ITS1099 Intersil NPN Transistor datasheet ? - Page 1
Forum section: electronics / beginners

author: RichardM
author_rank: Frequent Contributor
timestamp: April 09, 2022, 03:46:31 am
content: Hi AllI normally have no problem finding datasheets but this transistor from a Fluke 8502a multimeter has me stumped. Does anyone know where to find this datasheet ?It is a dual transistor in a TO99 ? metal can.Cheers

author: ledtester
author_rank: Super Contributor
timestamp: April 09, 2022, 04:28:51 am
content: The part number might be just "IT 1099".A search of the Fluke 8502A service manual reveals a reference to a "IT 1099" transistor (page "7A-6", physical page 161 inhttp://bee.mif.pg.gda.pl/ciasteczkowypotwor/Fluke/8502A_OSM.pdf):There's another reference to that part in the 8800A user manual and it's described as a dual NPN (page 48 inhttps://archive.org/details/FLUKE_8800a/page/n47/mode/2up):

author: RichardM
author_rank: Frequent Contributor
timestamp: April 09, 2022, 04:56:31 am
content: Ok, thanks I will try to search for an IT1099.Interestingly my 8502a service manual definitely shows it a small an ITS1099

author: RichardM
author_rank: Frequent Contributor
timestamp: April 09, 2022, 05:01:17 am
content: Still not finding anything with google. Perhaps a special Fluke part ?

author: amyk
author_rank: Super Contributor
timestamp: April 09, 2022, 05:48:26 am
content: Does 2N5793/2N5794 seem like a match?

author: RichardM
author_rank: Frequent Contributor
timestamp: April 09, 2022, 06:26:02 am
content: Thanks, I guess they could be a substitute ?Do you have a datasheet for the IT1099 ? How can a replacement be selected otherwise ?

author: Kleinstein
author_rank: Super Contributor
timestamp: April 09, 2022, 09:41:36 am
content: To find a suitebale substitute the circuit the transistor is used is more important than the datasheet of the old one.In the Fluke meter this seems to be the input amplifier pair, running at a pretty low current.So one would like a transistor with good gain at very low current and low LF noise.The choice of available THT dual transistors is rather limited anyway. So chances are the strategy would be look for what can be obtained and from there check which of those few may work.If you don't mind the price point, something like MAT01 should work well.A matched pair of BC550C glued (or hold by heat shrink) would the cheap version.

author: Terry Bites
author_rank: Super Contributor
timestamp: April 09, 2022, 10:12:10 am
content: Well heres morehttps://www.parttarget.com/5961-00-361-8681_5961003618681_ITS1099.html/-A5D7A1DF-2AA5-4296-AD25-64624F67B51Fand line 26:https://analytics.supplyframe.com/trackingservlet/track/?r=0x34EY99PS_gIu2qWuzU9-Tyq0STFNRf76qStWuXLeGWD131yU9zXAENQZRSzjF74Ys7qrXSshhBDM3GFH_JPPRmGeRJWC_-kSGTcOCF_SW5oxNx6JPBkc4phA8xH7NLQ1JVmVTLG9yiLHrtL_SSrpRYCAuN7Jq7o1fDwyPiemn38uQEUT2Dz07h0INpa7-QtSWRSPTZiO0pNxBNO4hMc9zTcrQGVrsct5PlSPXxa4Kbjan7oVxk_g3RsJckxdZh1g8KiquHwgO8gFUFp-i0AIy9He4GFA2-FvO8jPXnqM0

author: Ian.M
author_rank: Super Contributor
timestamp: April 09, 2022, 11:47:17 am
content: Looking at the schematic, ('Active Filter' board) and circuit description, it doesn't see any high voltages, in spite of the +/-60V supplies to the current sources feeding it. TP2, the top end of its collector pullups is bootstrapped to 5V above the OPAMP output, and its in the OPAMP feedback loop. It operates at approx. 8uA tail current.It may be worth looking at SMD matched pairs in stock at your favorite supplier, and trolling through their datasheets for ones with decent hFE@10uA, then 'dead bugging' it.

