Valhalla 2720GS

[Kosmic]

Make sure you are really gentle with the high voltage transformer. Mine shorted after being removed / reinstalled. It's not like I dropped it or something. I guess the cables were bent a bit too much 

anyway I still need to source a new one.

Houston we have a problem. Seems like the dying caps took the HV transformer with them. Anyone has any detailed info about that xformer?
I better check low voltage transformer too.

-branadic-

Look like I might had the same issue. In my case, the transformer failed just after I fixed the highvoltage psu where a cap shorted. The transfo survived the operation but failed shortly after.

coromonadalix is right, the transformer has 3 windings on the secondary side. 16V, 115V, and 1100V. Not sure of the VA requirement for each windings though.

I was thinking to ask a quote from https://www.heyboertransformers.com/. Let me know if you are interested, we might have a better deal if we ask for 2 units.

The other option is to rewind the transfo manually but I would definitely prefer not to.

[branadic]

I was thinking to ask a quote from https://www.heyboertransformers.com/. Let me know if you are interested, we might have a better deal if we ask for 2 units.

Any possible option is welcome. Let's see how far we can get.
In parallel I'm also trying to find out who is able to replicate the transformer here in Germany. In best case and if required to get prices down we could have made even a few more, I'm sure we are not the only guys with that issue?

Let me ask, is your unit working even without the HV power supply board and the HV transformer or does it throw out an error if both are missing?

The other option is to rewind the transfo manually but I would definitely prefer not to.

Me neither.

-branadic-

[branadic]

Attached the EEPROM (AT27C256) content of "Main Microprocessor Board" in case someone needs it in the future.

Anyone has an idea on how to read X2210 and X2212 with TL866II? In theory it should be possible, as FM16W08 and FM18W08 could be read/written using corresponding Dallas chips, but there is nothing similar for these chips. 

On the other hand these chips could be replaced with FM16W08, leaving out four of the address lines.
https://www.eevblog.com/forum/projects/x2210-and-x2212-nvram/msg4861997/#msg4861997

Any guess or suggestion?

-branadic-

[Kosmic]

Let me ask, is your unit working even without the HV power supply board and the HV transformer or does it throw out an error if both are missing?

I only tried with the HV transformer unplug and the unit start but refuse to output anything, even low voltage.

[coromonadalix]

must be the 16v   lines i think .....

[branadic]

page 6  show the connector pinout of the xformers  ... searching for the voltages

p34 p35 shows  some of them  not sure if we all of them

2x16v ac ? with an ct
2x 115v ac ?
2x 1100v ac ??

that give us 7 wires ??

Yes, 7 wires, 2x red, 2x green, 2x purple, 1x yellow. But that is only one connector, there is one more including two wires that are directly soldered to the main board and one earth wire? screwed to the base of the xformer.
Already tried contacting some companies today, but couldn't reach some person with the proper knowledge yet. I give it another try tomorrow.

-branadic-

[coromonadalix]

sorry wasn't clear enough, i think it must have some voltage detection(s) on theses line(s)

if one is dead it doesn't work

[Kosmic]

My shorted transfo has been sitting in paint thinner for quite some time now (to soften the varnish and allow disassembly), maybe it's time to start unwinding to understand how it was constructed exactly.

[TheDefpom]

Someone by accident has the CAL key? It's missing on my unit, but before I order a replacement key switch, maybe someone can help?

-branadic-

I have one. I'll check if I can make a copy.

Done! I had to go see a locksmith but that was no problems.

Excellent, my 2703 is missing its cal key and I am tired of using lock picks on it LOL... maybe that picture will help me sort out a replacement, the Datron key is similar but won't turn :-(

[maxwell3e10]

Guess where the recent 2720GS E-bay sale end up. So far it seems to work reasonably well. Passes all tests and calibrations except for the DVM, which fails checks and calibrations and gives somewhat flaky readings. The initial drift upon turn-on is not too bad.

The nice aspect of this system is very high voltage resolution, 0.002 ppm below 6V. However, the output is noisier than I would have liked. There are also periodic spikes every 10 min which I believe are related to internal comparison between the voltage references. Has anyone else seen those or is it a fault in this device?

In the long term it maybe interesting to replace LM399 with ADR1399.

[Kosmic]

Quick, check all the caps before it blows up 

[Kosmic]

The nice aspect of this system is very high voltage resolution, 0.002 ppm below 6V. However, the output is noisier than I would have liked. There are also periodic spikes every 10 min which I believe are related to internal comparison between the voltage references. Has anyone else seen those or is it a fault in this device?

