- Briggs and Stratton 3.5 hp lawnmower engine problem - 2 Updates
- Tektronix SG 503 repair - 4 Updates
| captainvideo462009@gmail.com: May 25 08:08AM -0700 I apologize if part of this seems off topic but I thought that the electronic component of it might be on. I have this 3.5 horse engine on my old push mower. The engine is about 38 years old now but the mower is used very infrequently so the hours are not that bad. About 5 or 6 years ago I replaced the old OEM coil that used points, with a used newer electronic type that eliminates the points. The mower is on it's third carburetor, gas tank and second deck but it has always started ok. I tried to start the mower this morning and as sure as my wife said, (I hate it when she's right), "You'll never start that old thing", it wouldn't start. Long story short there is no HV spark to the plug. It seems as though the coil is bad again. I was going to hit up a few used lawnmower places to try to get a replacement coil because I have no engine numbers on my machine to look up the part but I was wondering if anyone knows if it's possible to bench test these things. Thanks for any help Lenny |
| tabbypurr@gmail.com: May 25 08:22AM -0700 > I apologize if part of this seems off topic but I thought that the electronic component of it might be on. I have this 3.5 horse engine on my old push mower. The engine is about 38 years old now but the mower is used very infrequently so the hours are not that bad. About 5 or 6 years ago I replaced the old OEM coil that used points, with a used newer electronic type that eliminates the points. The mower is on it's third carburetor, gas tank and second deck but it has always started ok. I tried to start the mower this morning and as sure as my wife said, (I hate it when she's right), "You'll never start that old thing", it wouldn't start. Long story short there is no HV spark to the plug. It seems as though the coil is bad again. I was going to hit up a few used lawnmower places to try to get a replacement coil because I have no engine numbers on my machine to look up the part but I was wondering if anyone knows if it's possible to bench test these things. Thanks for any help Lenny shouldn't be hard to continuity test the coil LT & HT sides. You have a multimeter? Beware, connecting & disconnecting the meter on the LT side can cause a spark on the HT side. NT |
| "Charles" <charlesschuler@comcast.net>: May 24 01:26PM -0400 Just finished working on this old beast. The display was flashing, indicating an open amplitude control loop. The output vernier had no effect. There is an op-amp error amp and it is socketed (741) so that was easy to try first. No joy. Looking at the schematic it seemed the peak detector diodes would be easy to check. Turns out that they are under two covers but still not too hard. One cover is glued down but was easy to pry off. One diode was open. I tacked in a 1N914/1N4148 substitute and amplitude control was regained and no more flashing display. The output at 250 MHz is within 1 dB. Not too bad. To fix it right, I am looking at a MMBD452LT1G. |
| Look165 <look165@numericable.fr>: May 24 07:53PM +0200 A 1N4148 will never be able to work at 250MHz. Rtaher try 1N3595 or equivalent. Charles a écrit : |
| Phil Allison <pallison49@gmail.com>: May 24 09:53PM -0700 Look165 wrote: > A 1N4148 will never be able to work at 250MHz. ** > Rtaher try 1N3595 or equivalent. ** Err - that is a very slow, low leakage diode. ... Phil |
| Phil Allison <pallison49@gmail.com>: May 24 10:00PM -0700 Charles wrote: > To fix it right, I am looking at a MMBD452LT1G. ** That is a dual Schottky. http://www.onsemi.com/pub/Collateral/MMBD452LT1-D.PDF Readily available and cheap enough: https://www.digikey.com.au/product-detail/en/on-semiconductor/MMBD452LT1G/MMBD452LT1GOSCT-ND/3462360 ... Phil |
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