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What did you last repair??
What did you last repair??
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Old 20th September 2019, 11:08 PM   #221
nigelwright7557 is offline nigelwright7557  United Kingdom
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Quote:
Originally Posted by wiseoldtech View Post
One of my customers complained to me about his flat screen TV repair job estimate.
He brought the thing in, had missing/loose screws on the back cover, and inside the main fuse was wrapped in tinfoil.
Go figure.
I have sold on a couple of IGBT amplifiers.
The buyer managed to blow both up.
He asked for parts list so he could replace the IGBT's.
My reply was little point if the amplifiers are blowing straight away.
You need to find the root problem before replacing parts.
Its unusual for a transistor to just "blow up", especially when new.
Its even more unusual for two amps to blow up in a short time.
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Old 21st September 2019, 02:13 AM   #222
wiseoldtech is online now wiseoldtech  United States
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Well Nigel, since those amps use mosfets, I suppose they're more prone to being sensitive and require careful and proper connection.
Fools usually don't have the learning about them, and then the problems start.


Personally, I don't care for power mosfets in outputs -too touchy.
I'll stick with Old School design BJT in that case - much less worry.
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Old 21st September 2019, 02:28 AM   #223
PRR is online now PRR  United States
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Originally Posted by Jim the Oldbie View Post
......was pissed at that furnace company...
On a lower level: my oil-burner kept kicking-out on flame-(no)detect at start-up. Had the plumber's helper in several times. Obviously weak spark was a suspect. But he had a "coil tester" which read the spark-coil as "good". Each time he meticulously adjusted the electrodes, and it started, for another month. I suggested his tester only "saw" the 120V side, and the 30KV side could have leakage which might not be detected. I also specifically asked for a new spark-coil. Several times!

Finally it kicked-out AGAIN and I went to HomeDepot and got a replacement. This is a Standard part, except the new are SMPS-type and a LOT lighter than the 10 pound iron lump of yore. Fired right up and ran 2 years without fail. Not carrying a sparker on the truck, or at least back at the shop, is stupid.
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Old 21st September 2019, 06:37 AM   #224
wiseoldtech is online now wiseoldtech  United States
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Speaking about home heating systems, around 2009 I converted my 2002 Crown "Aruba" boiler (hot water radiator heating) from a standing-pilot to electronic ignition with a kit by Honeywell.
Apparently, Crown offered it as an option, but the previous owner didn't bother.

It was relatively easy for me to do, and not burning a pilot 24/7/365 does save on gas.
The system has been trouble-free since installation.
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Old 21st September 2019, 07:01 AM   #225
Jim the Oldbie is offline Jim the Oldbie  United States
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Originally Posted by chrisb View Post
Jim - that sounds like a Louis Rossmann type of story, but with less colourful NYC language.
Well you know, just trying to keep it within standards & practices here...
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Old 29th September 2019, 05:04 PM   #226
Pano is offline Pano  United States
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What did you last repair??
Last thing repaired? This thread. A clean up of much over-quoting,
Help keep our forum clean! Don't quote the entire post just above yours. Please read the guidelines just under the forum RULES.
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Old 30th September 2019, 02:25 AM   #227
anatech is offline anatech  Canada
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What did you last repair??
Just rebuilt a little Dynaco PAS-2 preamplifier. Due to it's age, almost every single resistor had to go (carbon composition). Also every capacitor except the multi-section electrolytic (go figure, it's in perfect condition).

The customer wanted it to perform the best it possibly could, so I opted for the best capacitors I could find without an audio name-brand on it. I didn't expect that great an improvement, but it really performed well.. I also matched the capacitors and carefully measured and padded the precision ones for the phono EQ.

If it were my preamplifier, I would have designed a nice high voltage regulator for it. Otherwise its a happy little "keeper". Here is the performance at 1 volt rms output. Not bad considering it was full of mystery tubes!

-Chris
Attached Images
File Type: jpg L THD 1 V after upgrade.jpg (165.9 KB, 118 views)
File Type: jpg R THD 1 V after upgrade.jpg (169.1 KB, 117 views)
File Type: jpg L IMD 1 V after upgrade.jpg (168.7 KB, 113 views)
File Type: jpg R IMD 1 V after upgrade.jpg (172.0 KB, 113 views)
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Old 30th September 2019, 02:31 AM   #228
nigelwright7557 is offline nigelwright7557  United Kingdom
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Went out to the car on Sunday and dead as a dodo.
Wouldn't let me in and no flash of lights or click of door lock when I pressed the key fob.
So went and got my spare key and that didnt work either.
No keyholes on this car so that was the job knackered.
Put a note on facebook the car was dead and my son said some cars have a plastic hatch covering a normal keylock.
Eventually found that and it took an hour to get it off. You have to pop your key in a hole and jiggle it about to get the plastic hatch.
I opened the door and no interior light so that was a bad sign.
I put key in ignition and completely dead.
The only thing that was barely lit was the seat belt indicator on top of the dash.
I then remembered from many years ago I had an old battery charger.
So I found tha tand hooked it up to the battery.
Stuck it on 12 amp range and left it for an hour.
The door locks now work.
I will give it until morning then see if it starts and check to see if battery is being charged by the alternator.
A bit disappointing but its only second time I have had trouble in 3 years from new.
Last time was a battery problem but at least it started and they fitted a new battery free of charge. Its out of warranty now so it will be to pay for this time if its that and not the alternator.
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Old 30th September 2019, 02:35 AM   #229
kevinkr is offline kevinkr  United States
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What did you last repair??
MX-50N again... Well it was a pretty challenged machine that got wet and had some odd issues that surfaced after about 50 hours of run time.

The capstan motor is a direct drive servo controlled BLDC with a logic and op-amp based control circuitry. Turns out I missed a few electrolytics during the overhaul and apparently there was a possible cold solder joint in one of the servo gain selection transistors.

It decided not to run at 15ips, for a while it was intermittent, and then it just started running backwards at maximum speed (30ips).

Surprisingly quick fix and the motor runs much quieter now on both speeds.

Performed the adjustment procedure in the manual. Pretty simple. Was marginally needed on the 15ips setting and also touched up the master clock.
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File Type: jpg 15ips dutycycle adjustment.jpg (75.3 KB, 113 views)
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Old 30th September 2019, 02:37 AM   #230
anatech is offline anatech  Canada
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What did you last repair??
For comparison, here is a Counterpoint SA-3.1 that I completely redesigned both the LV and HV power supplies in. You can see the huge difference a good power supply can make.

The factory power supply was so bad there was no question about repairing it. You could only design a new regulator PCB and carry on that way. The old one had the regulator pass transistor perched exactly on the SOA curve line. I could go on, but suffice to say that the heat had to be spread out between at least two devices. This was done.

As you can see, the new power supply is perfectly happy doing it's thing.

-Chris
Attached Images
File Type: jpg L THD -11.1 dBV.jpg (139.6 KB, 33 views)
File Type: jpg R THD -11.1 dBV.jpg (139.9 KB, 29 views)
File Type: jpg L IMD -11.1 dBV.jpg (142.5 KB, 19 views)
File Type: jpg R IMD -11.1 dBV.jpg (143.4 KB, 22 views)
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