If I remember correctly, there was a big 1980s Yamaha receiver that I worked on that had a poorly designed transistor regulator prone to overheating.
The fix was to mount the TO220 regulator to the actual steel chassis with leads running back to the board.
No, that was the CR-2020. The actual fault was the transistor. Replacing it was the cure - with a different part #. I was doing warranty for Yamaha during those times.
Long leads could easily cause oscillation. In fact, the original 2N3055 was designed with an fT of 19 KHz for use as a pass transistor mounted off board on a heat sink. Lambda was involved in that one I think. If you didn't check with a 'scope, those jobs you did might actually have some oscillation going on. Mounting power transistors away from their drive and bypassing is a dangerous game.
-Chris
Long leads could easily cause oscillation. In fact, the original 2N3055 was designed with an fT of 19 KHz for use as a pass transistor mounted off board on a heat sink. Lambda was involved in that one I think. If you didn't check with a 'scope, those jobs you did might actually have some oscillation going on. Mounting power transistors away from their drive and bypassing is a dangerous game.
-Chris
Chris, I'm not sure of the exact model, we had it for sale in the showroom at the time, years back.
It did look like the CR-2020 though, so maybe it was.
I sold it for $699 restored, and no, it didn't have any oscillations going on. (I always thoroughly test each job)
The customer came in 2 years later and raved about it, and bought a turntable for his employee.
It did look like the CR-2020 though, so maybe it was.
I sold it for $699 restored, and no, it didn't have any oscillations going on. (I always thoroughly test each job)
The customer came in 2 years later and raved about it, and bought a turntable for his employee.
That's cool. But the issue was that the seals on the 2SD234 (I think) were defective and allowed contaminants in. I normally installed 2SD613 in that location. The factory recommendation might have been 2SD313. Basically the same family part with higher ratings and I stocked those.
That was a really nice receiver. I actually have a CR-3020 in pristine condition I'm going to rebuild for myself. Some day. I serviced a lot of CR-2020 and CR-1020 back then.
That was a really nice receiver. I actually have a CR-3020 in pristine condition I'm going to rebuild for myself. Some day. I serviced a lot of CR-2020 and CR-1020 back then.
Today it was a ground loop in a phono amp. There was 5V across the length of one of the grounds!
RE: that boost board I fixed. I'm just impressed that a MOSFET got hot enough to melt the solder but continued to work! What's that about 190°C or so for tin/lead? The max temp is 125°C for the device I think...
RE: that boost board I fixed. I'm just impressed that a MOSFET got hot enough to melt the solder but continued to work! What's that about 190°C or so for tin/lead? The max temp is 125°C for the device I think...
I wonder if it is just possible for the solder to expand and contract with temperature swings. Eventually crack the joint and have some mechanical stress do the rest.
I fixed a plc today for a local farmer, it's running a indoor feeder hanging from ceiling, it's a handheld unit, went out of production in mid 90s, and went bankrupt, no schematics, nothing, was lucky to spot a few cold soldering and a trimpot with two broken legs, also changed the internal li battery 7.2v , old one was dated 2003.
He was happy cause another company told him that he might invest in a new feeding system which ,at cost 100000 dollars.
He was happy cause another company told him that he might invest in a new feeding system which ,at cost 100000 dollars.
A nice Yamaha A-760. An idiot was into it that redesigned the lights for the buttons, botched a channel repair and made it so the relay still closed. It took a few hours to reconstruct the original lighting circuit and modify it to LEDs (Yamaha over complicated it). Then another hour to repair the blown channel and set the amp up. It used those expensive MT-200 case output transistors.
Now it looks like new, nice, sharp (original looking) button lights and it sounds good. The previous technician should be tracked down and shot several times. He caused a lot of destruction and added cost for everyone.
-Chris
Now it looks like new, nice, sharp (original looking) button lights and it sounds good. The previous technician should be tracked down and shot several times. He caused a lot of destruction and added cost for everyone.
-Chris
That's what helped keep me in business at the shop for decades!
The majority of bad joints were with power resistors, under-rated resistors, and overheated transistors.... not to mention poor designs and cutbacks by the manufacturer.
Been there....... done that....... thousands of them!
Ah Chris, I've had PLENTY of those types of jobs in the shop!
Real ball-busters.
And I gotta love those creeps that attempt to do backyard mechanics crap on stereo amps with one blown channel...... paralleling the good channel's output to both output connections!
One customer who bought a "used" receiver wondered why the balance control acted funny, and they didn't hear "stereo" sound at all.
LOL!
A lot of this crap stems from the good old internet and its endless "helpful" blogs.
Replace the seal in the master bedroom toilet today, as it had been refusing to flush for...too long. Had the thing suspended from a belt strap, 4 adjustable straps over a 4X4, one end on a ladder step, the other on the sill of the window behind the toilet.
