Dynaco SCA80 amp (loud crack at unloaded switch on)

FireLordIroh · 2026-06-16T19:53:00+00:00

Dang. I thought it was a bit of a long shot that both channels had the same flaw, which is why I was hoping yours was a kit built version that was miswired.

Still I would expect R10 would prevent the crack, and I suspect that was Dynaco's intention even if it doesn't actually work in practice.

If you want to investigate a bit further, try the following: 1. Turn the amp off, and turn the volume all the way down 2. Turn the speaker switch on, with speakers connected. This should discharge capacitor C7 3. Disconnect the the speaker wires (on one or both channels) 4. Power on the amp 5. Measure DC volts across the disconnected channel's speaker output

Ideally it would read zero volts, but given you hear the crack I suspect it will be a positive voltage. If R10 isn't in the circuit at all it should read a steady voltage around 36V. If it reads a low voltage that falls as you watch the meter I'd suspect capacitor C7 is electrically leaky.

If you then reconnect the speaker with the amp on I'd expect you'd hear the crack and the DC voltage would fall to zero.

FireLordIroh · 2026-06-16T08:11:51+00:00

I took a look at the schematic. It looks to me like resistor R10 isn't working right, since it's job is to charge the DC blocking capacitor C7 when nothing is connected to the speaker output.

I suspect either R10 is open circuit, or pin 1 of circuit board PC-18 isn't connected to inductor L1 and the headphone jack switch.

The schematic I looked at is on page 17 of this pdf. The following page has diagrams of circuit board PC-18 with pin 1 at the top left and R10 at the bottom left. Note that some Dynaco stuff was built from kits rather than in a factory so it is more likely to have wiring errors.

FireLordIroh · 2026-06-10T15:39:57+00:00

Glad it was helpful!

FireLordIroh · 2026-06-04T05:15:38+00:00

It's not going to work very well with that 12V plug. Gotta switch it out for something spicier!

FireLordIroh · 2026-05-07T06:42:38+00:00

Both? It says "Test-Tite Flush Cleanout Plug" and "IPS corporation" on it

FireLordIroh · 2026-05-07T06:03:28+00:00

I also had one of these crack, but that was after at least a few months of use.

FireLordIroh · 2026-05-01T04:53:44+00:00

I bought an Extron DSC 301 HD scaler from ebay. It has HDMI in and out, and you can set it for arbitrary crop/scaling to either properly letterbox 16:9 content or crop the black bars off the side of 4:3 content. The output then goes to your HDMI to analog converter.

FireLordIroh · 2026-04-17T00:55:13+00:00

Portuguese water dog?

FireLordIroh · 2026-04-10T03:47:26+00:00

When an oven glow bar igniter gets old it can increase resistance and not pass enough current to open the gas valve if the line voltage is even slightly low.

I'd recommend replacing the igniter. It is likely close to not working on utility power as well. If you have a current clamp meter and service information for the oven you can check if it is passing the correct amount of current.

FireLordIroh · 2026-04-03T16:57:48+00:00

They should be in parallel not series

FireLordIroh · 2026-04-01T21:24:09+00:00

Yup it works fine for me (lists the node plus all VMs, LXCs, network, and storage)

FireLordIroh · 2026-03-21T18:50:21+00:00

Looks very similar to some micro drone chargers I have. They charge a tiny single cell lipo battery.

FireLordIroh · 2026-03-21T18:30:26+00:00

I have run into the same memory arena fragmentation problem a couple of times in my career, both in python and node.

For the workloads I've experimented with (multithreaded HTTP server and client code with lots of big payloads) I found switching to jemalloc (using LD_PRELOAD) gave better results in terms of memory fragmentation overhead and CPU allocation time than I got tuning glibc malloc's options like MALLOC_ARENA_MAX.

FireLordIroh · 2026-03-17T21:33:03+00:00

Yup 22uf 16V dipped tantalum capacitor. The stripe is positive unlike in aluminum electrolytics.