author: Gerhard_dk4xp
author_rank: Frequent Contributor
timestamp: April 09, 2022, 02:54:02 pm
content: Some other Intersil transistor/arrays ended up in the Renesas portfolio.HFA****regards, Gerhard

author: floobydust
author_rank: Super Contributor
timestamp: April 09, 2022, 07:42:15 pm
content: What I could dig up:Fluke 585109 Dual super-beta NPN transistor, used in Fluke 8502A, 8505A, replaces Fluke p/n 284075 which was originally a Micro Power Systems Inc. MP-301-52. No data on that could I find either.I suspect it is a selected Intersil IT100 family part, there are no p/n's like it (1099) in Intersil's old lineup.Linear Systems(Digi-Keythru Marketplace) sells the parts, or the originals are for sale on the Internet.I would guess it's either:IT120A hFE 200 at 10uA, 3μV/°C lowest VBE differental wrt temperature.IT124 hFE 1,500 at 10uA, 5μV/°C more likely ?Q18 DC Signal Conditioner MIS-1100 (can't find the full sch)Q27 Active Filter PCB MIS-1130 around 4uA each (my math) and >1MEG collector resistors are quite big, really low current. R15/R16 are factory selected resistors (active filter board) so they must be additional secret sauce. It has an offset trimpot so matching can be covered a little?The service manual states "if replaced, it's necessary to send the module back to the factory for temperature compensation calibration" so the part affects temperature drift of the instrument somehow.

author: Ian.M
author_rank: Super Contributor
timestamp: April 09, 2022, 08:01:30 pm
content: Check the circuit description in the 8502A service manual - its mentioned in section 3-64 as "A dual,super-betatransistor in a differential configuration (Q27) drives U5." which IMHO backs up your guess of "IT124 hFE 1,500 at 10uA" as far more likely than "IT120A hFE 200 at 10uA".R15 or R16 are select on test (other one shorted out) to bring the offset within the adjustment range of R14. The procedure is documented on page 4-21.

author: floobydust
author_rank: Super Contributor
timestamp: April 09, 2022, 09:02:10 pm
content: I wasn't sure what "super-beta" looked like in the 1970's what numbers qualified for that term. Some Linear Systems parts claim to be "improved" but not sure where.1979 Intersil Data Book has some pretty good parts IT124B is hFE 4,000 and the IT124 came out 1970.

author: RichardM
author_rank: Frequent Contributor
timestamp: April 09, 2022, 11:18:18 pm
content: The issue I have is that the 8502a Ohms reading is either showing error 6 in auto mode or wildly fluctuating mega ohms in manual mode, regardless of the resistor under test. I have 2 8502a’s so I can confirm the ohms module itself is working fine. Definitely the active filter.I pulled the dual transistor IT1099 and it looks fine on the curve tracer to a novices eyes. I also replaced U5 and it made no difference. All the voltage rails are fine and the unit works fine for DC voltage and Current.A simple comparison of voltages between a working active filter and the problem one indicates all the voltage signal shapes (on the scope) around U5 and TP2 and TP3 look the same but the magnitude is about a factor of 10 out..I would like to undertake the calibration to select new values of R15 and R16 but the only thing I don’t understand is how to short RT2 and RT6 at the bus interconnect monitor which I do not have. How do I do this ?Getting off topic now sorry.Thankyou all

author: RichardM
author_rank: Frequent Contributor
timestamp: April 10, 2022, 03:38:55 am
content: In case I still have someones interestthis is the results of my probing of a good 8502a Filer Module v the problematic one. Green indicates the same between the two modules, red indicates a significant difference.Its looking like Q18, Q32 or Q25 is suspect at this stage ?

author: magic
author_rank: Super Contributor
timestamp: April 10, 2022, 06:45:35 am
content: And what those secret voltages are?editI suppose most of the red voltages are about equal to U5 output, so what is U5 output?What about Q27 bases?Q26,Q30 collectors?

author: RichardM
author_rank: Frequent Contributor
timestamp: April 10, 2022, 10:57:59 am
content: Quote from: magic on April 10, 2022, 06:45:35 amApprox scope readings belowQ26 collector on good module is a square pulse +5V to +20VQ26 collector on bad module is a square pulse +4V to +5VQ30 collector on good module is a square pulse -0.6V to +19VQ30 collector on bad module is a square pulse +-0.8V to +-0.5VQ27 base tied to Q25 on good module is a square pulse 0V to +19VQ27 base tied to Q28/Q29 on badmodule is a square pulse 0V to +0.3VRegardsRichard

