H9 Troubleshooting

[zen djn]

All the logic chips on the character gen board test good on my RCT Pro.  Might this be a character rom issue?  I don't have a known working rom to test in it unfortunately.  The screen does change to plot mode when the plot key is pressed.

Thanks,

--David

[glenn.f...@gmail.com]

I think that a bad ROM is a much lower probability than a bad connection, or possibly more bad chips.

 

The H9 has many, many interconnects. They are typically the number one source of problems with this device. The recommended solution is plugging and unplugging every connector (a few times to clean the contacts)  and reseating every chip. my guess would be to focus on the ram and counter board, but that’s just a guess…

 

When you’re removing each board to re-seat it you can take the opportunity to test all the chips on all the boards. Tedious but perhaps worthwhile.

 

It looks like you’re very close to getting this operational!

 

• Glenn

 

 

From: se...@googlegroups.com <se...@googlegroups.com> On Behalf Of zen djn
Sent: Monday, May 18, 2026 3:11 PM
To: SEBHC <se...@googlegroups.com>
Subject: [sebhc] H9 Troubleshooting

 

All the logic chips on the character gen board test good on my RCT Pro.  Might this be a character rom issue?  I don't have a known working rom to test in it unfortunately.  The screen does change to plot mode when the plot key is pressed.

 

Thanks,

--David

 

 

 

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[David Nowak]

Thanks for the suggestions.  I have already removed and tested every logic chip (I know that doesn't mean a partial or intermittent fault isn't present in the chips, but it's a good start), removed all the individual PCBs, cleaned all the sockets and board connections with deoxit and reassembled everything. 

I've also specifically checked and tried replacing the logic chips suggested by the service manual for that error, ie #36 "960 cursors" without change. 

-- David

To view this discussion visit https://groups.google.com/d/msgid/sebhc/321a01dce701%24b70e6630%24252b3290%24%40gmail.com.

[Dave McGuire]

Just a quick data point...The two H-9s that I've repaired both had
failed PROMs, in addition to numerous inter-board contact problems.
Test the PROMs if you can.

-Dave

On 5/18/26 21:22, David Nowak wrote:
> Thanks for the suggestions.  I have already removed and tested every
> logic chip (I know that doesn't mean a partial or intermittent fault
> isn't present in the chips, but it's a good start), removed all the
> individual PCBs, cleaned all the sockets and board connections with
> deoxit and reassembled everything.
>
> I've also specifically checked and tried replacing the logic chips
> suggested by the service manual for that error, ie #36 "960 cursors"
> without change.
>
> -- David
>
>
> On Mon, May 18, 2026, 16:05 <glenn.f...@gmail.com
> <mailto:glenn.f...@gmail.com>> wrote:
>
> I think that a bad ROM is a much lower probability than a bad

> connection, or possibly more bad chips.____
>
> __ __

>
> The H9 has many, many interconnects. They are typically the number
> one source of problems with this device. The recommended solution is
> plugging and unplugging every connector (a few times to clean the
> contacts)  and reseating every chip. my guess would be to focus on

> the ram and counter board, but that’s just a guess…____
>
> __ __

>
> When you’re removing each board to re-seat it you can take the
> opportunity to test all the chips on all the boards. Tedious but

> perhaps worthwhile.____
>
> __ __
>
> It looks like you’re very close to getting this operational!____
>
> __ __
>
> * Glenn____
>
> __ __
>
> __ __
>
> *From:*se...@googlegroups.com <mailto:se...@googlegroups.com>
> <se...@googlegroups.com <mailto:se...@googlegroups.com>> *On Behalf
> Of *zen djn
> *Sent:* Monday, May 18, 2026 3:11 PM
> *To:* SEBHC <se...@googlegroups.com <mailto:se...@googlegroups.com>>
> *Subject:* [sebhc] H9 Troubleshooting____
>
> __ __

>
> All the logic chips on the character gen board test good on my RCT
> Pro.  Might this be a character rom issue?  I don't have a known
> working rom to test in it unfortunately.  The screen does change to

> plot mode when the plot key is pressed.____
>
> __ __
>
> Thanks,____
>
> --David____
>
> __ __
>
> __ __
>
> ____
>
> __ __

>
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--
Dave McGuire, AK4HZ
New Kensington, PA

[Glenn Roberts]

How were you able to replace those? Is there a modern part equivalent?

Sent from my iPad

> On May 18, 2026, at 9:35 PM, Dave McGuire <mcg...@neurotica.com> wrote:
>
> 

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[Dave McGuire]

There is no modern equivalent that I'm awaer of, but I luckily had
some blank PROMs of the correct types.

-Dave

[Tim R]

Hi David,

Beyond the symptoms you have described, are there any functions that work? If you set it half-duplex and press an alpha key along with the "repeat" key to fill a line of text, does anything show up in the black area between the two blocks of characters?  Even though you aren't seeing a cursor, I would be curious? I had issues on my TPU board that cause some pretty strange stuff on screen. Also, do you get a beep when you do a "CTRL" G? Does the "plot", or the "SHORT FORM" key do anything.  When I worked to troubleshoot my H9, I found some good clues on where to look from seeing what, if anything did work. 

In my case, a single inverter on a 7405 chip caused chaos with my H9. By seeing the things that were working though, it focused me to the TPU PCB as the place to look. 

Tim