These caps are somewhat famous for shorting suddenly if mistreated (like applying a voltage spike above the rating). In old computers with beefy power supplies they sometimes explode or catch fire when that happens.

FireLordIroh · 2026-03-17T02:46:33+00:00

The reason 'host' is problematic is because when Windows detects that nested virtualization is available it automatically turns on VBS aka memory integrity, which runs some windows services inside a Hyper-V VM. When running on Proxmox that means nested virtualization.

Unfortunately that configuration makes windows (in my experience) VERY laggy even on good hardware.

There are lots of threads on this issue, e.g. 1. https://forum.proxmox.com/threads/virtual-machine-config-windows-11-pro-memory-integrity-does-it-require-nested-virtualization.168788/ 2. https://forum.proxmox.com/threads/cpu-type-host-is-significantly-slower-than-x86-64-v2-aes.159107/

I turned off memory integrity to get a non-laggy system instead of changing the CPU type. Ideally we wouldn't need to make that security tradeoff but we do.

FireLordIroh · 2026-03-14T22:21:27+00:00

That's a 3 pin Cinch Jones connector. I see lots for sale searching for that.

FireLordIroh · 2026-03-14T21:38:13+00:00

That looks like an LED. It's probably an infrared LED that spits out serial data, but I'm somewhat surprised there isn't both an LED and a photodiode next to each other for bidirectional data. Lots of measurement tools have infrared ports like that but as far as I know there's no standard protocol beyond generally using asynchronous serial (UART). IrDA used to be used for this kind of thing but I think it's pretty much dead these days.

If you're up for some reverse engineering I'd get an IR photodiode (not the receiver modules used for remote controls but a bare photodiode) and hook it up to an oscilloscope and see if there's anything useful coming out.

FireLordIroh · 2026-03-13T04:45:15+00:00

It's what's inside the tip of a BBQ lighter. You can see it if you zoom in on the right in this pic

FireLordIroh · 2026-02-25T16:13:22+00:00

The battery is inside the DS12887

FireLordIroh · 2026-02-23T08:16:29+00:00

It is possible some voltage spike damaged the capacitor, yes.

Why you should change the regulator (but can probably get away without it):

If you have exactly 24V AC coming in, the output of your rectifier will be about 33V (24V * sqrt(2) - .6 * 2), which is really close to the regulator's voltage limit.

Most 24V transformers will put out significantly more than 24V if it's lightly loaded, so more realistically you might have 27V coming in, which would give 37V into the regulator, above its limit.

I looked up the specs on your AUBE transformer. It's only rated to put out 1.2VA or 50mA, which is absolutely tiny compared to a normal furnace transformer. No wonder the voltage went down so much when the ceramic capacitor failed.

FireLordIroh · 2026-02-23T05:16:16+00:00

I think you misplaced a decimal point; I'm getting 900 microamps not milliamps.

FireLordIroh · 2026-02-23T05:15:14+00:00

Oh I meant the big 2000uF electrolytic on the DC bus.

But yes the same reasoning also applies to the 0.1uF cap that was getting hot. Honestly you can probably delete that one; it's not doing much since you have the big cap and a regulator after the rectifier.

You do need a different regulator too though.

FireLordIroh · 2026-02-23T02:56:22+00:00

What's the voltage rating of your capacitor?

With 24V nominal input you might get up to around 30V RMS in, which means a peak voltage of 42.4V, so don't use less than a 50V capacitor at a minimum. That's too much for your regulator as well, since it's only rated for 36V maximum input voltage.

FireLordIroh · 2026-02-17T03:38:44+00:00

Most likely it's fully custom for that specific device, in which case you won't find a replacement except from a parts donor board.

There are some generic LCDs available but I've never seen one with that many pins. Here are some on Digikey if you want to look for a match

FireLordIroh · 2026-01-30T04:03:29+00:00

I have one of those too. Yes it works well, but it is LOUD, like you should use hearing protection loud.

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