author: magic
author_rank: Super Contributor
timestamp: April 10, 2022, 11:40:48 am
content: Quote from: RichardM on April 10, 2022, 10:57:59 amQ30 collector is Q27 emitter, it should always be 0.6V below the bases. The above seems about right, but it's the good board of course.Quote from: RichardM on April 10, 2022, 10:57:59 amGood module again. Q26 collector should always be 5V above U5 output and U5 output should follow the input from Q22/Q24/Q25 to Q27 so this result is a little weird (should be: 24V peak). Maybe some loading effect due to probes or maybe the opamp clips at ±15V output. By the way, do you know the real part number of this chip? LMI436/LM1436 doesn't look familiar.Quote from: RichardM on April 10, 2022, 10:57:59 amNow that looks like U5 output on the bad board is -1V to 0V, what's the corresponding Q27 (left side) input at that time?(Alternatively, there may be a problem with the +5V level shift at Q26 collector).Quote from: RichardM on April 10, 2022, 10:57:59 amQ28,Q29 are differential protection diodes, both inputs are connected to them symmetrically, so I don't know which you are talking about.Not sure what's +-0.8V? When is it +, when -?editI would scope between Q25 and Q27 while triggering from U5 output on the second channel. If the output follows the input to a few mV, the amp is good and something is distorting the incoming signal in this maze of JFETs. If there is severe offset or the signals don't even track each other despite both being close to ground (within the normal common mode range), then the amp is suspect.Also, R21 has to be good for this to work and there should be no differential voltage across it at any time (it just conducts Q27 right base current).Things could be easier if the instrument can be manipulated to apply 0V or similar DC to this board's input.

author: RichardM
author_rank: Frequent Contributor
timestamp: April 10, 2022, 12:45:11 pm
content: Thanks for your expertiseQ30 collector on bad module is a square pulse -0.8V to -0.5VI also realised now I had probes connected with a 67k resistor which may affect the readings. The 67k was just what I had laying around.I will probe between Q25 and Q25 as you suggest.The amp as MC1436 I believehttp://www.elektronikjk.pl/elementy_czynne/IC/MC1436G.pdfRichard

author: m k
author_rank: Super Contributor
timestamp: April 10, 2022, 03:03:30 pm
content: Where's your troubleshooting thread?U5 pin 6, TP3, RT5 output is a collective route for everything.The thing is also a multiplexer so processor is involved.Means that it's chopping time and putting different things in slots.You have (on/off)D5 Ext Ref HiD4 Ext Ref LoD3 input signalD2 Filter YD1 Filter ZD0 no filterHow voltage/current behave with different filter modes?Do you know how D0 and D3 are timed?

author: RichardM
author_rank: Frequent Contributor
timestamp: April 10, 2022, 09:27:07 pm
content: Quote from: m k on April 10, 2022, 03:03:30 pmI thought my troubleshooting methodology was sound. I am using the same unit and swapping the filter modules in and out and making sure the unit is in the same state each time. The first thing I checked was the Test Points and TP5 was very low. TP4 and the signals in and out of U1and U2 are the same between the filter modules. I then tested all the other inputs from the bus and these all look the same. I had concluded from the above that the MCU is not a factor. All these tests are reflected as green in the figure above. Is my methodology sound ?RegardsRichard

author: RichardM
author_rank: Frequent Contributor
timestamp: April 11, 2022, 09:28:11 am
content: Quote from: magic on April 10, 2022, 11:40:48 am"I would scope between Q25 and Q27 while triggering from U5 output on the second channel. If the output follows the input to a few mV, the amp is good and something is distorting the incoming signal in this maze of JFETs."The output from U5 follows the input closely on the bad module. The output is a square pulse -20.8V to +0.4V.The output from U5 follows the input closely on the good module. The output is a square pulse -20.8V to +18.4V.Regards,

author: m k
author_rank: Super Contributor
timestamp: April 11, 2022, 10:07:56 am
content: Quote from: RichardM on April 10, 2022, 09:27:07 pmYou don't know how Q0-5 are timed if you're not comparing them.I read that fast filter is the default one.So your voltages are passing that bypass route just fine.Have you tried different filters?Bottom left of schematics has a table how signal path is selected.

author: RichardM
author_rank: Frequent Contributor
timestamp: April 11, 2022, 11:45:00 am
content: Quote from: m k on April 11, 2022, 10:07:56 amOk, I think I understand what you are suggesting. I will investigate the timings further. Thankyou.

