JUNK STEREO REPAIR UPDATE
...So since it DID work once... it means there is nothing fundamentally broken in this stereo. CPU is fine at the least, which is the main relief. So must be an intermittent contact somewhere. Tried applying pressure with a pencil (plastic sharpie, non conductive )on the USB connector and surrounding discrete components, the CPU even... no luck, it won't come back to life.
But I guess it's got to be a dodgy joint somewhere. Logic would dictate the USB connector of course, since it takes all the mechanical stress every time she puts the stick in and out. At first glance I can't see any broken joints on its the 4 connector pins but well, I will look closer, and reflow those pins anyway, of course. Wish me luck....
Oh OK ! So you replaced the transformer ! You didn't talk about that
So OK, new transformer so you new what the specs for its windings were, and that it could supply the current comfortably.
I understand now !
I was limiting the list intentionally at 3-terminal ones. Otherwise I would have not only included the L200, but also the LM104, LM106, LM2991, LR8K4, SG1501, SG1532, ....
LM150/250/350 is a 3A adjustable between the 117 and the 138.
That's an interesting one!
I've attached the datasheet of it. Is there a similar one of the SG1501A from Linear Technology?
DOPAMIIIINNNNNEEEEEE!
I now have a fully working TDS794D!
I tracked down two bad acquisition RAM chips, U405 and U413 on channel 2. Replaced them with parts pulled from a scrap board (a smashed unit with a physically damaged acquisition board, well and truly for pulling parts..)
Now it passes all self-tests and no spurious spikes on the display. Yaaaaaaaaayyyyyy!
Next step, find probes at a not-insane price.....
Oh no...... oh help me..... it's JUNK CONSUMER ELECTRONICS REPAIR TIME again !!!
She said that the problem is that when she puts a USB stick with MP3 files on it, it doesn't work anymore. Just nothing happens, as if she hadn't inserted the stick. I confirm that.
There is also an SD card reader with the same purpose... so I put some MP3 files on an SD card and... same result, nothing happens.
JUNK STEREO REPAIR UPDATE
...So since it DID work once... it means there is nothing fundamentally broken in this stereo. CPU is fine at the least, which is the main relief. So must be an intermittent contact somewhere. Tried applying pressure with a pencil (plastic sharpie, non conductive )on the USB connector and surrounding discrete components, the CPU even... no luck, it won't come back to life.
But I guess it's got to be a dodgy joint somewhere. Logic would dictate the USB connector of course, since it takes all the mechanical stress every time she puts the stick in and out. At first glance I can't see any broken joints on its the 4 connector pins but well, I will look closer, and reflow those pins anyway, of course. Wish me luck....You can't rule out the CPU yet, buddy. It's not obvious if the USB and the SD card use the same I/O pins; all you know for sure is that when the thing tries to access the SD card, all or part of the thing (I'm thinking USB controller, which usually has at least 2 USB ports) locks up.
This exact behavior is a very common failure mode in cheap digital picture frames; I suspect similar here. Time to scope out the SD slot itself:
mnem
*tzzzzzzt*
JUNK STEREO REPAIR UPDATE
Wish me luck....
JUNK STEREO REPAIR UPDATE
...So since it DID work once... it means there is nothing fundamentally broken in this stereo. CPU is fine at the least, which is the main relief. So must be an intermittent contact somewhere. Tried applying pressure with a pencil (plastic sharpie, non conductive )on the USB connector and surrounding discrete components, the CPU even... no luck, it won't come back to life.
But I guess it's got to be a dodgy joint somewhere. Logic would dictate the USB connector of course, since it takes all the mechanical stress every time she puts the stick in and out. At first glance I can't see any broken joints on its the 4 connector pins but well, I will look closer, and reflow those pins anyway, of course. Wish me luck....You can't rule out the CPU yet, buddy. It's not obvious if the USB and the SD card use the same I/O pins; all you know for sure is that when the thing tries to access the SD card, all or part of the thing (I'm thinking USB controller, which usually has at least 2 USB ports) locks up.
This exact behavior is a very common failure mode in cheap digital picture frames; I suspect similar here. Time to scope out the SD slot itself:
mnem
*tzzzzzzt*
Who knew, who should have known.
At least, it looks quite similar to mine. But wasn't able to recognize because of the different case.
JUNK STEREO REPAIR UPDATE
...So since it DID work once... it means there is nothing fundamentally broken in this stereo. CPU is fine at the least, which is the main relief. So must be an intermittent contact somewhere. Tried applying pressure with a pencil (plastic sharpie, non conductive )on the USB connector and surrounding discrete components, the CPU even... no luck, it won't come back to life.
But I guess it's got to be a dodgy joint somewhere. Logic would dictate the USB connector of course, since it takes all the mechanical stress every time she puts the stick in and out. At first glance I can't see any broken joints on its the 4 connector pins but well, I will look closer, and reflow those pins anyway, of course. Wish me luck....You can't rule out the CPU yet, buddy. It's not obvious if the USB and the SD card use the same I/O pins; all you know for sure is that when the thing tries to access the SD card, all or part of the thing (I'm thinking USB controller, which usually has at least 2 USB ports) locks up.
This exact behavior is a very common failure mode in cheap digital picture frames; I suspect similar here. Time to scope out the SD slot itself:
mnem
*tzzzzzzt*Yeah but.......
The orientation of the MicroSD card holder suggests it's for uploading SW/FW/OS into the radio and not for use by the operator/user.
That digimess stuff is Chinese rebrand garbage. Not even decent Chinese garbage but rock bottom stuff
Some of it might be, idk I've not had any in my hands. This however, does not look like Chinese made, it looks low volume, low R&D budget, low design budget, mid-quality euro-tryhard. In fact, it reminds me of early TTi stuff. https://www.ebay.co.uk/itm/234578724312
It's from rchaudio so it's overpriced. Just to prove the Grundig lineage: https://www.farnell.com/datasheets/104629.pdf
I'd pay £50 shipped.
Seriously? £80?
https://www.ebay.co.uk/itm/384932494888
Seriously, a wet dream on his part. Bids should have started at $40 USD at most.
And then you have to modify the unregulated +5V supply for better stability. Once that's done it is a damn good DMM.
It's a terrible DMM full stop. Apart from the 5V problem it has mains routed badly on the main board, the display design and assembly stinks, the rest of the power supply stinks and the front end protection stinks.
So, when are you buying it?
Had one. Hated it.
Quite happy with the 3465A. It’s 4.5 digits as well
Seriously? £80?
https://www.ebay.co.uk/itm/384932494888
Seriously, a wet dream on his part. Bids should have started at $40 USD at most.
And then you have to modify the unregulated +5V supply for better stability. Once that's done it is a damn good DMM.
It's a terrible DMM full stop. Apart from the 5V problem it has mains routed badly on the main board, the display design and assembly stinks, the rest of the power supply stinks and the front end protection stinks.
So, when are you buying it?
Had one. Hated it.
Quite happy with the 3465A. It’s 4.5 digits as wellYeah, but the 3466A is way better, though the 3465A looks to be almost a 3466A without the annunciators.
To risk or not to risk:
https://www.ebay-kleinanzeigen.de/s-anzeige/tektronix-577-d2-defekt-/2123531071-168-3793
The USB power will not be wired to the rail directly. There will be a host controller in the IC that handles all that faff including power negotiation.
3.3v is interesting through. It should be 5V. Check it with a scope to make sure it is actually that and not the average voltage you are reading.