- Substitution for germanium transistor - 4 Updates
- Yamaha Stagepas 300 miniature 8 ch mixer amp - 3 Updates
- Replacing a BNC input connector on a SR780 FFT analyzer. - 1 Update
| Bob Engelhardt <BobEngelhardt@comcast.net>: Jan 05 11:02AM -0500 I have a Heathkit IP-27 bench supply that I got at the dump. Its problem is that the current limiter doesn't work due to a bad transistor. Unfortunately, the transistor is a germanium one and replacements are $30! I found a forum post where the guy had substituted a silicon transistor (TIP32C) and he said a germanium diode in the base circuit should also be replaced with a silicon one. My question is: why does the diode need to be replaced? Here is the relevant part of the circuit diagram (transistor Q1 & diode D7): http://imgur.com/a/43wmd Thanks, Bob |
| dansabrservices@yahoo.com: Jan 05 08:14AM -0800 If the transistor you need is a DTG600, NTE179 is a substitute and is germanium. I have one in stock if you want it. This is a TO-3 style transistor right? The posted schematic was a bit fuzy, so if I have the part number wrong, please post the correct one. Dan |
| amdx <nojunk@knology.net>: Jan 05 10:38AM -0600 On 1/5/2017 10:02 AM, Bob Engelhardt wrote: > be replaced with a silicon one. >My question is: why does the diode need > to be replaced? Because the current limiting is partially determined by the relationship between the voltage drops of the diode (0.3V) and the emitter / base junction of the transistor. If you change only the transistor to (0.6V) you will probably never develop enough voltage on the transistor to start it conducting. Mikek --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus |
| Ralph Mowery <rmowery28146@earthlink.net>: Jan 05 11:45AM -0500 In article <o4lqlv0s7a@news3.newsguy.com>, BobEngelhardt@comcast.net says... > http://imgur.com/a/43wmd > Thanks, > Bob Without looking, I would say the diode is a form of temperature compensation and the material of the 2 devices should be the same. That would be true if they are mounted on the same heat sink. |
| cr.snow@gmail.com: Jan 05 02:43AM -0800 It's an old thread I know but this seems to be the most useful source of info on fixing these Yamaha units. Having not worked in electonics for a LONG time I'm basing my efforts on what's out there on t'interweb. Seems likely that my unit has the ST P14NF12FP's are blown based on the symptoms and common faults reported so I'm going to try to replace those. Seem easy enough to get hold of the ST P14NF12FP's relatively cheaply from Honkers if you are prepared to wait. I've ordered four of them and will solder them in somehow. Might re-site them on the heatsink though to avoid having to strip a load of components off the PCB mostly buried in mounds of rock hard white suff, presumably epoxy. |
| N_Cook <diverse@tcp.co.uk>: Jan 05 11:53AM > It's an old thread I know but this seems to be the most useful source of info on fixing these Yamaha units. Having not worked in electonics for a LONG time I'm basing my efforts on what's out there on t'interweb. > Seems likely that my unit has the ST P14NF12FP's are blown based on the symptoms and common faults reported so I'm going to try to replace those. Seem easy enough to get hold of the ST P14NF12FP's relatively cheaply from Honkers if you are prepared to wait. I've ordered four of them and will solder them in somehow. Might re-site them on the heatsink though to avoid having to strip a load of components off the PCB mostly buried in mounds of rock hard white suff, presumably epoxy. "non Yamaha" speaker lead ? Also blown fuse-resitors, slabby SMD <>0.2 ohm, plus other Qs blown perhaps |
| cr.snow@gmail.com: Jan 05 06:09AM -0800 On Thursday, 5 January 2017 11:53:24 UTC, N_Cook wrote: > "non Yamaha" speaker lead ? > Also blown fuse-resitors, slabby SMD <>0.2 ohm, plus other Qs blown perhaps Highly probable as it's in a school and had anything and everything plugged into it. I'll replace the likely components piecemeal until it either works or I run out of patience! What's the SMD and Qs? |
| JC <Chipbee40_SpamNo@yahoo.com>: Jan 04 12:36PM -0500 On 1/4/2017 9:31 AM, Jean-Pierre Coulon wrote: > It has a lid with 4 screws, the leftmost beeing blocked by the chassis. > Is the the right procedure? > Regards, Service manual has dissassembly instructions and warnings. www.thinksrs.com/downloads/PDFs/Manuals/SR780Servm.pdf |
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