author: magic
author_rank: Super Contributor
timestamp: April 12, 2022, 04:09:21 pm
content: Quote from: RichardM on April 11, 2022, 09:28:11 amThis looks like the follower amp is functional, at least in some basic sense.m k made right observation that the circuit's function is described at the bottom: there are three signal inputs of which one should be selected at a time and two filters which can be optionally switched into the signal path and U1,Q1~Q12 are involved in selecting them.A few words about circuit operation:The JFETs on the left with source-drain shorts are used as diodes (polarity as indicated by the arrow). Make sure that the voltages regulated by those zeners are the same on both boards and that they don't "jump" in response to input signals, unless the good board also does.The rest of JFETs are used as switches: shorting their gates to -30V makes them open circuit (for signals higher than -30V), allowing resistors to pull up the gates to signal voltage level (taken from the follower amp) turns them into basically resistors.The first three JFETs select which input is enabled; their right sides are all shorted together.The next three pairs of JFETs select a filter (or lack thereof); their left sides are all shorted together and right sides feed the follower amp.You basically have to scope around and find out if the signals coming to the board are good in the first place and if all the switching stuff (those BJT pairs and JFETs) works correctly and where the signal gets different on the bad board.

author: floobydust
author_rank: Super Contributor
timestamp: April 12, 2022, 08:09:31 pm
content: Another approach is seeing if the input impedance has gone low due to a failed JFET - gate shorted to D/S. I think R1 surge-resistor carbon 6k2/R3 51k1 should have no real voltage drop across it, but it will if a shorted JFET is loading down that line or trying to put -30V to the D/S. Same for REF Hi and REF Lo, look for a shorted protection JFET as if this unit was overloaded on ACV.I would try pulling out/lifting a gate leg on a few JFETs to test them, and change to using a sine-wave or straight DC and recording voltages up to Q27.Or do comparison ohmmeter readings between the two boards. It's not easy troubleshooting because the JFETS have common connections, so narrowing it down to the exact component based on measurements might burn up one's patience.

author: RichardM
author_rank: Frequent Contributor
timestamp: April 14, 2022, 10:14:13 am
content: I thought this maybe a easy repair for a hobbyist given I have a fully functional second unit.I enjoy the learning experience. It must be a delicately balanced circuit for the active filter module.I pulled Q18, 25 and 32 and they test ok in the curve tracer. They are by no means great matches, a bit like many transitiors. I wonder how well matched they need to be ?I feel like I have probed resistances between both boards without finding any huge variations. Diode tests of all the Jetstar and transistors also appear consistent between both filter modules and no shorts have jumped out at me.I did also test Q27 in circuit with my curve tracer and in the filter that does not work correctly the transistor appears down in gain at low base current. Would this be critical ?I will keep probing as per suggestions. Thankyou.

author: RichardM
author_rank: Frequent Contributor
timestamp: April 15, 2022, 12:21:46 am
content: I have tested the dual suoer beta transister Q27 (IT1099) in circuit and attached the results. I normally pull transistors out for testing but I am concious of pulling pads from the old circuit boards. Q27+ and Q27- are as shown in the schematics above.There is a noticeable difference between the good and bad active filter module measurements but whether this makes a difference of is affected by components downstream is above my knowledgeAny comments always welcome.Richard

author: m k
author_rank: Super Contributor
timestamp: April 16, 2022, 09:58:37 am
content: Have you tried those other filters?

author: RichardM
author_rank: Frequent Contributor
timestamp: April 16, 2022, 01:42:19 pm
content: I tried changing filter modes and it made no difference to the general behaviour. I am unsure where and what to probe when changing filter modes ? Opamp outputs ? The timing somewhere ?

author: m k
author_rank: Super Contributor
timestamp: April 16, 2022, 03:51:38 pm
content: It seems that Ohms is not using default fast filter but can't confirm.I have a recollection that high ohms is unfiltered but it can be from somewhere else.Store 1 Filter uses your suspicious bypass route.Toggling the filter button is toggling between slow and fast filter.If your volts and amps are fine then everything after filter selection is also fine.Everything before filter selection can also be fine.So Q27 is fine and Q18 is not blocking.Testing Q18 side selections is easy if you have Ext Ref connectors installed.Just connect something, select and see the correct result.There input is multiplexed, all 3 are measured in one pass.For filter selections you have test points C1/2, C5/6 and C15.You should see how signal come and go when you switch between filters.If needed you can poke U6 pins and check how path selection happens.Use DC volts mode.My only Ohms controller is disconnected and "far away" so can't check how it behaves.Can't find anything rejecting filters with it either.So when you're done with DC volts compare results with Ohms.

