HP-97 Circuit
04-15-2021, 01:19 AM (This post was last modified: 04-15-2021 01:34 AM by teenix.)
Post: #1
 teenix Senior Member Posts: 1,717 Joined: May 2016
HP-97 Circuit
Hi all,

I found some more circuit diagram issues with the HP-97 service manual.

(1)
Q4 is supposed to be a NPN type but is shown as PNP.

(2)
There is an extra wire connects Vb to R7, Q4 emitter and Q2 base.

Modified schematic attached.

Edit:

I've posted a modified Service manual at http://www.teenix.org/97ServMan.pdf

It also has cleaned up oscilloscope images.

cheers

Tony

Attached File(s) Thumbnail(s)

04-15-2021, 07:47 AM
Post: #2
 AndiGer Senior Member Posts: 464 Joined: Oct 2015
RE: HP-97 Circuit
Hi Tony,

Once I found that in figure 4-10 (page 53 in the pdf file) Q2 and Q3 are switched.
Maybe you change in your pdf version.

Andi
04-15-2021, 10:03 AM (This post was last modified: 04-15-2021 10:39 AM by teenix.)
Post: #3
 teenix Senior Member Posts: 1,717 Joined: May 2016
RE: HP-97 Circuit
(04-15-2021 07:47 AM)AndiGer Wrote:  Hi Tony,

Once I found that in figure 4-10 (page 53 in the pdf file) Q2 and Q3 are switched.
Maybe you change in your pdf version.

Andi

Hi Andi,

I looked at the circuit in my PDF copy and Q2 (1854-0668) base is connected to Q3 (1854-0071) collector. This seems to match the components on the PCB where each transistor is marked 4-668 (Q2) and 4-071 (Q3).

Edit,

I notice in the brouhaha.com HP chips, it has 1858-0044 (quad NPN, anode driver, print head driver, print motor driver) listed equivalent as TPQ3904, but I don't think this can handle up to 500mA for the print heads. 2N3904 would be a discrete transistor equivalent, but current is around 100-200mA. Maybe something like PN2222A or similar (800mA). MMPQ2222A is a quad package but surface mount and different pinout.

cheers

Tony
04-15-2021, 03:31 PM (This post was last modified: 04-15-2021 03:32 PM by AndiGer.)
Post: #4
 AndiGer Senior Member Posts: 464 Joined: Oct 2015
RE: HP-97 Circuit
Hi Tony,

Re-checked with old and new layout of the PCB - yes, you are right. Must have been dreaming when I meant I found that :-).

But there are other mistakes in the Service Manual.

In figure 4-9 U7 to U9 are marked as ROM3 thru ROM5 whereas due to table 4-6 there is no ROM4. U9 due to its position in figure 4-9 should be 1818-0233 i.e. ROM3. It is wired totally different compare to the other four ROMs.
Pin connections of U5 to U8 are all the same and connected to the corresponding pin between each other as seen in figure 4-10. So the position of these chips doesn't matter (if pin orientation is ok).
In figure 4-10 U7 is marked ROM5, U8 ROM6.

So we get a mix-up of table 4-6, figure 4-9 and figure 4-10.

In a real calculator I found 1818-0230 at position of U7 of figure 4-9, 1818-0229 at position of U8.
Due to the mix-up I can't tell neither 1818-0230 is ROM5 or ROM6 nor for 1818-0229.

Andi
04-16-2021, 05:14 AM
Post: #5
 teenix Senior Member Posts: 1,717 Joined: May 2016
RE: HP-97 Circuit
Hi all,

I updated the HP-97 PCB overlay and updated the service manual.

http://www.teenix.org/97ServMan.pdf

cheers

Tony

Attached File(s) Thumbnail(s)

04-16-2021, 06:59 PM
Post: #6
 AndiGer Senior Member Posts: 464 Joined: Oct 2015
RE: HP-97 Circuit
Tony,

In table 4-6 you should also interchange U7 and U9 (as U9 is 1818-0233 = ROM3)
04-16-2021, 09:15 PM
Post: #7
 teenix Senior Member Posts: 1,717 Joined: May 2016
RE: HP-97 Circuit
(04-16-2021 06:59 PM)AndiGer Wrote:  Tony,

In table 4-6 you should also interchange U7 and U9 (as U9 is 1818-0233 = ROM3)

All done and uploaded again.

