HP9100B: transistor specs needed

[isanchez]

Hi,
This week-end I have been trying to repair my HP9100B, or at least to identify the problems...With the great and valuable help of James (see his post about the repairing process of his 9100A) I believe I have made great advances.

Now the display works (only a spot was shown before). It shows very well focused three lines, but with nonsense content...(see picture). It reacts to any keyboard entry, even the programme/run switch...but with nothing readible.

Checking the transistors I found two of them that, when touched, made the display flick, and even turned it off permanently. I suppose this can be one of the reasons of the failure (I wish the only one!). I enclose a picture with the location of the transistors. They are in the most left side board, the one screwed, not the easily removable.

May I kindly ask your help to identify the characteristics of these two transistors? Where can I get spares?

I appreciate very much your help...like always.

Best regards

Ignacio

[jebem]

Having zero information on that particular machine, this is what I would do:

- power on the machine.
- take readings of the voltages presented to all those transistors in the 3 legs.
- identify the transistor layout, meaning to find the emitter, base and collector pins. There are several methods to do this, the basic one is to remove one of the good ones and using a digital ohmmeter in diode checking find out the two junctions and note the forward voltage readings; a regular junction well show about 0.5V, a Darlington will have a much higher value at the Base-Emitter junction. Also check the reverse volage readings for leaks. But of course a transistor checker would be highly recommended, as it will give you the transistor type and its static gain (at least).
- draw a partial schematic of the transistor connections in the PCB.
- at this point there is enough information to identify the transistor basic characteristics, like it is a PNP or NPN, and what is the collector to base working voltage.
- from here it is a matter of selecting one from thousands of possible matches and this is the good news! As those transistors are working as simple low frequency switches (all on saturation state or all off cut off) the only real concern that I can think of is the working voltage that in this application can be relatively high.

EDIT to add this:

I got this LCR-T6 Transistor Tester recently and it is a good option as it will identify the component by itself.

[emece67]

(04-18-2016 08:05 AM)isanchez Wrote:  I enclose a picture with the location of the transistors. They are in the most left side board, the one screwed, not the easily removable.

Do not they have any inscription on their bodies? Canned transistors usually did.

[isanchez]

(04-18-2016 09:37 AM)jebem Wrote:  Having zero information on that particular machine, this is what I would do:

- power on the machine.
- take readings of the voltages presented to all those transistors in the 3 legs.
- identify the transistor layout, meaning to find the emitter, base and collector pins. There are several methods to do this, the basic one is to remove one of the good ones and using a digital ohmmeter in diode checking find out the two junctions and note the forward voltage readings; a regular junction well show about 0.5V, a Darlington will have a much higher value at the Base-Emitter junction. Also check the reverse volage readings for leaks. But of course a transistor checker would be highly recommended, as it will give you the transistor type and its static gain (at least).
- draw a partial schematic of the transistor connections in the PCB.
- at this point there is enough information to identify the transistor basic characteristics, like it is a PNP or NPN, and what is the collector to base working voltage.
- from here it is a matter of selecting one from thousands of possible matches and this is the good news! As those transistors are working as simple low frequency switches (all on saturation state or all off cut off) the only real concern that I can think of is the working voltage that in this application can be relatively high.

EDIT to add this:

I got this LCR-T6 Transistor Tester recently and it is a good option as it will identify the component by itself.

Hi Jose,,
thanks with your instructions. I am going ahead with it. One additional question: Is it necessary to remove the transistor to determine the type PNP or NPN, with a multimeter? Even to determine if it is blown?
Thanks again for your valuable help

Kind regards

Ignacio

[isanchez]

(04-18-2016 10:34 AM)emece67 Wrote:  

(04-18-2016 08:05 AM)isanchez Wrote:  I enclose a picture with the location of the transistors. They are in the most left side board, the one screwed, not the easily removable.

Do not they have any inscription on their bodies? Canned transistors usually did.

