Recent Posts

1

General Technical Chat / Re: Relay trigger when voltage above 13v

« Last post by Andy Chee on Today at 01:46:58 am »

I think you’re after a hysteresis circuit i.e. turn on relay as voltage rises above 13V, turn off relay as voltage drops below 12V.

Alternatively, perhaps you’re after a monostable “reset” circuit i.e. turn on relay as voltage rises above 13V, relay remains on until power is removed.

2

Projects, Designs, and Technical Stuff / Re: Corrosion on DIP pins

« Last post by rsjsouza on Today at 01:45:37 am »

Just an additional annoyance: MOSTEK is known nowadays to have a relatively high incidence of memory rot, which renders the IC unusable due to internal degradation even on ICs that are physically in good shape.

That's a problem with mask ROMs like the MK36000.  Aren't the ICs in the photo DRAMs?

I have seen DRAMs fail as well - you can also check a few of the vintage folks (Adrian's basement, 8-bit guy, etc.) comment this as well.

3

Buy/Sell/Wanted / Re: FS [CAN / US] Fluke PM6680B frequency counter / timer

« Last post by fenugrec on Today at 01:38:21 am »

Bump, summer price 400 CAD

4

Test Equipment / Re: SDS800X HD Wanted Features

« Last post by electronics hobbyist on Today at 01:38:11 am »

I wonder how many use these buttons (see picture). You can move the fields by simply dragging them, so i would say these buttons are redundant. They would cover a field that you could otherwise click without moving the fields at all.

Dragging is implicit, while arrows are explicit, and also said that there is information on the left and right, I think this is part of the reasons for retaining the arrow.For first-time users or users of the mouse, this arrow is necessary.

5

Projects, Designs, and Technical Stuff / Re: HP 3478A ROM Dump

« Last post by fenugrec on Today at 01:32:29 am »

The second has an internal ROM.  I don't know if its readable with a programmer.

Yes, the analog-side 8049 has been dumped and is available from ko4bb.

+1 to comments by pqass and Kleinstein.

Without the ASIC magic , the rest of the hp3478a is non remarkable and IMO a waste of time to try and duplicate. You also do not want to be looking at, let alone writing, 8039/8049 firmware in 2024. I speak from experience

6

General Technical Chat / Re: Is LinkedIn worth keeping?

« Last post by Halcyon on Today at 01:31:19 am »

I tried to add Dave as a connection, very long time ago. But it's only famous celebrities that are "on the list" lol. Didn't make it.

I'm not even connected to Dave! My invite ended up expiring because he never uses it.

7

Beginners / Re: 555 driver and Transformer questions

« Last post by Andy Chee on Today at 01:23:34 am »

This context is most helpful and would’ve been appreciated in your first post!

So just to confirm, you’re seeking to build a replacement HT supply for a car valve radio operating from 6V system?

In other words, you’re not attempting to use this power supply to run a different HV device like a Tesla coil, taser gun, electric fence, or other?

So extra questions, are you just trying to replace the vibrator unit? Or the entire HV power supply?

8

Manufacturing & Assembly / Re: Fellow LPKF equipment users?

« Last post by rsaxvc on Today at 01:16:16 am »

I've noticed the local harbor freight tools carries 20-pack of what appear to be compatible 38mm carbide drill bits, up to 1.1mm diameter, $7. No testing yet.

9

RF, Microwave, Ham Radio / Re: fake MPF102s from AliExpress

« Last post by radiolistener on Today at 01:09:51 am »

almost all transistors on aliexpress are fake. It can be branded but remarked other type, old repackaged, or just custom made with unknown parameters.

10

Projects, Designs, and Technical Stuff / Re: Vacuum Fluorescent Display Driver

« Last post by bostonman on Today at 01:04:10 am »

All the solder connections on the VFD looked good, however, I re-flowed them anyway including the ribbon cable.

FL1 and FL2 to ground is high impedance, 9.7ohms across the two pins FL pins, and approximately 1.3ohms across the two FL pins when the ribbon cable is connected to the unit. All other pins on the VFD to ground was (I believe) 4xx k. Not sure if these are good, but seems correct based on the FL lines being AC (most likely this is the resistance of the output transformer).

I found a previous message that states the DC/DC pins are off by one which makes sense when compared to the schematic.

Tomorrow I'll measure the SEG lines to see if they are going to approx. 38V, but what should the AC voltage be?

As for measuring the new HV518, obviously the VFD needs to be removed again, and this eliminates measuring voltages under a load since the VFD isn't connected. The other thing I'm keeping in mind is the start up sequence.