Author Topic: ESI DB655 Teardown (Read 8964 times)

Vgkid · « **on:** May 22, 2015, 06:45:35 am »

This is a teardown of my ESI DB655, aka my $30.00 decade box.
Firstly the after pics will be posted befor the befor pics.
Image(1) shows the outside of the unit. attached to the unit is a tilting axis, that allows the whole decae to be tilted up, or stay flat.

Image(2)shows the units 6 decade dials arranged so that the resistance is read byreading the numbers individually. currently reading 123.456Kohm. Note zero resistance is measured at .028 ohms, 4-wire,OC compensation,6dig,100nplc.

Image(3)shows the input terminals, on this unit you can tell that they are quite messed up, and falling apart.

Image(4)shows the internal layout of each decade portion. each decade is made up of 6 resistors. (5)2R,(1)1R.

Image(5) shows the (5) 200K .05% resistors, and (1) 100k .05% resistor. actually much better

More pics to come in the following days, questions/comments?
I just realized that this is my first teardown, comments appreciated.

Theboel · « **Reply #1 on:** May 22, 2015, 11:15:21 am »

I am sorry You mean USD30 or USD3000

You are sooooooooooooooooooooo lucky my friend
btw nice pic

Vgkid · « **Reply #2 on:** May 22, 2015, 04:29:13 pm »

The before pics:
The front:

inner dial:

outer dial:

The tilting mechanism, kind of pointless to me.

@ Thoebel I will answer your statement next post. I should have taken more pics when I got the unit :/

cncjerry · « **Reply #3 on:** May 24, 2015, 05:21:09 pm »

I have one of these and love it. After carefully cleaning one wafer switch it works perfectly and measures below .01% across the dials. I think I paid $60 for it, what deal. Mine is in great shape, it looks almost unused. I am looking for quality posts to replace the older and looser banana jacks. The jacks on your unit are very high quality but loose I assume as well.

Vgkid · « **Reply #4 on:** May 24, 2015, 08:57:51 pm »

When i got the decade all of the ranges 1k and above were good, but very noisy. When shorted the zero ohms reading was really drifty.the 1 ohm range was shorted above 4 ohms. The 10 ohm range was an intermittant short on the highest 20 ohm resistor. The 100 ohm range was working, but noisy. Taking the unit apart i found out that all of the resistors were good when tested individually(in circuit). The one ohms had shorted against the case, so i pushed them in. The one faulty 20 ohm was intermittant, but not shorted against anything. I tried to quickly desolder it to test that resistor, but couldn't. So I contemplated cutting the leads, but didn't. Upon adding more solder i found that it fixed itself, not sure how it happened(it works, there was not a broken solder joint). Upon getting the unit back together there was still alot of noise in the readings.
Cleaning time. When i was inside the unit everything felt like it was covered with tacky oil. So i removed each unit first cleaning with pure ammonia and dish detergent mixture. Followed by hot soapy water, then a bot water rense, then 90% ipa bath. During this time all the switches were rotated through about 20 times. Foowing the cleaning of the other range I put the unit back together. Everything worked well except the highest range. Since those were cylindrical resistors, i figured wster was trapped inside. Into the oven it went.
putting it back together everything worked well. Sorry for the wall of text.
Stay tuned measurements inbound.

cncjerry · « **Reply #5 on:** May 25, 2015, 07:25:45 am »

What is the 4-wire resistance of yours set to all zeros? Mine is .0262 ohms.

Vgkid · « **Reply #6 on:** May 25, 2015, 02:53:17 pm »

Generally around 00.028X ohms.

Vgkid · « **Reply #7 on:** May 25, 2015, 05:31:03 pm »

Here are the percentage error calcs done in a graph form the one 10 ohm resistor throws all of the odd 10 ohm range readings, I'm debating on if I should do something about that.

cncjerry · « **Reply #8 on:** May 25, 2015, 05:57:42 pm »

I would carefully clean the contacts for it. I used one or two passes of 2k grit sand paper but I would try just regular paper first after contact cleaner. They are tough to get to so you have to rig up something with forceps. If you have to rewind it you can get resistance wire and get really close.

Vgkid · « **Reply #9 on:** May 25, 2015, 07:42:14 pm »

@ cncjerry
What do you mean by loose banana connectors?

Vgkid · « **Reply #10 on:** May 26, 2015, 07:08:28 pm »

Mini bump. I've decided to keep the faulty resistor in for now, though i could always put it in parallel with a much larger resistor. Around 11k should work.

cncjerry · « **Reply #11 on:** May 27, 2015, 06:38:09 pm »

Loose banana connectors: On many of my old devices including the DB655 the internal diameter of the banana jack (female, panel mount) is larger in diameter than the common standard so the more modern banana plugs fit loosely. The panel mount jacks on that device are high quality so I hesitate to replace them. If I use the Probemaster spring loaded sheath type banana plugs they pop out.