I am going to dismount the board this evening and check it. I was afraid, from others experiences, that these have internal refereces from HP at that time. Don't know if there is any equivalency table to new models.

Thanks again for your interest.

Ignacio

[jebem]

(04-18-2016 10:37 AM)isanchez Wrote:  Is it necessary to remove the transistor to determine the type PNP or NPN, with a multimeter? Even to determine if it is blown?

Hi, Ignacio,

Well, I usually check it in circuit using a regular ohmmeter set to diode testing just for an initial check.

Depending on the results and other information available, if I still suspect it may be defective, I remove it to check off circuit. Usually in circuit testing is not reliable because if there are other components in parallel it will change the readings resulting in misleading information.

For instance, we may read a short circuit between two of the three legs but we can not conclude that the transistor is faulty because if there is a low resistance component in parallel we are in fact reading this later component.

But because that calculator has a number of identical circuits we can compare the transistor readings (voltages and resistances) in circuit for a initial checking.
But sooner or later we will need to remove the suspect component to test it of circuit.

Also, an oscilloscope, even a modest one able to display just up to 10MHz Y-channel and 1uS time base X-channel, will be of great help because we can check the dynamic behavior of those transistors as well.
However it must cope with high voltages (at least 200Volt on the Y-channel amplifier input attenuator) specially when dealing with vacuum fluorescent displays.
I would recommend a classic legacy one from the 70's as they are usually robust. They can be bought for low prices in eBay. High calibrated precision is not a must for this kind of application.

[Accutron]

Maybe this will help...

HP Transistor/Diode Cross Reference (PDF)

[isanchez]

In the transistor it can be read:
Motorola 3-203936

Regards

Ignacio

[jebem]

(04-18-2016 01:11 PM)Accutron Wrote:  Maybe this will help...

HP Transistor/Diode Cross Reference (PDF)

Thanks from my side. Huge listing!

Additionally, some links here may help as well when dealing with cross reference HP part numbers:
http://www.hpmuseum.org/cgi-sys/cgiwrap/...ead=177507
http://www.hpmuseum.org/cgi-sys/cgiwrap/...read=27258
http://www.sphere.bc.ca/test/hp-parts/300-hpxref.pdf (similar to what Accutron shared before)
http://www.hpmuseum.org/cgi-sys/cgiwrap/...ead=143168 (pls read the last post)

Small note:
To find the above links from this MoHPC, I used Google and typed:
part number equivalent site:www.hpmuseum.org
and this list can be larger if more time is spent looking for it using different words in the search.

[isanchez]

THank you all!!
I am going to start searching...
I keep you inofrmed if I succed!

Kind regards

Ignacio

[jebem]

(04-18-2016 01:51 PM)isanchez Wrote:  THank you all!!
I am going to start searching...
I keep you inofrmed if I succed!

Kind regards

Ignacio

What about the available service manual and schematics?
It should be possible to identify exactly what is the PCB with those suspected transistors, and from there we can now identify the transistor (PNP or NPN) type and function.

link1
link2
link3

[isanchez]

Yesss! it is the board 9 in the schematics
I take a look

Thanks!!

Reagards

Ignacio

[isanchez]

(04-18-2016 03:45 PM)jebem Wrote:  

(04-18-2016 01:51 PM)isanchez Wrote:  THank you all!!
I am going to start searching...
I keep you inofrmed if I succed!

Kind regards

Ignacio

What about the available service manual and schematics?
It should be possible to identify exactly what is the PCB with those suspected transistors, and from there we can now identify the transistor (PNP or NPN) type and function.

link1
link2
link3

Dear JEbem,

it seems clear now: it is board 09100-66509 left board (qualifier)...it states: "all transistors 5080-4663, except where specified"...looking at the diagram, this type of transistor is PNP type...The HP part is 1853-0203...I am going to try with an equivalent.

Now I believe I can reach the spare.

Again, you are incredible. I thank you all for your help

Kind regards
Ignacio