Threaded Mode | Linear Mode

teenix · (This post was last modified: 04-18-2022 11:52 AM by teenix.)

Hi all,

I'm looking at a HP-97 for someone with a dim display and it needs one or two transistors replaced. One is a current bypass for the charger which has the casing face detached, probably from overload and the other one supplies current to the anode drivers.

1853-0393 and 1853-0374 both PNP's.

Funnily enough, these parts, and parts I've searched for in the past using the HP X-Ref file, yielded no matches.

I've seen previous posts discussing parts matches but I cant locate them.

Any ideas - probably general purpose PNP's will do - 2N2907 etc.

cheers

Tony

AndiGer · 04-18-2022, 12:22 PM

(04-18-2022 11:51 AM)teenix Wrote: Hi all,

I'm looking at a HP-97 for someone with a dim display and it needs one or two transistors replaced. One is a current bypass for the charger which has the casing face detached, probably from overload and the other one supplies current to the anode drivers.

1853-0393 and 1853-0374 both PNP's.

Funnily enough, these parts, and parts I've searched for in the past using the HP X-Ref file, yielded no matches.

I've seen previous posts discussing parts matches but I cant locate them.

Any ideas - probably general purpose PNP's will do - 2N2907 etc.

cheers

Tony

Correct - 2N2907 will do. Replaced on the keyboard PCB once and noted inside my printed service manual :-).
N.B. 1854-0071 replaced by 2N2222

Andi

teenix · 04-18-2022, 12:45 PM

Thanks Andi,

There is a place nearby that has them.

cheers

Tony

teenix · (This post was last modified: 04-19-2022 03:14 AM by teenix.)

Hi all,

I got stung trying to trace the transistor legs because the 97 service manual from here...

https://literature.hpcalc.org/community/hp97-sm-en.pdf

It still has an incorrect connection between R7 and VB on the display/key PCB.

Also, the parts list has R3 and R4 reversed.

I got hold of some 2N2907 transistors but I measured the 8R2 2W resistor (marked as R4) and this is open circuit. This resistor is marked as "fusible", so I guess the charger circuit was exposed to a nasty voltage and blew the transistor flat face off and blew the fuse as well.

I cannot find any mention of the current that would flow through this resistor and I don't know what current the battery is charged at. This resistor carries the high charge rate current, while a series 4R7 2W resistor is placed in series while the power switch is ON and reduces charge.

I guess for a max 2W resistor, SQRT (2W / 8R2) = somewhere around a 500mA fuse.

I guess I could solder the internal wire from a glass tube 500mA fuse in series with a new 8R2 resistor.

cheers

Tony

Dreato · 04-20-2022, 03:32 PM

I had the dim display problem recently, too. I replaced all 3 transistors (Q 2, 3 and 4) with generics: 2N3906 (I had a bunch of these) for Q 3 and 4, and MPSU56 for Q2. This last is an audio transistor I had on hand, but it worked fine.

The original Q 3 and 4 tested bad, but Q4 was fine, so I kept it in the parts box.

This leads me to a question: Generics have worked for me in many HP applications over the years. In this case, Q 3 and 4 have different parts #s. Do you think they actually have significantly different specs?

What does everyone think??

teenix · (This post was last modified: 04-20-2022 09:27 PM by teenix.)

Q1 PNP passes the battery charge current under heavy display current demands
Q2 PNP passes the display current (larger tabbed transistor)
Q3 PNP display current monitor and switch for Q4
Q4 NPN switch for Q1

Q3 and Q4 probably similar specs.

Note: If you changed NPN Q4 with a PNP 2N3906 it won't work properly, although your text may have a typo.

cheers

Tony

(04-20-2022 03:32 PM)Dreato Wrote: I had the dim display problem recently, too. I replaced all 3 transistors (Q 2, 3 and 4) with generics: 2N3906 (I had a bunch of these) for Q 3 and 4, and MPSU56 for Q2. This last is an audio transistor I had on hand, but it worked fine.

The original Q 3 and 4 tested bad, but Q4 was fine, so I kept it in the parts box.

This leads me to a question: Generics have worked for me in many HP applications over the years. In this case, Q 3 and 4 have different parts #s. Do you think they actually have significantly different specs?

What does everyone think??

Dreato · (This post was last modified: 04-21-2022 09:01 PM by Dreato.)

You're right - typo. I should have said "Q2 was fine". That's my mistake quota for the day! Q1 - Q4 are all PNP.

Dreato · 04-21-2022, 09:28 PM

Further update. There are 2 versions of this board, one presented in the 1976 service manual (Board part # 00097-60002) and the 1982 service manual (board part # 00097-60910). Both manuals show Q4 as part # 1854-0071, but in the 1976 manual it's an NPN, and in the 1982 manual it's a PNP. The schematics are slightly different, too.

Any ideas?? I can't check the old transistors I removed - the tester showed them both at a pair of series resistors.

teenix · 04-21-2022, 10:21 PM

I'm pretty sure PNP is a typo.

My el cheapo transistor tester displayed series resistors as well.

Attached is a display/key board circuit (error - top) and (corrected - bottom). As mentioned earlier, R3 and R4 reversed in the parts list, so the document does have an error or two.

cheers

Tony

AndiGer · 04-22-2022, 02:39 PM

See here - message #4 by Tony - but Tony Duell :-D.
1853-xxxx = Silicon PNP
1854-xxxx = Silicon NPN

Dreato · 04-22-2022, 04:52 PM

@AndiGer - Good memory to remember a post from 2011!

The 97 manuals contain typos about the Keyboard Q4:

1976 manual - Q4 = 1854-0071 PNP
1982 manual - Q4 = 1854-0071 NPN

I still don't know which one is correct. I'll pull one from working 97 and check. Based on my distant discrete transistor knowledge from the 1970s (!!), I think it's NPN. This means the 1976 service manual should read Q4 = 1854-0071 NPN.

Is this correct? Please see Tony Nixon's other corrections.

Dreato · 04-22-2022, 09:42 PM

I think this is the last post for me on this confusing subject. I pulled Q4 from a working 97, and it's NPN. I checked the tracing on both the older and newer boards, and they're the same. The 1976 service manual is correct. The 1982 manual has a number of errors.

1) The keyboard PCA is part # 0097-60019 (the manual has 60910)
2) Q4 is NPN (manual has PNP)
3) Q2 base is connected to R7, but NOT connected to Vbatt.

My conclusion - Tony Nixon was correct on all counts (not surprised!).

Best Regards to all,
Dave

AndiGer · 04-23-2022, 06:17 AM

1854-0071 is used several times inside the 97.
Card reader Q1, keyboard Q4, logic Q3.
In all tables in the 1976 manual it is listed to be NPN
The only confusing is the error in figure 4-23 where it is drawn to be PNP.

Tony (Nixon) once did some corrections to the manual and published on his website.
See the picture Tony posted before