I bought in an old 1980's Maplin amp none working with some bits missing.
Found obsolete parts on ebay.
The amp powered up and I could hear music but badly distorted.
Checked every component on the pcb and they buzzed out ok.
While checking running voltages I kept coming back to one transistor where voltages didnt see quite right.
Then it hit me while I had done a diode check I didnt check if it was NPN or PNP. Some kind previous owner had replaced the transistor with correct package but wrong polarity transistor. Number was rubbed off so that didnt help. Popped in the right transistor and the everything was fine with the world again.
I expect this project to be fully completed by the end of this year.
You need what we call here a 'round tuit'.
Sorry for the late reply - I couldn't find mine.
Spoke too soon, alas. Hooked it up in situ and within 5 minutes off it went again. Sigh.
It's always the very last thing we check. After which we sometimes think, Why didn't I check that FIRST?! Even though the reasons why are (usually) rational & logical - we (usually) take things in order of probability, and I'm thinking varactor diodes are pretty low on that list. Good job tracking it down.
After which we sometimes think, Why didn't I check that FIRST?! Even though the reasons why are (usually) rational & logical - we (usually) take things in order of probability, and I'm thinking varactor diodes are pretty low on that list. Good job tracking it down.
Last edited:
I had a new build power amp not work.
Checked all components and they all buzzed out ok.
So powered it up and sometimes it would burst into life and then other times not work.
So I then did what I should have done first, a visual inspection.
Spotted it, a resistor leg hadn't been soldered at all but had the leg cut off short so it looked at first like it was OK.
Checked all components and they all buzzed out ok.
So powered it up and sometimes it would burst into life and then other times not work.
So I then did what I should have done first, a visual inspection.
Spotted it, a resistor leg hadn't been soldered at all but had the leg cut off short so it looked at first like it was OK.
Not a repair but an installation; one I've been dreading for some time (was postponed due to coronavirus). Let's just say it lived up to the hype.
Yesterday:
*12 hrs. of climbing assorted ladders, including an 18-foot extension leading to a ceiling hatch in mid-air
*Running speaker cables through 110°F crawlspaces, then emerging to 72° A/C (repeat as needed)
*Breathing through a too-well-used painter's mask, the inside of which smells exactly like a dog that needs a bath
*Ridiculously complicated wire pulls (one took 2 hours to go 4 feet!! Grrr)
*Muscle cramps so bad, by midnight I was basically just a 200-lb. charlie-horse
*One bizarre encounter with an unmasked, weird old dude who actually attempted (unsuccessfully) to walk right up to me and shake my hand! Like WTF, have you been on Mars for two months?! Come on, man...
*Finally hit my pillow at around 4 AM after a 3 hr. drive home
This morning:
*Lost 5 lbs. (feels like 20)
*Blood pressure down >10 points
*Not nearly as stiff & sore as this 62-year-old was expecting
*My minor-but-noticeable toothache has taken the day off
*First honest day's work in weeks
*Nice fat invoice to mail to a grateful client
*While I was there, one of my awesome church ladies sewed me up 4 beautiful brand-new masks!! (She was probably grossed out by the one I was using)
Am I staying home and watching movies on the big wonderful 110" screen today? You bet your bippy.
Yesterday:
*12 hrs. of climbing assorted ladders, including an 18-foot extension leading to a ceiling hatch in mid-air
*Running speaker cables through 110°F crawlspaces, then emerging to 72° A/C (repeat as needed)
*Breathing through a too-well-used painter's mask, the inside of which smells exactly like a dog that needs a bath
*Ridiculously complicated wire pulls (one took 2 hours to go 4 feet!! Grrr)
*Muscle cramps so bad, by midnight I was basically just a 200-lb. charlie-horse
*One bizarre encounter with an unmasked, weird old dude who actually attempted (unsuccessfully) to walk right up to me and shake my hand! Like WTF, have you been on Mars for two months?! Come on, man...