I was close to ordering the Pomoma tellurium copper type as a replacement but haven't had time. I thought about making a crimping tool to compress the jacks but it is my understanding that tellurium will fracture, if indeed the DB655 uses that type originally.

Vgkid · « **Reply #12 on:** November 07, 2015, 06:33:48 pm »

I was about a 75(H2O)/25 (NH4) hot water mix with dish soap. The entire inside of the unit was just covered in a sticky film of oil. From washing dishes, ammonia is pretty good at removing oil. I can go into my cleaning process, that was not the only step.

Vgkid · « **Reply #13 on:** November 07, 2015, 08:35:59 pm »

Ammonia is a common(I love it) household cleaner.look in the cleaning section.
That 9lb seems correct. The tilting stand weighs quite a few pounds, it is solid cast iron.

Macbeth · « **Reply #14 on:** November 07, 2015, 09:08:26 pm »

Nice. I just got an esi Dekavider RV622A kelvin-varley divider. It has the same type of wirewound resistors. Last calibration sticker 1973.

I've tried all its ranges and it appears to be bang on which is just as well as there appears to be no way of adjusting it! Much better than I was expecting for $100.

I can't find a manual for it other than the RV722A version which is the new version by IET.

I'll post some pics later.

ETA: I've got the same problem with the binding posts - just a bit too wide but also not deep enough. However they are slotted to accept wires so I'm happy enough with that.

Vgkid · « **Reply #15 on:** November 08, 2015, 12:24:06 am »

I look forward to that teardown.
Try emailing IET Labs about a manual. They are pretty supporting of the old GenRad gear, just ask.

The Soulman · « **Reply #16 on:** April 25, 2017, 09:26:59 pm »

Old topic, but hey.
@Vgkid, How did you clean the wire-wound resistors on the glass/mica carriers?
I've got 11 of these double pole switches and about 80 of these resistors (gotten those parts for halve the price of your box, including shipping

).
However they are all dusty from lying in someone's attic or something.
Need to clean them up, after that its diy time.

Vgkid · « **Reply #17 on:** April 25, 2017, 11:47:55 pm »

Ohh Nice, I look forward to seeing what you build with them.
Regarding cleaning, is it dirt/dust or oil/chemicals.
For dirt, use soapy water, and a cotton pad/Q-tip. Be gentle on the higher ranges, the wire is thin. Follow with a water rinse/ Isopropyl alcohol.
If it is oily, then use anything you have at hand. For mine I used a mixture of Ammonia/ soapy water(heavy on the soap). I did this a few times, followed by the water>>alcohol.
Either way allow them time to dry.
Good luck.
---
Don't be afraid to keep asking questions, it has been some time since I worked on mine.

The Soulman · « **Reply #18 on:** April 30, 2017, 02:22:47 pm »

Warm water and washing-up liquid did the trick!

I've bought these resistors mainly to repair the 100 ohm/step range of my 1935 general radio 602-n decade box (0R1,1R,10R,100R, 1K ranges),
Somebody (not me) has smoked the first three 100R resistors and replaced them with some generic 5W 5% types.

From the bunch of resistors I've now got there are: 1R decade, 2x) 10R decade, 90R decade, 100R decade, 999R(?) decade, 1K decade and
10K decade.
The resistors on the other three switches where damaged beyond repair during transport apart from two 99,9K(?) and two 9,98K(?) resistors.
All where chucked in a single box, no bubble wrap whatsoever.

The 100R decade will be disassembled to repair the general radio.

The 10K range and a couple of the other switches will be reused for a diy decade box with 10k, 100K, 1M and 10M ranges, the latter three probably with standard 0,6W metal film resistors with trimmers.

Prior to those I will be building a sort of travelling volt and resistance standard, with 0,125R (8X1R paralled), 1R, 1R, 10R, 10R, 100R, 100R, 998R, 998R, 9,98K, 9,98K, 99,9K, 99,9K, 1M, 1M, 10M, 10M the last four also metalfilm probably.
The 0,125R uses multiple resistors so I can use that also for calibration of current sources and current range of my dmm's, nothing wild, perhaps up to 2,2A (=0,275mV=0,61W/8=0,07625W per resistor?).

Anyone has an idea what to do with a complete 10R and 90R decade?


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Author Topic: ESI DB655 Teardown (Read 8964 times)

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