Cassette deck calibration
Back in the day, I can remember using one of these at the local hifi emporium. Other than the Revox and a couple of audio calibrating Nakamichis, I can’t remember a single make /model that didn’t substantially improve after a session on the bench with this gadget. Adjust azimuth, then pop off the top cover for access to PB & record level controls and bias to optimize Fr and distortion performance. Got it down to around 15mins, IIRC.
Back in the day, I can remember using one of these at the local hifi emporium. Other than the Revox and a couple of audio calibrating Nakamichis, I can’t remember a single make /model that didn’t substantially improve after a session on the bench with this gadget. Adjust azimuth, then pop off the top cover for access to PB & record level controls and bias to optimize Fr and distortion performance. Got it down to around 15mins, IIRC.
Attachments
I built up a new 100 watt bipolar amp.
Powered it up and massive crackling noise.
Turned out to be a 5 volt op amp DC servo in a +/-12v circuit !
So pulled it and powered up and got 1Hz square wave on output.
So did a visual inspection first and nothing untoward.
Checked every resistor for correct resistance.
Checked every transistor using diode check.
Powered it up and checked all voltages and they looked ok.
So pinched the right op amp from another amp.
Circuit now works ok.
I looked at the circuit diagram and if the op amp isnt fitted there is a path from output through 1 meg resistor through integrating cap through a 47k resistor into input of ltp.
This caused a positive feedback path and oscillation.
Powered it up and massive crackling noise.
Turned out to be a 5 volt op amp DC servo in a +/-12v circuit !
So pulled it and powered up and got 1Hz square wave on output.
So did a visual inspection first and nothing untoward.
Checked every resistor for correct resistance.
Checked every transistor using diode check.
Powered it up and checked all voltages and they looked ok.
So pinched the right op amp from another amp.
Circuit now works ok.
I looked at the circuit diagram and if the op amp isnt fitted there is a path from output through 1 meg resistor through integrating cap through a 47k resistor into input of ltp.
This caused a positive feedback path and oscillation.
Hi Chris,
Yes, the Sound Tech unit. Flashy. I used just check points, but could easily sweep for frequency response if needed. The new gear I have can sweep, but by using DSP methods. Much faster.
Repaired the voice mail unit. The problem was corruption of some message files that the unit couldn't deal with. It disables the serial port until it figures it is ready, so the fault was a software "feature".
-Chris
Yes, the Sound Tech unit. Flashy. I used just check points, but could easily sweep for frequency response if needed. The new gear I have can sweep, but by using DSP methods. Much faster.
Repaired the voice mail unit. The problem was corruption of some message files that the unit couldn't deal with. It disables the serial port until it figures it is ready, so the fault was a software "feature".
-Chris
At the shop in involved, the machine was set up on a table in one of the front window cubbies, where customers could sit and partake in the sacrament of “calibrating for the particular type of tape you’re using”, while sipping a freshly brewed espresso or Americano - although it was generally BYB - bring your one biscotti. Also in the same bank of cubbies was the turntable/tonearm set up station, including the rig for adjusting suspension on those fidgety Linn LP12.
Ah, those were the days
Cheers, Terry / Donny
Replaced the memory back-up battery in my Hafler SE130 AM/FM Tuner. Expensive little bugger (Tadiran 3.6V lithium-ion w/solder leads), but since the original battery lasted nearly 30 years I can't complain. I spec'd that battery into the original design knowing it would last a very long time, but always wondered just how long. Now I know, and have no regrets.
Mtn Bike
Did a complete tear down and restoration of a used 2008 Sante Fe Blur mountain bike my wife bought me for my birthday several years ago.
Started it somewhere around the end of March.
Worked with the beat up army green base paint and did a camouflage paint job by hand. Baked it in an old kiln I have.
Rebuilt both the front and rear shocks and gave the front it’s own Camo paint job with new decals.
Completely rebuilt the drivetrain and brake system with new parts.
It was finally completely assembled this past month.
Haven’t had time to tune the shocks and drivetrain yet.
The fall riding season is here, so I hope to get on it this week.
Did a complete tear down and restoration of a used 2008 Sante Fe Blur mountain bike my wife bought me for my birthday several years ago.
Started it somewhere around the end of March.
Worked with the beat up army green base paint and did a camouflage paint job by hand. Baked it in an old kiln I have.
Rebuilt both the front and rear shocks and gave the front it’s own Camo paint job with new decals.
Completely rebuilt the drivetrain and brake system with new parts.
It was finally completely assembled this past month.
Haven’t had time to tune the shocks and drivetrain yet.
The fall riding season is here, so I hope to get on it this week.
Attachments
I should title this post: "What I refused to repair lately"
My neighbor recently purchased a 1987 Tandberg TPA-3016A power amplifier.
