Vgkid's HP 6114 repair thread

[Vgkid]

So it came yesterday. Externally it is a beautiful machine, but internally everything is not so good.(no fire this time...)
post to come.

[PedroDaGr8]

So it came yesterday. Externally it is a beautiful machine, but internally everything is not so good.(no fire this time...)
post to come.

Can't wait to see this. I want another 6114A but can't swing the new prices. Thanks to these being included in the newest Art of Electronics, prices went up to the $150+ range on eBay.

[Vgkid]

This should tide you guys over until tomm night.
I accidently smoked it somehow(A1R22,5K). The 47.5K is ok

This is not good, +/- 3v rails.

[Vgkid]

Since the adjust trimpot is fried, lets determine what value a replacement will need to be.I may replace it with a series resistor+trimpot.
So we will hook a decade resistor up to the output(starting at 47.5K) and increasing it until the reading matches the output. 40v F.S

Now lets see what value we end up with.

so the final resistance is 50.6K ohm.
So a 2.1K series resistance will need to be added.
Next ...
I went and removed the main board(A1) from the unit. It was a big p.i.t.a for a power supply, I would say that it is the worst part about of these units. I will say that just desoldering the AC inputs from the transformer , and the wires going to the Heatsinked output module makes this easier.
Good news(or bad news) all of the larger electrolytic caps are good((2)-4000uF,(4)-490uF).

[Vgkid]

wiener pics

Haha
I haven't even masturbated today.

[Vgkid]

So after figuring out what value the trimmer needed to be et to suddenly it starts to work, the display that is.
Now to start going into the depths of the machine. Checked all of the voltage on the the A2 control board, they seem to be ok.
Lets go the the A1 board shall we.
***Pics+ descriptors up soon***

[Vgkid]

Lets start the trouble shooting. Above 5.2V the output voltage is good., below that it hovers around 4.7v.
Already checked the voltage present on the A2 control board, they seem good.
Lets get to the A1 board. Starting here, is the section containing the voltage reglator diodes(zeners of the 4.3, and 2.3v variety),

Measuring VR5, it appears to be in spec.

measuring across VR4 we have 2.75v as opposed to 2.32v

measuring across VR3 we should have 4.3v instead we have 4.0v, a bit low

measuring across vr2 we have .68v, as opposed to 4.3v, a big problem here.

[Vgkid]

*** Let Me Know if Pics Do Not Load***
Resuming troubleshooting, lets test those zener diodes.
4.3V zener, this guy was a bit low, so I swapped him with the 4.14v zener on the current limit. In theory just barely in spec.

The 2.32V zener, still in spec.

My simple 4-wire wire zener voltage measurement setup. No component desoldering needed, ok only 1 zener was desoldered.

Consists of:
PSU set to 8v, in series to decade resistance box(using datasheet to find Izener, to set resistance). Then using 24awg wire wrapped around the DMM probes to make a 4 wire measurement.

[Vgkid]

Went through checking voltages/shorts/opens of everything(it seems), no difference. Swapped out A2U2 because it was kind of warm, with a op177, no change. powered it on today, output stuck at 70v. Shorted A1Q1 E>B and got 0v(good). now to go through the A2 board.

[Vgkid]

Replaced the other opamp A2U3, and checked cr2/3(both good) same issue as before, above 7v is good. Can actually dial it down to 5.00v before voltages start acting up.