tandon tm7516 dead?

[Elvi]

i have this tandon tm7516 that i think is dead but a nice museum piece nonetheless, push power button and the psu turns on but that's basicly it no beeps or screen info except the hd turns on but i guess that's just cause it gets power.

every cable i can think off has been reseated same with cards also tested another graphics card and also had this pc's card in another pc to test it, ok.

some simple info i've found on this thing can be found here http://electricdreams.ath.cx/comp/ttm7516.php?current=2&s1=1 boy does this pc have alot of plating and screws :roll:
it was like this when i got it home, when i tested it at the old owner it worked funny enough, this was a few years ago btw, this is 1 of the first other pc's in my collection.

 

[Agent Orange]

Elvi:

If you have a VOM you may want to check your PS voltages. Be sure to check the system battery.

 

[Elvi]

i guess this is in the wrong section and i do have a volt meter but i'm not very used to these old psu's it's not a at supply, different plugs and i kinda doubt a bd bios battery would not let the system atleast show some signs of life or?

 

[Elvi]

it would be nice to have some other insights or suggestions to this old thing, havn't managed to actually get around to it yet thanks to my voes with the kaypro2 but that's another story

 

[Elvi]

uploaded these images if it would help solve this in any way.

the psu mobo connector, not standard AT configuration so it's hard to know what is what except the black wires.


image of the top part of the mobo where the cpu and the power connector is and battery.

when i tried to meter the voltages of the molex i got ca 11.3v on the 12v side and 5v on the 5v side, also the psu "ticked" a litle before it turned on when it didn't have anything attached to it.

 

[Agent Orange]

uploaded these images if it would help solve this in any way.
View attachment 7576
the psu mobo connector, not standard AT configuration so it's hard to know what is what except the black wires.

View attachment 7577
image of the top part of the mobo where the cpu and the power connector is and battery.

when i tried to meter the voltages of the molex i got ca 11.3v on the 12v side and 5v on the 5v side, also the psu "ticked" a litle before it turned on when it didn't have anything attached to it.

That a start. While you're at it, check lithium cell for 3 volts - best to do when unplugged.

 

[modem7]

also the psu "ticked" a litle before it turned on when it didn't have anything attached to it.

Most switch mode power supplies need to be loaded by at least a certain amount. The ticking suggests that your power supply needs to be loaded. Do the measurements when the power supply is connected to the motherboard.

the psu mobo connector, not standard AT configuration so it's hard to know what is what except the black wires.

Because of the large quantity of red wires, red will be +5V.
What does the orangle wire measure?
What does the blue wire measure?
What does the white wire measure?

and i kinda doubt a bd bios battery would not let the system atleast show some signs of life or?

If there is no isolation diode on the motherboard, and the battery is low, it could cause a problem. It is unlikely that there is no isolation diode, but it is possible. I have an old Trio oscilloscope that has no isolation diode, and when the backup battery for the push-button settings goes low, the oscilloscope won't start.
As Agent Orange wrote, you need to measure the battery.


Have you tried disconnecting the hard drive completely (both data cable and power cable)?

Have you tried disconnecting the floppy drive completely (both data cable and power cable)?

 

[Elvi]

the psu doesn't have to be connected to the mobo to turn on, i guess it just ticked cause it's not been on for a long time, now every time i turn on the switch it's almost turns on immediately.

red and white gives 5v
orange 12~v
blue -12v

the battery gives no charge at all, seems to be 3.6v that it should hold.

all drives disconnected when testing aka all cables.

btw all the keyboard leds turn on when the pc is turned on but never turns off.

 

[Compgeke]

Lights staying on is an interesting thing as I've seen computers that don't post period yet the keyboard lights go on then off, with the exception of the AT&T PC-6300 which does some trippy stuff with the LEDs when booting (flashing).

As I've never worked on one of these I don't know if that is a hard coded error, but I would check the keyboard controller as the LEDs stay on, an unusual thing.

 

[Elvi]

and how would i check the keyboard controller then if the pc doesn't even boot?

 

[Compgeke]

If it's a standard one, swap it out, far easier if it's socketed. However, if there is no video that's also another problem. One of the easiest things to do would be to find an ISA Post Code Reader to see if it's even trying to boot.

