Help: working on a roland w-30, 5 volt rail to ground

[PINKBOY1006]

Hello I have been working on a roland w-30 for the past week or so and one of the things I had to do is solder on a floppy connector. and in doing that I cut some traces and I had to put bodge wires on those and cleared that up, but there is a question I have to ask before I power this on, it is that there is 28.6Ω across the 5 volt rail and ground and I have no clue if that has to do with the 220μ 16 volt electrolytic across ground and the 5 volt rail, or there is something wrong with the circuit or my soldering job. Your help will be appreciated. here is the schematic: http://www.deepsonic.ch/deep/manuals/roland_w-30_service_manual.pdf
Edit: forgot to mention that on the main board schematic what you are looking for is in u-q 20-28

 

[davenn]

whilst I look over the schematics

can you show a sharp and well lit pic or 2 of your soldering etc on the board

 

[PINKBOY1006]

sure,

back of board

front of board

front of board diff angle.

 

[davenn]

hi ya

ohhhh that's scary LOL

have you heard of solder wick for sucking up excess solder and for just tidying up solder holes ?
you need to get some and use it on all those holes that no longer have component legs going through the holes
those ragged solder blobs could be creating the occasional short circuit problem

you have a long loop of bare wire being used for a repair to a track .... shorted that loop, use insulated wire and
reroute it away from all those fly leads .... come down around the other way, where you can see that C2 etc written on the board
it looks like it could be shorting out grey wire connections in a couple of places

in that top pic that grey wire going to the 3rd pin in looks as tho it may also be shorting out to the 4th pin ??


There's just so much tidying up to be done initially before anything else is done

Dave

 

[jgrade]

If I could chime in here with a bit more clarification

We think we have it soldered correctly but when we were checking to make sure the cables were soldered to the correct parts using a DMM set to continuity we found that the +5.3V pads and the ground bus have continuity. Checking for resistance we find 28ohms.

We have checked every solder joint over and over and can't find a short. It doesn't seem right to have continuity between the positive and negative rails. Looking at the schematic around r-21 it looks like positive and ground are connected via a 220uf cap. It seems that this would explain the continuity but I wanted to ask you guys first before I plug it in and watch the magic smoke.

Any thoughts?

 

[davenn]

If I could chime in here with a bit more clarification .....

Any thoughts?

Who are you ?

until the work is done that I commented on in an earlier post ... as there are so many potential problems there,
its not worth continuing. Show me pic of a cleaned up board. To be bluntly honest, many of the solder joints look terrible.
After all that is sorted out and looking good, THEN we can start assessing the possibility of a component failure
I have to assume the unit was working before your modification work on it ? if so then its a reasonably obvious assumption that the problem has been caused my your soldering, and in that area the fault lies


Dave

 

[jgrade]

Who are you ?

I am the OPs father. We were working on the project together.

Some of what you requested is not possible. The bare wire is soldered to a trace and there are not other places to connect it. The other end of the trace is on pin 38 of a 64 pin surface mount device. We tried very hard to solder it directly to the IC but gave up before we really messed things up. Anything with a jacket was near impossible to solder which is why we isolated it with the hot glue. We checked the wire to make sure it was not the short and it is not. Actually the issue came up prior to soldering most of the wires. We found the issue (if it is an issue) after only 3 wires had been soldered. The components legs are all grounds from the old FDD connector. We left them there to not damage the board any further.

We know the board looks bad but if it's functional we would be satisfied. Perhaps it's not clear that we have not tested this unit yet. We were looking for some information prior to plugging it in and possibly causing major damage. The unit did power on prior to the modification but did not work correctly. We did not take measurements prior to doing the work. Live and learn. We are sure the unit will power on but don't want to smoke anything if we caused a short.

What we are really trying to figure out is it normal for a circuit to have continuity between the ground and positive rails when the + and ground are connected by a cap? It seems to me that this may be a normal situation and not necessarily a short. If this is normal then we will fire it up and see if it works.


This is the part of the circuit I think is creating the "problem" It looks like the cap is filtering the voltage and causing the meter to show continuity.

We are both very anxious to fire this thing up hence the reply from me.

Thanks for the help.

 

[davenn]

but there is a question I have to ask before I power this on, it is that there is 28.6Ω across the 5 volt rail and ground

OK, hi there

Back to your original Q .... yes that 28 Ω is a problem and pretty much a short circuit
I would expect the input resistance to be somewhere around the 500 Ω to 1k, maybe a little more
If the capacitor wasn't a problem initially ( prior to mods) then it isn't the problem now
As I have already said, the problem is most likely to be in your mods wiring




the way you have wired that bare wire red hilited is really shocking
instead do the path I have shown in blue ... less than 1/2 the length and use insulated wire

Dave

 

[jgrade]

Well after an exhaustive amount of checking, there were just no spots that were shorted so we fired it up. Sure enough it booted correctly with the floppy emulator. I was a huge PITA but in the end my son is ecstatic that he has a functioning 25 year old sampling keyboard. Now to get the SCSI drive working!

Thanks for the feedback..