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ARP Axxe Repair Thread (was Cleaning Vintage (Arp) Sliders)
MUFF WIGGLER Forum Index -> Music Tech DIY Goto page Previous  1, 2, 3, 4, 5, 6, 7  Next [all]
Author ARP Axxe Repair Thread (was Cleaning Vintage (Arp) Sliders)
emdot_ambient
Yep, got the resistor values correct in that. 39.2K and 33.2K. Looked at the PCB just now and with a magnifying glass I can read it written right on the resistors....

....only thing is, when I check the actual resistance coming off them, one's reading 17.69K and the other's reading 17.59K.

I don't know the math of these things. Why'd they use the 2 resistors like that?

Oh, and the high voltage going TO the keyboard from that circuit is actually 2.97, so the issue's definitely in the circuit.
daverj
If the two resistors are in parallel, then it's odd that you got different values when reading each one. They should read exactly the same value.

A 39.2K and a 33.2K in parallel calculates to 17.976K. (if they're 1% resistors then it could be between 17.798K and 18.155K) When tested in circuit the reading might be a bit different because of other components in the circuit. But both of them should read the same, if they're in parallel to each other.

The reason for them to read different could be:

- bad solder joint or corroded trace between them
- loose lead on the meter
- poor connection between meter lead to component lead when reading them
- old battery in meter, so values change over time

You might replace the battery, and then when doing the reading rub the probes on the component leads to make sure you get through any oxide on the leads. If they still read different then I'd check the circuit to make sure they really are in parallel, and to see if the solder joints look good.

One reason a design might have two resistors in parallel is if the target value needed is not a standard resistor value. Putting two in parallel lets you come up with all sorts of non-standard values. Another reason is to increase the wattage.

The other thing to consider is that 2.97v is only 1% off from 3.00v. Many digital volt meters aren't accurate enough to guarantee that 3.00v will actually read 3.00v
emdot_ambient
Thanks for the info! I hadn't even thought about the reading actually showing the parallel value. Makes a lot more sense, though.

I'll look into the battery thing. I think my meter's a Fluke 73-III. I'm not sure the exact model, but it's rated at something like .01VDC accuracy and was supposedly calibrated in the past year. It consistantly shows 2.97, 1.98, .99 and .01 volts on the octave outputs.

I was hoping to use the Axxe's keyboard CV out for some calibration on DIY VCOs, but the current readings would give me -12 to +36 cents off true note value.
IvanC
Arp Axxe's, and a lot of other synths of their vintage, have a bunch of tantalum capacitors that are time bombs. They tend to short when they go bad. I highly recommend going through and replacing all of these before they short and cause damage.

Ivan
frax
Hi!

I have an Axxe and an Oddy im about to freshen up a little and both of them have quite a few sliders broken of.

What options do I have to fix this?



/frax
dougt
I have some of the slider shafts. You will need to desolder the sliders, carefully open them up and replace the shafts.
frax
dougt wrote:
I have some of the slider shafts. You will need to desolder the sliders, carefully open them up and replace the shafts.


PM!
emdot_ambient
After you desolder the sliders, here's a video that shows how to open them up...I haven't tried it but it looks pretty easy:

http://www.youtube.com/watch?v=LpiB5EBB5wo
jarvis
it's very easy to do the shafts, just make sure you don't bend the metal tabs too much. i think they're iron & they seem like they'd snap after a dozen bends or so (which you shouldn't even get near). I just used a q-tip & deoxit on the swiper/resistor plate to clean off the gunk. Might be a good idea to get some fader lube too, but I didn't have any on hand at the time when I did mine
dude
anybody know of where to find the plastic arp slider caps?
valis
Apparently you can still order them from places like Mouser. Check this out:

http://www.marksmart.net/gearhack/arpomni/slidercaps.html

There is a little additional work needed apparently though..


For archival purposes:
Quote:

PART
NUMBER COLOR
-------------------------
10TB001 RED
10TB002 BLACK
10TB003 WHITE
10TB004 BLUE
10TB005 YELLOW
10TB006 GREEN

sanders
dude wrote:
anybody know of where to find the plastic arp slider caps?


You can buy the original tipped slider caps from Mouser; for a long time they carried all of the same colors except white (?), but now, I think they only have 2 or 3 colors available. They're a very tight fit at first, you have to kind of stretch them out or heat them with a hair dryer.

I'm sorry, I don't recall the part number, but I ordered some myself less than a year ago.
dude
i have some leads on the gummy rubber ones from small bear but i was hoping for the hard plastic molded ones that were used on later models (orange) i think.
emdot_ambient
I wouldn't want the hard plastic ones. Mine started falling off within a year of buying my AXXE back in 1978!
dude
emdot_ambient wrote:
I wouldn't want the hard plastic ones. Mine started falling off within a year of buying my AXXE back in 1978!


well while i DO want the arp ones, i see they are very hard to come by. anybody got any leads for any slider caps other than the soft rubber ones?
dougt
I have a few of the wider, hard plastic ARP slider caps for $10/ea. Not cheap but cheaper than the guy on ebay charging $19/ea.
dude
dougt wrote:
I have a few of the wider, hard plastic ARP slider caps for $10/ea. Not cheap but cheaper than the guy on ebay charging $19/ea.


nah that is ridiculous.

i have given up looking for arp style caps and and am on to looking for any caps that might work.
jarvis
'bout time to bring this thread back to life.