 

[Elvi]

harldy any chips are socketed on that mobo and i havn't even seen anything that resembles a chip like that.

 

[modem7]

red and white gives 5v
orange 12~v
blue -12v

The white wire is probably a POWER GOOD signal, but may not be (e.g. could be a +5V sense line). Nonetheless, the fact that the wire is sitting at +5V is a good sign.

Were those measurements done with the motherboard connected? If not, try again with the motherboard connected - if one or more voltages disappear, then that means that something is shorting out the power supply.

the battery gives no charge at all, seems to be 3.6v that it should hold.

Right there is a problem. If the battery has gone dead, it may be the cause of the problem.
It certainly ties in with the fact that the machine worked a few years ago.

An experiment would be to try powering up the computer with the battery out.

all drives disconnected when testing aka all cables.

So from that, you now know that the hard drive and floppy drive are not the cause.
Have you tried powering up the computer with the keyboard disconnected?

 

[modem7]

as I've seen computers that don't post period yet the keyboard lights go on then off,

Quite often, that three-LED flash on power on is only the result of the keyboard receiving +5V, the flashing done by the self test code in the keyboard. For a particular keyboard, if one has suitable equipment/knowledge, that can be confirmed by disconnecting the keyboard from the computer and then applying +5V to the appropriate two pins on the keyboard plug. I've done that on many AT class keyboards, and in every case, found that it was the keyboard that did the flashing.

Of course, that doesn't mean that all AT class keyboards do that.

Lights staying on is an interesting thing

Yes, it is. If the keyboard is of the type I refered to in the previous paragraph (keyboard flashes LEDS on receipt of +5V), then a significantly low +5V may be the cause of that symptom. Elvi measured the +5V earlier, but maybe he did that with the power supply disconnected from the motherboard.

 

[Elvi]

doesn't look like it's possible to mesure the psu while it's attached to the mobo, battery/keyboard unplugged, no change.

 

[Elvi]

nevermind i got a white cap off the plug and then i was able to messure it WITH the psu plug connected to the mobo, all seem to be at their right place, funny tho that the orange +12v shoved 12.3v now, when the plug was loose it showed 11.3v

 

[modem7]

nevermind i got a white cap off the plug and then i was able to messure it WITH the psu plug connected to the mobo, all seem to be at their right place,

So nothing overloading the power supply.

To me, everything so far suggests a faulty motherboard. There is still the possibility though, although I think it unlikely, that the design of the motherboard is such that it might require a good battery.

+5V good. Odd then that the keyboard is getting +5V and the three LEDs are on solid. How does that keyboard behave when connected to a different AT clone. Do the LEDs flash on?

funny tho that the orange +12v shoved 12.3v now, when the plug was loose it showed 11.3v

If that is repeatable, then it probably the result of the power supply design (e.g. the +12V line needs a load of some sort).

 

[Elvi]

tried another keyboard on the tandon and it did the same a keytronic ps/2 via a ps/2 to din converter so that keyboard is from say middle of the 90's or therearound, all leds fully on.

i also don't know if the current tandon keyboard i'm using is the orginal for the tandon as i have a few of them, some have a xt to at switch on the back and some don't, currently using one with the switch.

 

[Elvi]

So as the battery didn't give anything i thought i'd try a normal cr2032 3v bios battery and see if the pc would boot but nope same thing.

used a 2 pin block to attach it to the mobo pinns and tape on the round battery heh, did see that when the pc was off the battery gave about 2.99v when the pc was on i saw 3.01v on the same pinns when the battery was connected.
mesured the pinns on the mobo with the battery gone and i saw a steady 4.86v.

i'm suspecting that something has happend to the mobo and it's proberly dead like i've had a feeling it was from the very begining when i got it home, i'm happy still cause i didn't pay a thing for it when i got it but still curious if i would be able to ressurect it, maybe someone else still has any ideas, just blurt it out lol.

 

[Elvi]

btw, a litle off topic but conserning tandon anyway, does anyone know the bios settings for the tandon tm262 drive? not been able to boot it on another 386 based computer with a mfm card.