*Finally hit my pillow at around 4 AM after a 3 hr. drive home
This morning:
*Lost 5 lbs. (feels like 20)
*Blood pressure down >10 points
*Not nearly as stiff & sore as this 62-year-old was expecting
*My minor-but-noticeable toothache has taken the day off
*First honest day's work in weeks
*Nice fat invoice to mail to a grateful client
*While I was there, one of my awesome church ladies sewed me up 4 beautiful brand-new masks!! (She was probably grossed out by the one I was using)
Am I staying home and watching movies on the big wonderful 110" screen today? You bet your bippy.
Clutch hydraulics in one of my Lotus Elans - new master cylinder, new stainless armored hose, new slave cylinder, new fasteners. Day before - new stainless brake caliper pistons and rebuild kits, new stainless hoses. Day before that - new 21 lb. lightweight AGM racing battery (yikes - $12 per pound of battery). Nice to get these projects moving along, but not earning any money to pay for them!
12 hours...that is just the beginning for some of my jobs especially with multiple faults
Heh. I guess that didn't include the in between times spent reading the manual and contemplating the problem, or the time simply staring at the thing going mental and cursing [emoji28] I really hope that's it because if I find one of these diodes and some other problem rears its head I am done [emoji378]12 hours...that is just the beginning for some of my jobs especially with multiple faults
30mtr Extension reel. Neutral break.
No visible cuts or kinks.
Cut ~1mtr cable off close to reel end (sharp bend into centre of reel) - not there.
Cut ~1mtr off plug end - not there.
Google suggested finding the break by measuring between cores cable capacitance from each end - ratio = length ratio to break. Calc suggested a little over 2m from one end.
Cut this off the cable, had continuity on the remaining 27mtrs.
Fitted new plug (original was moulded on type).
Reconnected at reel/socket end.
Stripped the faulty offcut & found the break.
Question - do cable manufacturers spot weld join the copper cores when they run out?
The only explanation I can come up with is that the 2 ends of the copper core were poorly (ie not) spot welded.
Looking on Google, it is a not unknown faulty for invisible wire breaks in extension reels.
No visible cuts or kinks.
Cut ~1mtr cable off close to reel end (sharp bend into centre of reel) - not there.
Cut ~1mtr off plug end - not there.
Google suggested finding the break by measuring between cores cable capacitance from each end - ratio = length ratio to break. Calc suggested a little over 2m from one end.
Cut this off the cable, had continuity on the remaining 27mtrs.
Fitted new plug (original was moulded on type).
Reconnected at reel/socket end.
Stripped the faulty offcut & found the break.
Question - do cable manufacturers spot weld join the copper cores when they run out?
The only explanation I can come up with is that the 2 ends of the copper core were poorly (ie not) spot welded.
Looking on Google, it is a not unknown faulty for invisible wire breaks in extension reels.
Sennheiser HD437. Fixed the broken 1/8" plug with 1/4" TRS. Not a trivial fix with the cable used, I guess the trick is to have your iron hot enough to melt the enamel finish but keep it away from the outer insulation. Took 2 tries, lucky I had a bag of cheap 1/4" plugs.
Got a used replacement remote for the Samsung DVDP, did the firmware update, and now it's a great universal player that plays everything I put in it. Cleaned the lens on the Pioneer DVDP, but it still can't play everything. I tried quite a few discs and think it's actually a compatibility issue: I think it is failing to play either unconventionsl discs (e.g. DVD-A with 16/44.1), high sampling rate (i.e. >88kHz) or maybe unconventional header information. At least it was free.
Got a used replacement remote for the Samsung DVDP, did the firmware update, and now it's a great universal player that plays everything I put in it. Cleaned the lens on the Pioneer DVDP, but it still can't play everything. I tried quite a few discs and think it's actually a compatibility issue: I think it is failing to play either unconventionsl discs (e.g. DVD-A with 16/44.1), high sampling rate (i.e. >88kHz) or maybe unconventional header information. At least it was free.