I just got my ebay purchased Rabco ST-7 all cleaned up, replaced that blasted tracking wheel with a #31 o-ring, new bulbs, and polished her up. I have a couple challenges however, even after digging into the service manual:
1. It takes a while before it actually turns on..30 seconds to a minute after flipping the power switch before it comes to life. I figure that sounds like a capacitor issue, so I plan on recapping. I only see a few electrolytics, including a relatively large one that is marked "470uf 25WV
" I am not familiar with the "WV". Is that simply 25V or something else?
WV = Working Voltage. I recently replaced the cap on my -7 with a 450@35VDV. *MIND* polarity. Generally, electrolytics are within tolerance at +100/-20% of nameplate. I try to screen my replacements a little bit better than that before installation.
Rules-of-thumb: Try to stay within 20% high to directly at the OEM capacitance. Try not to go more than three times the working voltage on the voltage.
The on-delay could also be from a tired rectifier in the power-supply.
2. The belt that drives the linear tracking mech (looks like a giant o-ring) has a hitch in it from sitting in the same position for what I assume is many years. I hear a squeak every time that hitch goes over the drive wheel. I have not been able to find specs on that belt. Anyone know if there is a replacement out there?
Any industrial supply house will sell you an O-ring. And there are more than a few sources on-line that will sell you all sorts of O-rings in all sorts of materials. THey are cheap enough so that you may order half-a-dozen of slightly different sizes - when you find the ideal size, then order it in some exotic material if you wish - also cheap. http://www.elderrubber.com/orings.htm
is one source that has what you need.
3. When the arm drops onto the LP, it falls to left (leading). I know how to adjust the Lead/Lag, and have that dialed in nicely, and it straightens out in a couple seconds in since I have it tweaked, but again, on that initial drop it falls leading. I have been through the service manual but either I missed it or this condition is not covered. If anyone has experienced this and has any wisdom, please share.
THIS could be two things:
- The first has to do with the arm horizontal bearings not moving evenly. And this can be a PITA to fix. I have been successful in the past by flushing the bejesus out of the bearings with a non-residue cleaner or vast quantities of canned air. Then a tiny bit of fresh lubrication delivered via a fine metal wire to the precise point needed. Not so common an issue.
- The second could be that the arm is not properly vertical in its holder. Often when the arm is attached to the carrier and snugged up, it is cocked very slightly clockwise - or depending on the installer holding it back with excessive strength - counter-clockwise (as you face it). Try turning it back to level - you will get an audible *CLICK* when the arm is centered on the carrier. Look it over carefully from front and back. This issue has been true of _EVERY_ ST-series rabco I have ever seen unless the owner knew of the issue from another source. And the easiest to correct.
By the way - cocked clockwise = lead when dropping. Cocked CC = lag when dropping.
I am completing an arm-transplant - good arm from a cannibalized ST6 plinth to a very nice ST7 plinth with a nasty arm. Lots of niggling adjustments to make yet. But we are very nearly there.
Good luck with it.
Melrose Park, PA
Thanks in advance!