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The question about magnetic tape erase/record circuit

5577 1 Mar 17.2020, 18:10:14

Hi folks - anyone here with knowledge of tape recorder circuitry? I know that tape recorders employ an AC bias oscillator that is mixed in with the incoming signal on it's way to the record head. The bias oscillator also goes to the erase head. Now - I would like to modify a tape deck and add a switch that would disconnect the erase head, while recording, for certain applications. This happens to be in a Marantz pmd-222 cassette deck but the question is more general. Since the bias oscillator goes to both the erase and record heads while recording, will the recording quality be affected if I disconnect the erase head with a switch? I'm looking for a way to cut off the erase function while maintaining quality. ( yes, I do realize that I will get sound-on-sound when I do that) If the two heads are designed to always be there as a required inductive load, then I may have to think of another way. For example, I could get another erase head and place it in another part of the...

Any software tools to create double-sided circuit boards?

4504 2 Mar 16.2020, 18:12:35

I have made one circuit board for a long time, single sided and everything was done by hand. Fast forward to today, and I have several clock circuits I would like to have double-sided boards made for, and I have a pressing project that will require me to finally jump into the water. I bought a vintage unbuilt Heathkit GC-1000 clock kit, and two of the circuit boards are missing. My applications will all be less than 10 KHz circuits. The circuits in question will have DIP's of various sizes, some surface mount components, nixie tube sockets, etc. I don't mind laying all of them out by hand - I don't believe I need a program that automatically does the routing.The first board I need to have made is shown in the attachment - foil from both sides is shown. The board is about 2.6" x 6". I use Photoshop for various graphics design, but my guess is I need a custom piece of software that manages multiple board layers, trace routing, hole sizes, etc. I have no idea where ...

Square holes on aluminum... how do you do it?

1998 1 Mar 13.2020, 02:11:57

I am placing one of my project in an aluminum rack case. Front panel is 2mm, top and bottom is about 1.5mm, and sides are 3mm. I do not own any mechanized tools. All hand tools, bench drill press, and manual tools. I just broke my dremel. I always disliked making non-round holes. But for RS232C (9 pin) and power connectors, square holes are necessary. My usual method is draw out the outline, drill holes inside it along the line, use whatever is available to connect the holes, then file, file, file.... It's time consuming, and prone to slips to cause cosmetic problems. I can do pretty precise crafting but boy - it takes time..... Does anyone know a better way? What I've already excluded are farming it out to pros, buying mills, and hydraulic punches.

Anyone who knows the strange burning on main PCB?

3990 1 Mar 11.2020, 21:31:19

There are some building management product PCBs that look interesting. first up, they are certified products, and from an install in a ceiling of a commercial building (in a bathroom) . There are 2 units from one bathroom that have both failed this way, but other units in the building haven't. they are powering LED lighting ballasts (if that's the correct term?) looks like about 300mA is drawn from each device when on and the devices are nominally rated for 800mA continuous load. Secondly the mains circuit here is a SSR mains switch... not much to it really, but there's an SSR switching active that has a MOV to neutral, and a snubber (50R, then 33nF mains rated film cap) also to neutral.. switched mains also has an NTC in series to the output of the device, to limit switch on current. the NTC is right up against the snubber cap. the PCB is a 4 layer job with what seems to be prepreg/core/prepreg stackup. measures as a nominal 1.6mm thickness spec. obviously inner layers all clear of me...

LED polarity went wrong in PCBA Fabrication

2394 1 Feb 29.2020, 23:09:21

Hi all...the 2 SMT 0805 LEDs on the red layer are in parallel but opposing polarities. They have a common 2.5V but are driven by a Low or Hi digital 5V signal to select which one lights. The thru hole LED placement is a DNP item which I have as a bicolor LED option. Now the PCBA manufacturer installed both SMT LEDs in parallel , same polarity so I cannot select which one lights independently. I note the tplace layer shows 2 square dots close to the centre point with orientation info. So I don't know which file in my gerbers to locate what went wrong. Can anyone give advise?

Any guides about PCB Connectors

2212 1 Feb 28.2020, 19:36:00

Hello I am making a PCB Board whose input is 50V(dc) and 40A(dc), and output is 600V 4 A. I am not sure how to connect my board through external wires from power supply and to load. Please someone guide me how to select connectors. Thank you

How to get circuit results outputted from LTsice?

2106 1 Feb 27.2020, 00:09:13

Hi, I wish to run LTspice simulations, and then automatically get an output from which the eg power dissipated in the mosfet in watts. Eg in the attached simulation, “V(N007,N009)*Id(M1)+V(N006,N009)*Ig(M1)” is the mosfet power in watts, how can I get the simulator to automatically spit this number out after the SIM is run?

The question about PCB stencil, hand assembly

2603 1 Feb 25.2020, 22:40:34

I have made some boards recently and was a little dismayed at the amount of extra solder i managed to get on TQFP parts and the bridging I ended up with. I am also due to redo a design with VQFN on it where much trouble has had on the first version. So other than picking the thinnest stencil, how can I try to correct my over pasting in prototyping without affecting manufacturing? I can obviously pick the thinnest stencil available which is usually 100μm versus the usual 120-127μm but that does not take much off. For example the 64 pin 7x7mm TQFP in Kicad has stencil apertures the same size as the pad. I thought usually some clearance was given? what i can do is to use the back solder past layer to set custom hand assembly apertures.

How to layout a circuit on a perf board quickly and efficiently?

2238 1 Feb 23.2020, 00:23:10

I'm currently building a few Arduino controlled battery capacity checkers. Each one is capable of testing 3 cells at a time and I searched for a long time trying to find the best solution. I finally found one that was the simplest and did more than one cell at a time. I currently have built one of them a perfboard and the circuit works great. The problem is is that it took me two whole nights to wire it all. Last night I tried to reconfigure it to make it easier but I'm not having any luck I just keep thinking and trying and redoing it. I thought about using perfboard layout application to help but that takes a long time also...Does anyone have a way to consolidate the perfboard layout to make it easier and faster? I need to start testing cells as soon as possible and don't have a week or two to build a few of these. I was thinking about doing that dead bug technique I think it's called and just soldering components to each other but the more I think about it the more I keep thinking i...

Any thoughts about SMD right angled PCB connectors

2528 1 Feb 20.2020, 22:26:31

I'm trying to find a decent, cheap, method of connecting a PCB into another at a 90 degree right angle. Ideally the connector has to be SMD (I've no idea if SMD and hole-through can be soldered by machine but I figure it's more work as the piece would have to be glued). My inital thought was something like what PCI or the old ISA slots use, something like that, just a bit more compact. Ideas!?!

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