author: RichardM
author_rank: Frequent Contributor
timestamp: April 17, 2022, 09:51:12 am
content: "Store 1 Filter uses your suspicious bypass route. Toggling the filter button is toggling between slow and fast filter."Quick update as I continue to probe.Whilst in DC Volts the volatge readings are fine for F (slow filter), F0 (fast filter), F2 & F3. The DC voltage reading is NOT correct in F1 (filter bypass) mode.The external reference works as expexted on the good unit but the bad unit reads random numbers like 0.0001321E^6Richard

author: RichardM
author_rank: Frequent Contributor
timestamp: April 18, 2022, 08:30:58 am
content: I think the only thing left for me to do is pull all the jfets and check them one by one.I have probed resistances all over the good filter board and bad filter board and they compare wellI have replaced U5 and that made no differenceI have replaced Q6 and Q12, no difference.I have checked all transistors and diodes in circuit and all appear fineVolatges rails also okMy latest probe test was to set the unit in DC volts, probe Q12 collector whilst setting filter to F1 (bypass). The good unit sees the volatge move from -30V to +4.8V. The bad unit sees the volateg move from -30V to around +0.4V ?

author: Kleinstein
author_rank: Super Contributor
timestamp: April 18, 2022, 10:09:08 am
content: When the fitler is set to bypass, the colector of Q12 should go to the votlage of the buffer amplifier output, normally the voltage the DMM reads.The filter channels should be similar: -30 V when off, and the buffer output, when activated.

author: RichardM
author_rank: Frequent Contributor
timestamp: April 18, 2022, 10:47:31 am
content: Quote from: Kleinstein on April 18, 2022, 10:09:08 amOK, thankyou . So my probing was with +5V DC on the inputs which explains the 4.8V on Q12 collector ? What could be the reason for only 0.4V (not 5V approx) on Q12 in the bad filter module ?FYI, all the Jfets tested fine on the curve tracer. All 15 of them !! I note thy are market SF 2799.Richard

author: magic
author_rank: Super Contributor
timestamp: April 18, 2022, 11:48:15 am
content: Possibly reverse breakdown of one of the JFETs that are driven to -30V or the signal coming from the left side of the board is 0.4V in the first place. Trace where 0.4V is coming for, check for voltage drops across all those series resistors.

author: RichardM
author_rank: Frequent Contributor
timestamp: April 18, 2022, 12:34:17 pm
content: Thanks, I will follow the 0.4V.I am finding it hard to reconcile why the Ohms Module readings are so random on all the filter settings F0 to F3 and DC volts is fine unless the filter is set to bypass F1.Cheers

author: m k
author_rank: Super Contributor
timestamp: April 18, 2022, 02:09:48 pm
content: Well, at least you have some JFET tracer pictures for future reference.Your Ext Ref reading indicates that signal is over voltage protected or very small signal / very big Ext Ref.I assume those colored schematics greens are from no Ext Ref situation.How are those CR1 and CR2 zeners?Check also some timings.When Ext Ref is not used Q3 is always on, it's clearly fine then but with Ext Ref something happens.Q3 can be lagging but Q0 can't, it would finally be ok, but it can be connected to that Ext Ref situation and give that high omhs all the time, obviously only if filter is bypass all the time.So first check that there are no extra lines activated when filter bypass is on and Ext Ref is off, no timing needed, U1 74174 clear is not used, so outputs are steadily what they are.Then check that Q3 is not lagging by putting Ext Ref on and checking how Q3 changes with rising edge of pin 9.

author: RichardM
author_rank: Frequent Contributor
timestamp: April 18, 2022, 09:28:48 pm
content: I haven’t pulled CR1 or CR2 but the voltages either side are the same for the working module Andy the bad module. A DMM diode check also indicates they are ok.I will try to probe a small you suggest. Should I do this in DCV or OHMS mode ?Thanks again

author: RichardM
author_rank: Frequent Contributor
timestamp: April 18, 2022, 09:58:32 pm
content: There is a bit of variation in the J086/2086 JfET traces, particularly the last one ?

