Alternative to Faceplate/Preamp unit for Table Radios...

[tomzarbo]

No pin hole that I see. Also, wiggling side to side while pulling doesn't seem to do anything, I'm already pulling a lot harder than it seems I should. No need to go further, I have a connector and more ribbon cable coming anyway.

TomZ

[Millstonemike]

It doesn't look to have a mechanical way to release the ribbon from the board, and I pulled on it as hard as I dared... so I think that one might be permanent.

TomZ

Actually, I think the cable slides out without a release. It's just very snug via the contacts. Wiggle side-to-side when pulling up. That is:alternating pulling more on "pin 1" than pin 20 and vice-versa.

Could there be a pin hole to activate the release?

https://www.youtube.com/watch?v=wewE6DbKhac

[Wolf]

You're dealing with 'headers', so searching for that might help you.
PS- AllElectronics stocks some of this stuff, and is stateside....
Later,
Wolf

[tomzarbo]

I took some pics of the cable where it attaches just for fun...

Front board attachment:


It doesn't look to have a mechanical way to release the ribbon from the board, and I pulled on it as hard as I dared... so I think that one might be permanent.

Rear board attachment:



The little bottom black plastic piece pushes in and wedges the cable in once it's positioned. It has a real firm grip when locked in.
Amazing they get the holding power they do with these tiny little fittings!

Hope to mess with this on Sunday, church is cancelled due to the virus, so I'll have a little more time home.

TomZ

[tomzarbo]

Maybe this will shed some light ...

https://www.youtube.com/watch?v=PimDML9YHoY

That's interesting. Thanks for finding that. I've messed with a few of these video board thingy's and have had to remove the ribbon cable a few times. A few of the other video players used the push in and tilt down method. This car radio uses the style where you push in the ribbon... no resistance at all... then you push in a plastic piece underneath which (I think) wedges the whole shebang closed tight.

I took some pics of the ribbon connected to the front board and I don't see any clips, buttons, or anything or any way to remove it. This one must be a permanent, solder-in type of connection. I took some pics, but I'll have to post them when I get home.

Hopefully I can get some time this weekend to tinker with this. I suspect in a few weeks, I'll be getting a break weather I want it or not if this Corona virus keeps up. :(

TomZ

[Millstonemike]

Maybe this will shed some light ...

https://www.youtube.com/watch?v=PimDML9YHoY

[tomzarbo]

Not sure, but I believe the connector on the amp board is made to be opened to replace a cable. But an extension is foolproof so for a buck or two more, that's likely the best way to go.

Even with the longer cable I'd be looking at removing what ever I can from the amp board - the power out speaker connectors and the RCA line out connectors are "low hanging fruit" (you can solder the L-R signal wire into the original holes). That's got to remove a lot of bulk from the amp board. After that, the power amp itself. And without using the amp, that 35 V 2200 uf cap could be replaced, perhaps with a much smaller value. How much "surgery" depends of the arrangement of the target system.

I was able to remove the cable from the rear board by sliding out the plastic 'shim' and just pulling it out. Where the ribbon connects to the front board, however, I don't see a way to 'release' the cable, unless I'm missing something.

I just purchased some 8" cables, some connectors to join the two ribbons, and a few of the 12 delay relay boards.
I purchased from Aliexpress, so it's probably going to be mid-April before I get them.

So do you think the amp chip could just have the leads clipped to remove the space it takes up, and things would still function properly then?

If the RCA outputs, two plug-in cable connectors for power/speaker output etc, and the antenna jack were removed along with the amp, that's a pretty tiny little board that could be shoved in a small sliver of space. Maybe if noise or interference isn't an issue, it may even be able to be mounted with a few plastic bits to the front panel via the four plastic 'ears' that connect the black face to the metal frame.

TomZ

[Millstonemike]

Now that I've looked at it... the cable does have 20 pins, and is exactly 2 centimeters, 1 millimeter wide.
So I think that's a 20 pin, 1.00 mm pitch cable, just like you referenced above. It would be 'forward direction, oriented since I want the exposed metal side on the same side as it already is.

I found it on Aliexpress for 10 of them for a few dollars. I'm going to get some extension boards as well to connect the existing ribbon to the new ribbon, since it doesn't seem to disconnect from the front board.