I'm certain I landed it square and true on the new wax seal. Appeared to compress nicely. No joy - flushes exactly the same way as it did beforehand.
This, I cannot figure out. The exact same model toilet on a branch off the same pipe makes 3 gurgles in a flush; this one, zero. The water just sits there, never even going down. I can make it go down and have done so 50 times using an extra gallon pot, so the line isnt stop-clogged.
There's an inspection cap on the all plastic lines. Evidence of some kind of white adhesive / putty. I tried to turn it, but it wouldnt budge - didnt want to risk tearing out the whole assembly trying to turn it.
Any ideas from the experienced folks here? I'm stumped - though for sure this would fix it!
I'm certain I landed it square and true on the new wax seal. Appeared to compress nicely. No joy - flushes exactly the same way as it did beforehand.
This, I cannot figure out. The exact same model toilet on a branch off the same pipe makes 3 gurgles in a flush; this one, zero. The water just sits there, never even going down. I can make it go down and have done so 50 times using an extra gallon pot, so the line isnt stop-clogged.
There's an inspection cap on the all plastic lines. Evidence of some kind of white adhesive / putty. I tried to turn it, but it wouldnt budge - didnt want to risk tearing out the whole assembly trying to turn it.
Any ideas from the experienced folks here? I'm stumped - though for sure this would fix it!
Check your air vent. You need air behind water for it to flush.
Otherwise sounds like you have an obstruction in the toilet itself.
Otherwise sounds like you have an obstruction in the toilet itself.
I had a dead bird stuck in one air vent that made flushing a chore.
I put it off, being lazy, who wants to go up on the roof?
Once the damn thing rotted out things got much better.
Solution, use a screen over the roof vent.
I put it off, being lazy, who wants to go up on the roof?
Once the damn thing rotted out things got much better.
Solution, use a screen over the roof vent.
Thanks guys - I'll have a look up there tomorrow! Although I did sense a little airflow from the pipe the gasket went around when I had it up on the straps. I wouldnt think to look up there...
Anyone remember the Sony CPD-1302 computer monitor from the late 80's?
There was a small driver board with the CRT socket on it fitted to the base of the CRT. It contained the driver transistors for each of the three color guns in the CRT. Those did not blow. The "5 watt" TO-220 resistor associated with each transistor would either fail, unsolder itself and fall out, or the solder would become brittle and intermittent causing random loss of one color.
Mine was on nearly continuously, and failed during the warranty period, so I took it to the Sony depot in Miami, where it was fixed.....It failed again out of warranty, so I went to the Sony depot for a service manual, where the guy informed me of an upgrade and handed me three "8 watt" TO-220 resistors for free.
"Upgrading" to a higher rated part of the same size without doing anything else does not beat the laws of physics, so the 8 watt part will eventually reach the same temperature that the 5 watt part did. I expected the part to get hot so I did my best to make them fit tight so they would not unsolder themselves. That worked, the 8 watt resistor failed.
I decided that Sony had no clue, and their service depot in Miami had closed down, so I got some new resistors from Digikey, fitted them with small heat sinks and mounted them on the back side of the board since there was no room on the front. That monitor lived on for several more years without being opened again.
I would wind up fixing, or explaining how to fix, most of the Sony monitors for our computer club over several years.
Note that the current trend for through hole resistors is size reduction. You can buy a "2 watt" resistor today that is about the same size as a 1/2 watt carbon comp resistor. If you stuff more power into a smaller part, the laws of thermodynamics still hold. It will get HOT! Better materials allow a much higher operating temperature. Modern no lead solder will handle the higher temps better, but it still sucks, so we DIYers still use lead. Derate these parts more than 50% and give them plenty of clearance, especially in a PC board design.
I do remember the Sony Trinitron's having their share of issues over the years.
Saw a lot of them come in the door for assorted troubles.
Them, and some other TV brands as well, had various CRT board issues.
There were kits put out by our distributors for specific servicing needs that targeted common problems.
One odd, but not surprising fault of the larger Trinitron sets (27 to 32 inch models) was defective cabinet construction.
The plastic case would unexpectedly literally crumble from the weight of the CRT.
Imagine watching tv, and the damn thing would shatter!
This was due to a wrong plastisizer or chemical reaction in the formula when they molded those cabinets.
Yes, I had one of those CPD-1302 monitors. Same issues, so I got rid of it once I saw what the issue was. Didn't fix TV's (thank god!).
The biggest problem with new equipment is thermal management. Test equipment included. Philips Combi-scopes ran that big chip too hot to touch. Didn't buy one for that reason.
-Chris
The biggest problem with new equipment is thermal management. Test equipment included. Philips Combi-scopes ran that big chip too hot to touch. Didn't buy one for that reason.
-Chris