author: Kleinstein
author_rank: Super Contributor
timestamp: April 19, 2022, 06:58:15 am
content: The JFETs are uses as switches and not as linear amplifiers. The JFET traces look OK and show working jFETs. However this part is not relevant for use as a switch. For the use as a switch the main relevant part is getting low gate leakage even with a relatively high gate voltage (e.g. up to 50 V in this circuit). A possible failure mode is a reduce reduced break-down voltage for the gain.The other property would be the DS leakage when the fet should be off, though this should cause less of a problem.A point to check may be the voltage at the collector of Q10 when the FETs are removed (may need a ground connection (like 100 K to ground) for the follower input if all 6 fets for the fitler settings are removed).

author: m k
author_rank: Super Contributor
timestamp: April 19, 2022, 10:03:55 am
content: Quote from: RichardM on April 18, 2022, 09:28:48 pmUse DCV with meaningful signal, 10V is up side of X1 range, including meaningful Ext Ref.Start with standard fast filter and Ext Ref off.Put 1st scope channel to C1/2.You should see your signal all the time, nothing is changing the signal path so you can also check how those bipolars are operating.You should also write down some truth tables, there are quite many things to remember.Then poke Ext Ref on.Now your 1st scope channel should see 3 different levels, that didn't happen last time.You can now use the 2nd scope channel and check where those missing ones are, leave the 1st channel to be a sanity check, assuming there still are sane Ext Ref levels.You can poke Ext Ref and Filter buttons freely, this is a pure digital tech on/off switching situation.Signal path selection can also be different than expected, so check selections all the way back to U1.Don't forget that the problem can also be a trace and not a component.

author: RichardM
author_rank: Frequent Contributor
timestamp: April 21, 2022, 12:18:33 pm
content: OK, that was a bit of work. Checked all the timings and the good and bad unit are the same, see attached.Where does that leave me ? One of the 15 Jfets are leaky ?Richard

author: m k
author_rank: Super Contributor
timestamp: April 21, 2022, 07:14:08 pm
content: I had no idea what exactly happens during Ext Ref, now we know.Good to also know that it's all rational.Since you've left signal values out I assume there were too many actual levels.Switch to Ohms, select 1M range and measure a bit less than 10M resistor.Use default fast filter and check it actually is that and not bypass, like in Ext Ref situation.Your RT6 should pulse +/-18,5V.(manual picture 602-3. Timing)Your earlier Error 6 is hinting that incoming 18,5V is dropping too fast but accurate DCV is pointing elsewhere.Some DC 10V range fast filter errors would be nice, are there any?

author: RichardM
author_rank: Frequent Contributor
timestamp: April 21, 2022, 10:09:32 pm
content: All the voltages are 0 to +5V in the tables. V=10V at inputs and Vext=15V at tear.I am going to check Q1 to Q4 transistors now.All the DC voltage DMM readings are fine except when when Vext is on or Bypass from memory.

author: m k
author_rank: Super Contributor
timestamp: April 22, 2022, 06:12:45 pm
content: There's practically only C15 left.Have you checked the continuity of the bypass route?

author: RichardM
author_rank: Frequent Contributor
timestamp: April 22, 2022, 09:17:43 pm
content: When I select bypass F1 in DCV mode the input RT6 measures at 28.7V on the broken filter module and large voltage drops are on R1 and R3 wrt TP1 The good module just reads the 10V input value. This is really confusing me

author: RichardM
author_rank: Frequent Contributor
timestamp: April 22, 2022, 11:58:51 pm
content: Quote from: m k on April 22, 2022, 06:12:45 pmC15!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!Measures 2.2nf 66 Ohm ESR but < 100 Ohm resistance across it.It didn't look suspicious when I measured it in circuit from memory. Rookie error I suspect, although I had thought these poly film caps are generally not the source of concern. Lesson learned I suppose.My 8502a is now working in DVC & OHMS mode, now to run it through some tests. Sure to be another error thrown upThe poor old filter module has been pulled in and out a thousand times and almost every component desoldered and resoldered/replaced. It has lost a few pads in the process.Thank you all for your assistance and hanging in there with a beginner.Richard

author: m k
author_rank: Super Contributor
timestamp: April 23, 2022, 01:20:51 pm
content: Practice is always good.It's also easily misleading that this module has logic Vcc actually -15V and so R(TP1) is -20V.If you one day return to that area you could check how Ohms mode is using filters.I read that filters are always free to use.Now it seems that Ohms is bypassing all the time.