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TX802 power supply issues

 

Good Evening (Well it is here)

I have some issues with my 802, Some times it would boot and some times I got a initial boot screen and then it would dim.? After a power cycle it would work. However, two weeks ago it wouldn't pass the boot screen.

The circuit diagram gives +5 and +15 however my power board gave 4.6 and 14.3. After tweaking the pot Im now back up to 5/15V however, this took quite a turn.

So This brings on a question why did the voltage drop is it bad caps? and how long can I use this before it start failing again and I need a tweak to Max...

So I recon i have to recap the power supply and replace the large 1W power resistors. Any other pointers?
 

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Not sure where this response is going to end up, but ... I have seen a lot of Yamaha 80's era stuff dying recently. In all cases so far it's the switching power supply they use. In the luck cases I just replaced all the electrolytics and cleaned the brown glue off the board. In worse cases I had to replace other passives. In the worst case there were other parts I could not find and had to make a wholesale replacement of the power supply. Since yours is working, I would suggest replacing all the electrolytics in the power supply. It's inexpensive parts-wise (like, under $20USD). These supplies are switch mode and they run very hot typically. I am NOT a pro-recap person in the least, but in some cases it is required. So far I think I've done a REV7, two SPX90's and a DX7S. I can't remember if there are others or not.

GB

On 11/10/2020 12:46 PM, Gunter Weeks via groups.io wrote:

Good Evening (Well it is here)

I have some issues with my 802, Some times it would boot and some times I got a initial boot screen and then it would dim.? After a power cycle it would work. However, two weeks ago it wouldn't pass the boot screen.

The circuit diagram gives +5 and +15 however my power board gave 4.6 and 14.3. After tweaking the pot Im now back up to 5/15V however, this took quite a turn.

So This brings on a question why did the voltage drop is it bad caps? and how long can I use this before it start failing again and I need a tweak to Max...

So I recon i have to recap the power supply and replace the large 1W power resistors. Any other pointers?

 

Hi,

I had a similar issue and replaced all of the electrolytics on the power supply board, which solved the problem.

jb

Am 10.11.2020 um 21:46 schrieb Gunter Weeks via groups.io <bob.weeks@...>:

Good Evening (Well it is here)

I have some issues with my 802, Some times it would boot and some times I got a initial boot screen and then it would dim. After a power cycle it would work. However, two weeks ago it wouldn't pass the boot screen.

The circuit diagram gives +5 and +15 however my power board gave 4.6 and 14.3. After tweaking the pot Im now back up to 5/15V however, this took quite a turn.

So This brings on a question why did the voltage drop is it bad caps? and how long can I use this before it start failing again and I need a tweak to Max...

So I recon i have to recap the power supply and replace the large 1W power resistors. Any other pointers?





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Bad filter caps may explain what you described so replacing them makes sense. I would leave the power resistors alone.


Op di 10 nov. 2020 om 21:47 schreef Gunter Weeks via <bob.weeks=[email protected]>:

Good Evening (Well it is here)

I have some issues with my 802, Some times it would boot and some times
I got a initial boot screen and then it would dim.? After a power cycle
it would work. However, two weeks ago it wouldn't pass the boot screen.

The circuit diagram gives +5 and +15 however my power board gave 4.6 and
14.3. After tweaking the pot Im now back up to 5/15V however, this took
quite a turn.

So This brings on a question why did the voltage drop is it bad caps?
and how long can I use this before it start failing again and I need a
tweak to Max...

So I recon i have to recap the power supply and replace the large 1W
power resistors. Any other pointers?
 

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Hi Gunter

?

It worked brilliantly for my DX7ii – works as new now?

?

Regards

?

Stu

?
 

Just a quickie,

Ive ordered all the Power supply Caps.

Is it worth re-caping the main board It sounds fantastic No humm etc..

Do I need to replace all the other type of Capacitors too?

Whilst Im doing this I thought I would re-cap my Original 1979 Korg MS20 Had it since new and this is starting to hum and there are a few driy joints on the board which I thought I would re-flow at the same time.


