982 Transformers to have funny smells emanating from them? It doesn't seem to be getting overly hot.

Also if the Transformer fails, do other circuits down the line also tend to fail?


Upon further inspection and comparing it to the same board in another gr300, both model C, it appears that the one I just got has had some work done on it.

On the main board at IC4, the stock chip is MC 14001 B. One stock chip remains and five of the other chips have been replaced with Toshiba TC 4001 BP.

At IC8 on the new arrival gr300 three of the chips in that position are Toshiba TC 40168 P. On the other gr300 that I've had, those three chip positions are MC 14016 B.

So am I correct that those Toshiba chips aren't just something that Roland may have thrown in there and it really is a  repair? It sure doesn't seem like there would be 5 Toshiba chips and one stock chip.

The other thing I noticed is the electrolytic capacitors are blue on the one I just received and black on the one I've had. I'm guessing that's just what they had that's a factory  for that production run and not a recap job.

No capacitor bulges or leaks are apparent on either gr300.

Any comments or concerns would be appreciated.



« Last Edit: January 07, 2018, 08:02:26 PM by chrish »

Online admsustainiac

« Last Edit: January 08, 2018, 12:35:24 PM by admsustainiac »

Offline chrish

Re: Replacing GR 300 power supply capacitors
« Reply #15 on: January 08, 2018, 12:13:37 PM »
4001 is a common CMOS logic chip
No need for a Roland version

https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.onsemi.com/pub/Collateral/MC14001B-D.PDF&ved=0ahUKEwiP7PPe4sjYAhVkw4MKHd6iALAQFggnMAA&usg=AOvVaw0x7mrCK9Ad5xVde5kGoZ4O
Thanks, that's good to know. Whoever did the replacement work did a really clean job.

 I guess it's important for me to realize that buying this vintage gear is always a risk.

The positive side is I get to use the Fantastic tone, playing feel and expression while it lasts and it's also an educational process.

https://en.m.wikipedia.org/wiki/Logic_gate

"Logic gates are primarily implemented using diodes or transistors acting as electronic switches, but can also be constructed using vacuum tubes, electromagnetic relays (relay logic), fluidic logic, pneumatic logic, optics, molecules, or even mechanical elements. "
« Last Edit: January 08, 2018, 12:17:31 PM by chrish »

Offline chrish

Re: Replacing GR 300 power supply capacitors
« Reply #16 on: January 10, 2018, 12:27:33 PM »
The Transformers smell has  gone after leaving the unit on for an extended period of time.

It still smells but it's more like what a Transformer or how other electronic gear , like old TV's, smells like when their powered up.

 Wonder if an insect could have crawled in there or maybe deox spray was used extensively when the ic chip Replacements were done.

Or maybe the Fix-It Gremlins snuck in overnight. :)

So I'm starting to see why people get disgusted with Guitar Center.

The advertisement for the  gr 300 said that it came with the original box, and that wasn't provided.

I thought that for resale value, that box might be valuable to a collector someday.

They must have felt it was an important feature because they put it in their ad.

I called the store and talked  to the sales person and then Frank the manager. Both said that the box was in bad shape and most likely  thrown away.

They also added that if I'm not happy with my purchase, just to return it.

I asked the salesperson why they threw it away and he says because we don't keep old  boxes around.

 I guess they only advertise old original boxes. ;D

So it's 7 hour round trip drive to my nearest Guitar Center or $150 in shipping cost to return the gear, so that's not likely to happen just because of a box. 

Otherwise the gear appears to be functioning normally.

Do original boxes for vintage gear add value? If so what would that value be?



« Last Edit: January 10, 2018, 12:30:00 PM by chrish »