I remember monitoring my unit for 24h on 10V with a 34401a and did not noticed any spikes. But, it was just a really quick test and I might had missed something. On my side self tests were passing with success.

[maxwell3e10]

I was pleased that it had a calibration sticker from 2020, so hopefully mostly kept on, which should help with the capacitor health. They look fine, but should be replaced, of course. The parts list should help with BOM.

It is supposed to check each of the references against the average every 10 min. I am not sure if that requires disconnecting each one in turn from the average, which would of course shift the mean around.

Here are a few more picture. It seems to have a battery style different from other pictures I saw.

[coromonadalix]

i would check if the hv xformer seems ok   ... non burned epoxy  enamel  etc ...   some good visual look ...

[branadic]

Congrats to your new toy. Hopefully, you can contribute with photos of all your boards and measurements on your HV transformer? That would be great for a few people.
I highly recommend to quickly replace all the electrolytics before they go bang. I received a first package full of capacitors yesterday, but haven't worked through all the boards yet to spot all needed values, so a second order is likely, before I can share my capacitor replacement list.

-branadic-

[branadic]

I've pulled the transformer and took a few photos, please find them attached. The dimensions of the EI core are 96 mm x 80 mm x 33 mm, with a single chamber.

-branadic-

[branadic]

Attached is my recapping list with links to mouser.
I also attached the ROM file from the TMS27C256 that is sitting on the front panel board.

-branadic-

[branadic]

My shorted transfo has been sitting in paint thinner for quite some time now (to soften the varnish and allow disassembly), maybe it's time to start unwinding to understand how it was constructed exactly.

Have you started your disassembly? I'm currently off without access to the device, but received a view quotations already, spreading from 500 to more than 1400€. I also asked for a ring core transformer, which should be possible, but that requires better specification of the required output power for the several output voltages.

-branadic-

[branadic]

maxwell3e10, could you help us to measure resistance and impedance of the HV transformer, (both primary windings as well as all secondary windings) as long as yours is still intact? That would help us a lot in asking manufacturers to replicate it or to wind a custom ringcore transformer.

-branadic-

[maxwell3e10]

Yes, I can measure the inductance and resistance of the windings.  But I wonder if it would be possible to just use a transformer with a 16V output and live without 100V and 1000V ranges (I would almost prefer that, less chance of things blowing up).

I think the self-test system is relatively forgiving. On mine it first says that all ranges have a fault, then it says the DVM has a fault (the DVM is a V-to-F meter of the output voltage) and after that the output works fine. So I think it just gives up on using the DVM to check the output voltage.

[maxwell3e10]

Here are the transformer measurements. One thing it note is that nomenclature is a little off, 16VAC is actually 32V CT and 115VAC  is 230V CT. The center taps for the two windings are common. The two extra wires coming from the transformer to the board are just connected to each other on the board.

[Kosmic]

My shorted transfo has been sitting in paint thinner for quite some time now (to soften the varnish and allow disassembly), maybe it's time to start unwinding to understand how it was constructed exactly.

Have you started your disassembly? I'm currently off without access to the device, but received a view quotations already, spreading from 500 to more than 1400€. I also asked for a ring core transformer, which should be possible, but that requires better specification of the required output power for the several output voltages.

-branadic-

Sorry, no update on my side. Got busy with some other stuff.

[branadic]

Attached is what I found on my transformer. What is hard to spot in the schematic page 34 due to poor quality is the common center tap for both, the 32 Vac and the 230 Vac. Looking at the connector it already indicates this scheme by how the wires are arranged.
The 1100 Vac winding is as expected shorted and shows some 0.6 Ω on my transformer.
Green/green (230 Vac with CT) winding reads 71.3 Ω (52 Ω measured by maxwell3e10), violet/violet (32 Vac with CT) reads 6.9 Ω (8 Ω measured by maxwell3e10) or if you want to put it in a different way: green/violet/yellow/violet/green = 31.7 Ω/35 Ω/38.3 Ω/71.3 Ω

maxwell3e10, could you please measure resistance on the low power transformer too? I'd like to have a sanity check to be sure it is not defect.

-branadic-

[branadic]

Maybe the mods are gentle enough to move that thread into the metrology section? It's better located over there.

-branadic-

[branadic]

After recapping the unit, replacing the carbon composite resistors inside the oven and socketing the X2212 on the reference boards I took some quick pictures.

-branadic-