I just had my Axxe shipped back to me from a friend and the power transformer ripped out of the power supply pcb in transit zombie They must have dropped the package from the plane to my doorstep...

So, I need to redo the power supply, but can't get exact specs on the transformer. It appears to be the same transformer as the early Odyssey and the Sequencer. By the schematics, the +15v rail comes out of Z1 which is a U6A7723 vReg rated at 150mA, so I'm assuming that's the max current available to the synth. Please correct me if I'm wrong!

I was looking at this Hammond 186C56 as a replacement – 56vct @ 210mA. Can anyone see anything wrong with this or should I bump up to a higher current transformer?

Another option is to just throw a Power-One HAD15-0.4 linear supply in there since you can get them so cheap on ebay, but it would require mounting the shield sideways to the Axxe chassis since it's too wide (4.25" vs the current power PCB @ 3"), which I would be concerned about bending the chassis over time due to the weight of the HAD15-0.4 (2.2lbs).

Another option all together would be to get a power supply board on ebay (like this one) and an appropriate transformer for that. Since there are techs out there that offer power supply upgrade kits, maybe its not a bad thing to beef up the available current for the synth?

Any tips are much appreciated!
Graham Hinton
jarvis wrote:

I just had my Axxe shipped back to me from a friend and the power transformer ripped out of the power supply pcb in transit zombie They must have dropped the package from the plane to my doorstep...


Sorry to hear that, but that's why mains transformers should not be mounted on a pcb.

Quote:

So, I need to redo the power supply, but can't get exact specs on the transformer. It appears to be the same transformer as the early Odyssey and the Sequencer. By the schematics, the +15v rail comes out of Z1 which is a U6A7723 vReg rated at 150mA, so I'm assuming that's the max current available to the synth. Please correct me if I'm wrong!

I was looking at this Hammond 186C56 as a replacement – 56vct @ 210mA. Can anyone see anything wrong with this or should I bump up to a higher current transformer?


Don't use that, the voltage is far too high.
The ARP PSU wants about 28V on the reservoirs so an 18-0-18Vac will be fine.
You will probably find that a dual secondary is easier to source, just join the secondaries in series observing the phase. Although a 723 is used there is an external pass transistor. The ARP PSUs are current limited to 180mA on +15V and 150mA on -15V so you need at least a 15VA transformer, 30VA would be enough. I would use a toroidal type mounted on the base and a fused IEC inlet so that you don't have any exposed mains on the PSU pcb.
jarvis
Thanks, Graham!

So this Triad transformer should do the trick? 25VA, dual 18v secondaries.

I think the breakaway of the transformer happened on the very last leg of the trip, as there is – thankfully – no other internal damage due to the transformer rattling around. That could have been very, very ugly...
Graham Hinton
jarvis wrote:

So this Triad transformer should do the trick? 25VA, dual 18v secondaries.


Yes. That type is made by many companies internationally so there will be no problem if you ever need to replace it. As this one has stranded leads (some have the windings brought out--avoid those) you can crimp 1/4" fastons on each lead and repurpose the four faston tabs on the pcb, link them to where the secondaries were soldered in.

btw, I have an Axxe pcb cannabalised for parts. If anybody needs the rare Transpose or Keyboard Repeat switches PM me.
sneak-thief
Re. toroids in Arps:

I replaced a burned out transformer on a MkIII Odyssey last month (it was set to 110V and someone gave it 240V - the fuse didn't save it).

Anyhow, the inrush current of a larger toroid spiked above the original spec'd 1/8A fuse and would blow it. You might need a larger fuse or slow-blow to prevent this (as I did).
onewheeltom
Just received an Arp Axxe (first gen) in the mail from a friend. Picture is attached. Have opened it up, but not powered it on. It was in an Anvil road case with this deteriorating blue foam. I've blown out much of the gunk. The sliders do not move.

I'm thinking first, give the PCB and keyboard a bath and dry. Then test the power supply before re connecting it to the PCB. Any other precautions to take before powering it back on? Sounds like I should have some slider lube on hand before I give it a bath.

This thread is awesome. Lots of great info.
schmidtc
nice axxe! moog filter! never understood why there's bad teeth in the keys of these, seems they'd all age the same. prob best to give it all new big and small electros in the power circuits and then bath it. watch out if there's a big paper tho, don't take kindly to water. really really hot water then a bit silicone lube should get the sliders moving.
jarvis
I have the same 2810 model with yellowed keys but I was able to get rid of most of the yellowing. The base plastic is still slightly off-white so they don't all perfectly match, but it's still a hell of a lot nicer to look at!

I just followed the tips from this video:


I don't have a UV lamp and it's been cold/overcast in Chicago so I was not able to set them outside in the sun, however a few days by the window worked just fine. I used a pyrex baking dish, a 90¢ paint brush from Home Depot, a 4oz bottle of the Sally Salon Creme (~$2), and some plastic wrap.

Take the yellowed keys off the Axxe, wash off the grime, set them in the pyrex dish, coat them liberally with Salon Creme using the cheap paint brush, then cover the dish with plastic wrap so that the creme doesn't dry out so fast. Set it by the window and in a few days your keys will be nearly white!
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