cheers

Tony
04-17-2021, 08:54 AM
Post: #8
 AndiGer Senior Member Posts: 464 Joined: Oct 2015
RE: HP-97 Circuit
(04-16-2021 09:15 PM)teenix Wrote:
(04-16-2021 06:59 PM)AndiGer Wrote:  Tony,

In table 4-6 you should also interchange U7 and U9 (as U9 is 1818-0233 = ROM3)

All done and uploaded again.

cheers

Tony

Thank you, saved locally :-)
04-27-2021, 11:00 AM
Post: #9
 Siegfried Member Posts: 111 Joined: Jan 2014
RE: HP-97 Circuit
Thanks for your work. Finally need to open up my 97 and try to fix it.
10-11-2021, 05:15 PM
Post: #10
 hpux735 Junior Member Posts: 29 Joined: Oct 2021
RE: HP-97 Circuit
(04-15-2021 10:03 AM)teenix Wrote:  I notice in the brouhaha.com HP chips, it has 1858-0044 (quad NPN, anode driver, print head driver, print motor driver) listed equivalent as TPQ3904, but I don't think this can handle up to 500mA for the print heads. 2N3904 would be a discrete transistor equivalent, but current is around 100-200mA. Maybe something like PN2222A or similar (800mA). MMPQ2222A is a quad package but surface mount and different pinout.

cheers

Tony

Hi Tony (and all),

I'm very new here, and have an HP-97 that I inherited from my Wife's grandfather. I've been able to get it basically running, but it has segment f lit on all segments on the display. I gather from Tony's excellent notes document that this is due to a failed anode driver IC. I'm guessing by the discussion about replacing the quad transistor IC with discrete transistors implies that an equivalent is unobtanium?

Yesterday, I fixed the printer, and while that works (using the sanding the tires method) the printout is fairly faint. Is that likely from old paper, or should I replace R8?

Thanks!
- Will
10-11-2021, 07:02 PM
Post: #11
 Kees Bouw Member Posts: 66 Joined: Jul 2017
RE: HP-97 Circuit
(10-11-2021 05:15 PM)hpux735 Wrote:  Yesterday, I fixed the printer, and while that works (using the sanding the tires method) the printout is fairly faint. Is that likely from old paper, or should I replace R8?

For me, it was the paper. Old paper is no good, fortunately new rolls with the correct width are still available and you should definitely use those to further troubleshoot the print quality.
10-11-2021, 07:09 PM
Post: #12
 Kees Bouw Member Posts: 66 Joined: Jul 2017
RE: HP-97 Circuit
(04-15-2021 01:19 AM)teenix Wrote:  I've posted a modified Service manual at http://www.teenix.org/97ServMan.pdf

On this topic... does anyone know of a service manual for the HP-67? Did it ever exist and if so, is there still an original or a copy left somewhere on this planet?
Also, every scan I have seen of the HP-97 service manual is pretty bad in quality. Probably they are all essentially the same scan. Does anyone possess an original and would be willing to re-scan it with modern equipment?
10-11-2021, 07:59 PM
Post: #13
 Eric Rechlin Senior Member Posts: 423 Joined: Dec 2013
RE: HP-97 Circuit
(10-11-2021 07:09 PM)Kees Bouw Wrote:
(04-15-2021 01:19 AM)teenix Wrote:  I've posted a modified Service manual at http://www.teenix.org/97ServMan.pdf

On this topic... does anyone know of a service manual for the HP-67? Did it ever exist and if so, is there still an original or a copy left somewhere on this planet?
Also, every scan I have seen of the HP-97 service manual is pretty bad in quality. Probably they are all essentially the same scan. Does anyone possess an original and would be willing to re-scan it with modern equipment?

I am expecting to receive an HP-97 service manual in the mail soon and I will produce a high quality scan of it. I will also attempt to incorporate teenix's corrections when I do this.
10-11-2021, 08:03 PM
Post: #14
 hpux735 Junior Member Posts: 29 Joined: Oct 2021
RE: HP-97 Circuit
(10-11-2021 07:02 PM)Kees Bouw Wrote:  For me, it was the paper. Old paper is no good, fortunately new rolls with the correct width are still available and you should definitely use those to further troubleshoot the print quality.

Awesome. Just what I wanted to hear. I've just finished refurbishing the card reader, and it seems like it's in good shape. Fingers crossed!
 « Next Oldest | Next Newest »

User(s) browsing this thread: