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On Tue, 16 Mar 2021, 22:42 Ozan, <ozan_g@...> wrote:

I checked the DC recovery diodes in the HV supply as listed in other

thread

(all under the plastic cover and they are ok.
Any other suggestions?

Note that checking the leakage of those diodes is important, just a DVM
diode check doesn't discover problems.

It looks like the behavior of your 485 is different in different settings.
As the first issue are you debugging the intensity? Do you have too bright,
or too dim brightness, does intensity control make any difference?

HV supply voltage of 2000V is low. What is the impedance of your 1000x
probe? Looking at the schematic “CATH REG” can only adjust ~ +/-100V so
this is outside adjustment range. Should be the first thing to fix since
everything else with intensity depends on it.

Feedback loop around U1624 uses +50V at the top of R1642B as the
reference. Is +50V correct?
If you look at pins 2 and 3 of U1624 what voltage do you measure (should
be essentially the same and close to 0V).

Once you fix the HV supply if intensity is still problematic:
There are multiple posts about DC restorer issues I recommend you search
"DC restorer" "Grid Bias" for useful information.

The ones I know well are: Topic #180156: Although different equipment,
this topic has some DC restorer debug. Topic #180235 is a 485 with
intensity control issues. In particular looking at the circuitry around
intensity control pots. If you review both chains from start there is some
relevant information.

For time base issues, in the problematic 3 fastest settings how does the
"A Sweep" and "A gate" signals look? They are easily available at the back
of the scope with a BNC connection.
Ozan

On Mon, 22 Mar 2021, 05:40 Ozan, <ozan_g@...> wrote:

Removed solder and
re-soldered all components from triangle generator, checked all diodes

for

normal behavior (in circuit).

Did you already check CR245/CR248/CR250/CR246 and resistors R245, R248,
R250? The voltages you measured at two sides of the bridge are not
consistent if all the components are good. Perhaps component tester failed
to catch the intermittent behavior. Do you measure 1.116-0.6=0.516V at
cathode of CR248 in stuck state? Or do you measure a negative voltage (bad
CR248)?

Ozan

-----Original Message-----
From: [email protected] <[email protected]> On Behalf Of durechenew via groups.io
Sent: Sunday, March 21, 2021 7:45 PM
To: [email protected]
Subject: Re: [TekScopes] FG502 doesn't start at some specific settings

For Mark,
I do not say it's not possible, but I believe no capacitor will warm up in a minute. Plus, there are conditions when it starts right-away (lower/higher frequencies).
There are (usually) two other plugins (DC502 and DM501A, great instruments - after some improvements) that always start and work without problem.
There is no IC in that stage.
A transistor with leakage current - one of the ideas I have in mind and didn't verify yet (specially Q204, Q210).

For Ozan,
Are +17V, "+17V (DCPL 1)", -17V, "-17V (DCPL 1)" on sheet <1> stable when cold (not working)?
Always stable (working or not) and (well) within spec, including ripple (I did a full calibration)

In the happy non-working state what are the voltages (partial list is OK if you don't have them all):
1) at the gate of Q200, and collector of Q292. As following: 1.124V at Q200-G, 1.116V at Q292-C (might be higher at gate of Q200, as I'm introducing in the circuit the input resistance of MM - 10 mohms; MM is a Fluke 179)
2) bases of Q230A and Q230B: -0.045V both
3) bases of Q290 and Q292: -9.01V both
4) emitters of Q140 and Q175: -6.47V at Q175-Base and 6.54 at Q140-Base (I don't have measurements for E, worth checking; but why would start at higher frequencies, same devices)

In case gate circuit is acting funny: Voltage at collectors of Q325 and Q315: I didn't verify if it's acting funny, but that circuit should have no influence as long as that input is without signal; and, again, why it starts at other ranges of frequencies?

What are the test points for the different traces?
Ch1: output of plugin (scope it's AC coupled, but no difference if in DC)
Ch2: Q292-C
Ch3: Q230B-B (Q230A and Q230B are pair in the same capsule, in my plugin; seems other SN had separated ones)
Ch4: Q230A-C (AC coupled, DC level is around -9V) Thanks for comments, got something to think about and do tomorrow TT

On Sun, Mar 21, 2021 at 17:38 - <rrrr6789@...> wrote:

Steven said:

Another “plastic rot” question. I have a set of Xcelite tools. One of them,
a stubby Philips screwdriver, developed a white coating on it that was
impossible to remove without sanding it off. I could get some of it off,
but it kept re-developing this. None of the other tool handles has done
this. The handles, I believe, are a butyrate plastic that gives off butyric
acid as it oxidizes but they all are and this is the only one that
developed this white coating. The whole tool kit smells rather like vomit
(my wife refers to it as my “vomit tool case”) but this is common with
butyrate plastic-handled tools.

That butyrate plastic deteriorates into butyric acid and yes, I'm told
that that is what gives vomit it's nauseating smell. It's similar to, or
the same, compound found in milk that is going bad so human reaction to
that smell is thought to be a survival mechanism. I soak those old Xcelite
tools in full strength household ammonia and then scrub them with a brass
bristle brush or a tough nylon pot scrubber and that will remove the white
film on the tools. You may need to repeat the process a few times.
Surprisingly, even a brass bristle brush doesn't seem to harm or to scratch
up the plastic handles (YMMV!) I've cleaned several dozens of Xcelite
tools like this over the past 6 or 7 years and I've never found any sign of
damage by cleaning that way.

On Sun, Mar 21, 2021 at 2:49 PM stevenhorii <sonodocsch@...> wrote:

I think polyethylene foam instead of the black polyurethane foam does not
have the “get goopy and stick to everything” problem. Has anyone had
polyethylene foam degrade like the black stuff? I have not - either black
or white polyethylene has stood the “test of time”. I have seen foam

rubber

turn to dust, but at least it does not (in my experience) get sticky.

Apparently the polyurethane foams also outgas as they degrade and this

can

leave deposits on stuff - think camera optics as many camera carrying

cases

use polyurethane foam.

If I have some custom-fitted black foam in a transit case, I put the item
in a plastic bag and before putting it back in the case.

Another “plastic rot” question. I have a set of Xcelite tools. One of

them,

a stubby Philips screwdriver, developed a white coating on it that was
impossible to remove without sanding it off. I could get some of it off,
but it kept re-developing this. None of the other tool handles has done
this. The handles, I believe, are a butyrate plastic that gives off

butyric

acid as it oxidizes but they all are and this is the only one that
developed this white coating. The whole tool kit smells rather like vomit
(my wife refers to it as my “vomit tool case”) but this is common with
butyrate plastic-handled tools.

A comment on Duracell batteries. I am pretty sure there are counterfeits
out there - particularly the “bulk packs” with no Duracell label on the
outside. Here’s an article on fakes:

When I have had Duracell batteries (the AA ones in particular) leak, on
checking, they were the ones I bought in unlabeled bulk packs. I

generally

remove batteries from equipment I am not going to use frequently.

Steve Horii

On Sun, Mar 21, 2021 at 12:01 Harvey White <madyn@...>

wrote:

As I've mentioned previously, the latest run of Duracell (guaranteed

not

to leak before 10 years) does exactly that, and often in the package.

The good news is that they will often give you money to replace the
damaged item if you call them. Their warranty is "repair or replace",
but you do have to call.

I've had the foam in probe cases crumble, (both HP and Tek), anti

static

foam corrode and crumble, etc...

Harvey


On 3/21/2021 9:50 AM, David Slipper wrote:

Nasty!! I wonder what other time-bombs are awaiting us!?

I'll certainly be checking my stock of bits and spares.

I always assumed that a famous brand of NiMh batteries were supposed
to be leak proof - Hah! I nearly lost a pair of nice walky-talkies

and

a multimeter that way, so now cells get removed from rarely used

items

and I make a point of checking torches and the like regularly.

Sadly not surprised at anything these days,
Dave


On 21/03/2021 13:07, - wrote:

Well, this thread just showed up on EEVBlog. This is exactly the
kind of
damage that I used to see happen to IC and to TE accessories that

were

stored in the old antistatic foam.

<