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KenO <kenitholson@yahoo.com>: Dec 22 07:45AM -0800 Received a nonworking GPX C971 Cassette/CD Boombox for repair learning experience.   Used DVM to check Ohms on AC and DC connections Both were infinity for power switch off and on.   Am guessing the problem is a blown fuse.   Checked the forum using keywords "GPX C971" got nothing.   Googled using keywords "GPX C971 schematic" also nothing.   Am sure that the the schematic is on the Internet so would be interested in help finding it.   Thanks   Ken

Mook Johnson <mook@mook.net>: Dec 21 05:55PM -0600 On 12/21/2014 2:54 AM, Phil Allison wrote:   > A coin sized device made by "Epcos" that has 6 ohms cold resistance and jumps to circa 20kohms if overheated - and it can tolerate 240VAC.   > So, if the DC supply does not come up in the first 100mS, the PTC goes high and that is that. Brilliant.   > .... Phil   I believe some loudspeakers use that trick in tweeter and midrange crossovers. They called them "polyswitch" to protect them from too much continuous power.   Never used them but saw them referenced in Infinity, Polk and other consumer high'ish' end ($800+/set)loudspeakers of the 90's.

Phil Allison <pallison49@gmail.com>: Dec 21 07:29PM -0800 Mook Johnson wrote: Phil Allison wrote:   > I believe some loudspeakers use that trick in tweeter and midrange > crossovers. They called them "polyswitch" to protect them from too much > continuous power.   ** Been using Polyswitches for decades.   They are not suitable for 240VAC use and have far too low cold resistance values like 0.1 ohms.   The Epcos PTC has 6ohms cold resistance and can be connected directly across the AC supply with NO harm despite dissipating 10kW for a few milliseconds.     .... Phil

Cydrome Leader <presence@MUNGEpanix.com>: Dec 22 05:46AM > ** Its actually rather well made - Crown Audio are not mugs.   > nasty silicone-looking glue   > ** Huh ?   I see a red wire glopped to the board at the ends and sort of cable tied to another brown wire. It makes no sense. Replacing one filter cap will surely tear the PVC sleeve off all the caps touching it. I really hate that glue stuff.   > and sloppy cable ties parts buried under other parts   > ** Not true.   How do you replace the lower right TO-3 transistor in the photo? From what I can tell, you need to remove two more transistors and the headsink that blocks the one buried under it. It's got that build once, service never look and feel.   The output and power wiring look nice though.   >> It is amazing fans cost less than real heatsinks these days.   > ** It has always been so.   If a fan dies in that thing does it go into some sort of protection mode or does it just blow up?     > Turns out, it has a soft start circuit consisting of a relay and a PTC in parallel. No, not an NTC - a *PTC* !!   > A coin sized device made by "Epcos" that has 6 ohms cold resistance and jumps to circa 20kohms if overheated - and it can tolerate 240VAC.   > So, if the DC supply does not come up in the first 100mS, the PTC goes high and that is that. Brilliant.   Interesting. Sounds like a built in version of running TV in series with a light bulb to check for other faults after replacing the horizontal output transistor.

Phil Allison <pallison49@gmail.com>: Dec 21 02:54PM -0800 Tim Schwartz wrote:   > is as his machine is running SLOW, and it the tape is being pulled ahead > by the take-up torque overpowering the capstan/pinch roller, it would be > running fast.   ** But a capstan spinning against a glazed roller will slip and hence not drive it round at full speed.   Most of my recent experience is with Roland tape echoes which use a 5 metre long loop squirming around in a box. Back tension come from pairs of felt pads the tape passes between as it leaves and enters the box.   When the roller is glazed, tape speed is slow and unsteady.   Also, tape becomes slightly sticky with age and grips to the heads as it passes over them - so much so that in some cases the loop will stop moving completely until you lift the tape off the heads and start again. This is the case even when the pinch roller in perfect condition.   The fix here is to clean all the heads and guides and replace the loop.   .... Phil

Colin Horsley <horsley-spam@westnet.com.au>: Dec 22 11:35AM +1100 On 21/12/2014 13:11, Phil Allison wrote:   > As Pete Townshend famously said " .. the simple thing you see are all complicated ... "   > Capice ?   > .... Phil     Excellent description Phil.   Thank you   Col   --- This email has been checked for viruses by Avast antivirus software. http://www.avast.com

Jeff Liebermann <jeffl@cruzio.com>: Dec 21 10:59AM -0800 On Sat, 20 Dec 2014 16:03:27 -0600, "Lee Gleason"   >I'm guessing I have some sort of vertical amplifier problem. Before diving >back into the schematics, I thought I'd ask, anyone ever seen this symptom >before?   These may help: <http://www.eevblog.com/forum/projects/tektronix-465-repair-and-restoration/> <http://www.spurtikus.de/basteln/repair/tek465/index.html>   -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558

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