Rated power is 440 watts @8ohms, weighs 62 pounds.
Appearance, it's in cosmetically fine condition....looks new, however, the right channel amp is blown, dead shorted.
He said smoke came out of it when he turned it on.
He also paid a mere $500 for it, stated by seller it was in working condition.
Working examples are going for about $1800 and more, original MRSP was about $3800 in 1987. (the "High-End" market)
So I suspect the seller knew it had a problem.
Also, someone was inside the unit, poorly mounted circuit boards, nicked-up screws in places that were not designed to be removed - a sign of a NON-professional putzer with badly worn screwdrivers being in there.
I know the Hitachi mosfet outputs are discontinued - 2SK175/2SJ55 - each channel uses 4 of each.
I also know suitable replacements are of questionable reliability, and this amp has no sensible output protection designed into it (I checked the service manual already).
So, with that, I'm passing this along.
T'aint worth my time.
Besides, he's got a decent McIntosh MC-2100 (105/105W) power amp that's overheating that I'd much prefer to work on later.
My neighbor recently purchased a 1987 Tandberg TPA-3016A power amplifier.
Rated power is 440 watts @8ohms, weighs 62 pounds.
Appearance, it's in cosmetically fine condition....looks new, however, the right channel amp is blown, dead shorted.
He said smoke came out of it when he turned it on.
He also paid a mere $500 for it, stated by seller it was in working condition.
Working examples are going for about $1800 and more, original MRSP was about $3800 in 1987. (the "High-End" market)
So I suspect the seller knew it had a problem.
Also, someone was inside the unit, poorly mounted circuit boards, nicked-up screws in places that were not designed to be removed - a sign of a NON-professional putzer with badly worn screwdrivers being in there.
I know the Hitachi mosfet outputs are discontinued - 2SK175/2SJ55 - each channel uses 4 of each.
I also know suitable replacements are of questionable reliability, and this amp has no sensible output protection designed into it (I checked the service manual already).
So, with that, I'm passing this along.
T'aint worth my time.
Besides, he's got a decent McIntosh MC-2100 (105/105W) power amp that's overheating that I'd much prefer to work on later.
In the service industry, we've called them "ring joints".
Basically a ring-like crack around the wires on the pad.
Yup. The combination of single-sided PC boards, wave soldering, and inadequate final inspection has paid quite a few bills for me down through the years.
It's funny, at the shop over the years, we'd all agree that "ring joints" were the most profitable thing keeping us in business...LOL!
My sister & her husband lived for many years in a nice house with hot-water heat. When the circulating unit began acting up, the furnace company guy came out & told them they needed all new control boards, plus a bunch of expensive adaptors to connect them to the existing harnesses inside the thing - to the tune of a couple thousand bucks.
I took a look at the original (single-sided) boards and found a large number of cracked joints at the Molex connector pins. Seems like the larger through-hole stuff was always more likely to crack; the wave-soldering process didn't ever seem to get quite enough solder on them.
Anyway, I resoldered everything, put it back together, and it worked fine for years, right up until they sold the house recently. My sis was happy; bro-in-law on the other hand was pissed at that furnace company...
I took a look at the original (single-sided) boards and found a large number of cracked joints at the Molex connector pins. Seems like the larger through-hole stuff was always more likely to crack; the wave-soldering process didn't ever seem to get quite enough solder on them.
Anyway, I resoldered everything, put it back together, and it worked fine for years, right up until they sold the house recently. My sis was happy; bro-in-law on the other hand was pissed at that furnace company...
A lot of home audio equipment suffers from "ring joints" after a while.
Sanyo amps, Sony amps, any brand name, even the highly touted Technics equipment.
It's not because of bad design, it's simply a natural happening due to aging and the heating/cooling/expansion/contraction going on inside these products.
Sometimes it takes out components due to an electical failure - transistors or IC's don't like missing voltages or spikes.
Other times it just shuts down part of a circuit.
I've seen this time and time again over the years.
Heatsinked regulators, power resistors, heavy components, all are suspect.
It was part of what my job was all about daily.
I've seen it all.
Sanyo amps, Sony amps, any brand name, even the highly touted Technics equipment.
It's not because of bad design, it's simply a natural happening due to aging and the heating/cooling/expansion/contraction going on inside these products.
Sometimes it takes out components due to an electical failure - transistors or IC's don't like missing voltages or spikes.
Other times it just shuts down part of a circuit.
I've seen this time and time again over the years.
Heatsinked regulators, power resistors, heavy components, all are suspect.
It was part of what my job was all about daily.
I've seen it all.
It was part of my job, too. Funny thing is that the symptom often inversely related to the nature of fault. For example "no picture, no sound" is usually caused by a dry soldering joint or a blown fuse, both easy to repair. On the other hand, a "minor problem", like distortion or increased noise can take days to pinpoint.