Rhodes Chroma Polaris

I've owned my Chroma Polaris for many years and repaired it many times. This time its different... When I start it up many LEDs light upon the front panel and that's it. Same patter of LEDs every time; no response to playing the keys or pressing any buttons. Not much of a surprise once I get down and dirty inside. The CPU is running, I've scoped address and data lines on the RAM and ROM chips. There is no signal at all on PCS3. I've checked this line for  continuity from the CPU IC to the various spots where it is used and the connection is good This line enables the transfer of data to/from the front panel. So that explains why the FP is not responding. Always at logic HI. This is a processor line.so I figured maybe the 80186 has died or become damaged. I tried a new CPU chip... same thing.

So now I'm like well what could it be?

I have three revs of EPROM firmware and tried all three... same thing. I have a nice O'scope and DVM and some good tools and lots of parts from that era. I have the owner's and service manuals. As I said I've repaired this guy before but this time around I'm not sure what the trouble is. Any Ideas  on what is going on or what I should check next?

Lou

 

Sounds like the CPU is not executing the code properly, or is getting
stuck somewhere waiting for something to happen. I am not familiar with the
structure of the code, but sometimes panel scanning is initiated by an interrupt
to the CPU. Maybe check any external interrupt signals to see if they are pulsing?

Sometimes you can check address decodes and get a feel for whether the CPU
is stuck polling one particular device, waiting for something to happen.

Also, if you have some spare RAM chips, try temporarily replacing them to see
if that changes anything. A bad RAM will prevent proper CPU execution.
Since the Polaris can use two different sizes of RAM chips, you can infer
the minimum amount of RAM needed for it to operate, and only install that much,
then try different chips.

Of course Paul D is the expert on all things Polaris...

Bob

 

Thanks for the suggestion Greg. OK I’m going to calibrate that again just to make sure.

Should I do this under load or with the PSU output disconnected from the main board?

Lou

 

From: chromapolaris@yahoogroups.com [mailto:chromapolaris@yahoogroups.com]
Sent: June-02-18 10:36 AM
To: chromapolaris@yahoogroups.com
Subject: Re: [chromapolaris] Polaris broken.... help!

 

 

Now, I didn't see any mention about adjusting your DC OK threshold as outlined in the service manual.  This totally sounds like the problem!

 

Greg

Sent from my iPhone

On Jun 2, 2018, at 10:13 AM, Bob Grieb bobgrieb@... [chromapolaris] <chromapolaris@yahoogroups.com> wrote:

 

Sounds like the CPU is not executing the code properly, or is getting
stuck somewhere waiting for something to happen. I am not familiar with the
structure of the code, but sometimes panel scanning is initiated by an interrupt
to the CPU. Maybe check any external interrupt signals to see if they are pulsing?

Sometimes you can check address decodes and get a feel for whether the CPU
is stuck polling one particular device, waiting for something to happen.

Also, if you have some spare RAM chips, try temporarily replacing them to see
if that changes anything. A bad RAM will prevent proper CPU execution.
Since the Polaris can use two different sizes of RAM chips, you can infer
the minimum amount of RAM needed for it to operate, and only install that much,
then try different chips.

Of course Paul D is the expert on all things Polaris...

Bob

On Wed, 6/6/18, Gregory Cox adhmzaiusz@... [chromapolaris] <chromapolaris@yahoogroups.com> wrote:

Subject: Re: [chromapolaris] Polaris broken.... help!
To: "chromapolaris@yahoogroups.com" <chromapolaris@yahoogroups.com>
Date: Wednesday, June 6, 2018, 11:52 AM


 












By the way Bob, Lou’s the guy with the problem, not I  ;)
  Anyway Lou, before you set off on a complicated journey,
I would honestly re-examine the DC OK threshold in detail.
 My main argument of why-- sometimes the power supply DC OK
LED comes on when adjusted
but may still need a little more juice in some situations
to work correctly.  Without the correct DC OK setting none
of the digital side will work and the polaris will be
unresponsive with LEDs lit just as you originally described.
 After making a small incremental
adjustment reset the power and see if it helped, then
repeat again to see if any higher adjustment works.



A while ago my polaris appeared to be screwed and
unresponsive but it was a finicky trimmer on the power
supply.  Make sure it’s sprayed with a contact cleaner or
something and readjust as described in the service
manual.



Greg
















On Jun 5, 2018, at 8:13 PM, 'Lou Champagne'
lou@... [chromapolaris] <chromapolaris@yahoogroups.com>
wrote:











I’m down to two 6264 now with nothing to report
after having swapped them around a bit to make
sure.

 
Lou



>>



Are the installed RAMs 6264 types? If so, just two of them
installed is a valid configuration,

so you could remove all but two and swap those out to see if
you have a bad RAM chip. You can see the 

valid configurations and jumper setting in the service
manual.



The service manual mentions that U84 and some other gates
are not used in the Polaris, and this circuitry

was for something that Fender was developing. I think this
is the circuit that was driving PREQ, so 

probably it's OK to be sitting high.



Bob































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