TomZ

Not sure, but I believe the connector on the amp board is made to be opened to replace a cable. But an extension is foolproof so for a buck or two more, that's likely the best way to go.

Even with the longer cable I'd be looking at removing what ever I can from the amp board - the power out speaker connectors and the RCA line out connectors are "low hanging fruit" (you can solder the L-R signal wire into the original holes). That's got to remove a lot of bulk from the amp board. After that, the power amp itself. And without using the amp, that 35 V 2200 uf cap could be replaced, perhaps with a much smaller value. How much "surgery" depends of the arrangement of the target system.

[tomzarbo]

Now that I've looked at it... the cable does have 20 pins, and is exactly 2 centimeters, 1 millimeter wide.
So I think that's a 20 pin, 1.00 mm pitch cable, just like you referenced above. It would be 'forward direction, oriented since I want the exposed metal side on the same side as it already is.

I found it on Aliexpress for 10 of them for a few dollars. I'm going to get some extension boards as well to connect the existing ribbon to the new ribbon, since it doesn't seem to disconnect from the front board.

TomZ

[Millstonemike]

[QUOTE=neildavis;n1433931... but the pull-up resistor on C34 is probably connected to 12V (Vs), not 5V, It doesn't really make a difference, but in case you are buzzing out the circuit, it might help to know that. And as Mike said, experimenting with a larger value of C34 will slow down the rise time and possibly make that power-on pop less annoying.[/QUOTE]

That may explain another issue I see. The pull-up resistors near C34 are 100K ohms. The datasheet lists input impedance at 100K ohms (the datasheet does not specify whether that impedance is for signal inputs, control inputs or both). If the control input impedance is circa 100K, feeding the 100K pull up resistor with 5 V would not be able to bring the input up to 3.5V to turn on the amp.

[neildavis]

I'm guessing that amp chip is from UTC. UTC is a major semiconductor house and they have a lot of parts that are unique to them, but they also sell "old gold" parts that were originally developed by other vendors such as ST and National. The block diagram in their datasheet for the TDA7388 shows some more details of the "standby" function. As you can see, it does what you wanted: it removes power from the amps:

The standby voltage is compatible with CMOS voltage levels (1.5V/3.5V), but the pull-up resistor on C34 is probably connected to 12V (Vs), not 5V, It doesn't really make a difference, but in case you are buzzing out the circuit, it might help to know that. And as Mike said, experimenting with a larger value of C34 will slow down the rise time and possibly make that power-on pop less annoying.

[tomzarbo]

So I was able to do a little messing with this.

There was continuity between Pin #4 (standby) on the amp chip and the right side of C34.

There was also continuity between the left side of C34 and ground (I used the black line on the 12v input on the back of the unit for this)
It looks like you were right Mike.

Now I have to carefully shunt the cap while the amp is powered up and playing... the amp should go silent as it will be in 'standby mode.' I'll check the amp draw while I'm doing this if I can to see what the drop is.

Regarding the ribbon cable, you were right, 20 lines, really hard to count something that small. It does disconnect from the rear board, but looks to be solidly attached to the front board and is not removable.

Thanks again for the help, I'm kind of enjoying messing with this.

TomZ

[Millstonemike]

Yes, cut power and the relay goes back to it's default position. Note energizing the relay will add some 40 ma draw on the power source.

I noticed in another pic that the resistors near the C34 are 100K ohm. That would extend the turn on delay 10 times over the mfg's design. Somewhere in the neighborhood of 120 ms. Of course, there's no way to tell the value of the cap short of measuring it.

[tomzarbo]

Mike,
you mentioned this Time Delay Relay before in my Toni Table Radio thread and elsewhere....



The 12v version is cheap enough, but one thing I can't seem to find out is: does it turn off immediately after power is cut. I assume it does and that it's too obvious to mention, but I just wanted to check before I order up a few along with some ribbon cable.

I'm going to see if I can mess with the cap tonight if I can get my eyes uncrossed from Tuesdays workday goings-on.

TomZ

[Millstonemike]

You got it. That's my guess - C34. If C34 isn't it, you can find the cap by testing for continuity to pin 4 with nearby SMD caps. The large 47 uf Can cap is Vcc+ bypass/filter cap.