Regards
 

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On the main board, probably not. Some Yamaha things have +-18v on the power supply that is further regulated to +-15 on the main board, but those parts won't be under as much stress as the PSU caps. You could take a look for leakage or swelling on those if you like. I've never personally needed to replace those.

Anything that is suspect on the PSU should be changed. I've had a couple of small signal resistors and ceramic caps on the PSU that were eaten away. You might not know until you start the removal and cleaning of the PSU.

GB

On 11/13/2020 7:22 AM, Gunter Weeks via groups.io wrote:

Just a quickie,

Ive ordered all the Power supply Caps.

Is it worth re-caping the main board It sounds fantastic No humm etc..

Do I need to replace all the other type of Capacitors too?

Whilst Im doing this I thought I would re-cap my Original 1979 Korg MS20 Had it since new and this is starting to hum and there are a few driy joints on the board which I thought I would re-flow at the same time.


Regards

 

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Just a quick question, I replaced the Caps when testing the 5 V side its reading 7V. Ive checked the Switched side and there is a signal on the optical Isolator.
Ive pulled all the Transistors and put them in a Tester and they all read ok
Question, Does there need to be a load on the 5V line before the switching takes effect or Do I need to look further?

REgards

Bob








On 13/11/2020 15:36, Grant B wrote:

On the main board, probably not. Some Yamaha things have +-18v on the power supply that is further regulated to +-15 on the main board, but those parts won't be under as much stress as the PSU caps. You could take a look for leakage or swelling on those if you like. I've never personally needed to replace those.

Anything that is suspect on the PSU should be changed. I've had a couple of small signal resistors and ceramic caps on the PSU that were eaten away. You might not know until you start the removal and cleaning of the PSU.

GB

On 11/13/2020 7:22 AM, Gunter Weeks via groups.io wrote:
Just a quickie,

Ive ordered all the Power supply Caps.

Is it worth re-caping the main board It sounds fantastic No humm etc..

Do I need to replace all the other type of Capacitors too?

Whilst Im doing this I thought I would re-cap my Original 1979 Korg MS20 Had it since new and this is starting to hum and there are a few driy joints on the board which I thought I would re-flow at the same time.


Regards


 

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Hi Bob,

take care with switching power supplies : many of them do not work properly when they are not connected to a load. In some extreme cases, the power supply can even be damaged as it can not regulate properly (the output capacitors can be charged over their voltage limit)

So if you want to test the power supply without connecting it to the synth main board, the best thing to do is to put a dummy load on the main output (+5V in most cases). Loading the power supply at 25 or 30% is enough most of the time to allow the regulation to operate properly (so if the power supply can deliver 1A on 5V for example, adding a 22 ohms/2W resistor is enough to load the power supply. Take care however : such a resistor becomes really hot !)

Benoit

Le 19/11/2020 à 15:59, Gunter Weeks via groups.io a écrit?:

Just a quick question, I replaced the Caps when testing the 5 V side its reading 7V. Ive checked the Switched side and there is a signal on the optical Isolator.
Ive pulled all the Transistors and put them in a Tester and they all read ok
Question, Does there need to be a load on the 5V line before the switching takes effect or Do I need to look further?

REgards

Bob








On 13/11/2020 15:36, Grant B wrote:
On the main board, probably not. Some Yamaha things have +-18v on the power supply that is further regulated to +-15 on the main board, but those parts won't be under as much stress as the PSU caps. You could take a look for leakage or swelling on those if you like. I've never personally needed to replace those.

Anything that is suspect on the PSU should be changed. I've had a couple of small signal resistors and ceramic caps on the PSU that were eaten away. You might not know until you start the removal and cleaning of the PSU.

GB

On 11/13/2020 7:22 AM, Gunter Weeks via groups.io wrote:
Just a quickie,

Ive ordered all the Power supply Caps.

Is it worth re-caping the main board It sounds fantastic No humm etc..

Do I need to replace all the other type of Capacitors too?

Whilst Im doing this I thought I would re-cap my Original 1979 Korg MS20 Had it since new and this is starting to hum and there are a few driy joints on the board which I thought I would re-flow at the same time.


Regards


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