[ Solved ] HP 16500A to 16500B Upgrade with PC floppy drive

[davorin]

I've received a working HP 16500A today as also a 16500B CPU board last week....which is originally intended for a broken 16500B arriving tomorrow which shows a ROM failure during boot...
Also saw in the Yahoo group someone mentioning that he wants to put in the 16500-66509 CPU board into the 16500A model, which apperenty needs some rewiring for the CRT signals...

So my question... do the 16500A and 16500B CPU boards share the same pinout at the backplane?

Would be an interesting project to publish if it is feasable...also...never saw anywhere any ROM images for the 16500B CPU boards on the net...

[davorin]

Found another yahoo group posting....

https://groups.yahoo.com/neo/groups/hp_agilent_equipment/conversations/messages/30209

Though the topic describes upgrading A or B to a 16500C model, the posting itself mentions that the 16500-66509 CPU board can go directly into the 16500A...

[davorin]

Hmm...won't be easy...or doable at all when I look at the 16500A CPU board...

Just two connectors, one for floppy drives and one going to the monitor board....maybe following the tripple 4 Bit RGB D/A converter signals is a good start ;-)
I guess the two signals going via 75R resitors are the sync signals....

And pin 21 is red, 29 green and 37 blue...

[davorin]

Okay...seems the 16500A boots up without the 40-pin cable connectoed to the monitor board....as it reads from the front floppy right after powering up....

Means at least to me it didn't detect any error from the missing cable....so now let's measure the signals coming from the 40-pin connectors if there is any life besides the video signal...

Below I will document the pinout I have found so far....

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GND -  2    1 - GND
GND -  4    3 - V Sync
GND -  6    5 - GND
GND -  8    7 - H Sync
GND - 10    9 - GND
GND - 12   11 - GND
GND - 14   13 - GND
GND - 16   15 - GND
GND - 18   17 - GND
GND - 20   19 - GND
GND - 22   21 - Red
GND - 24   23 - GND
GND - 26   25 - GND
GND - 28   27 - GND
GND - 30   29 - Green
GND - 32   31 - GND
GND - 34   33 - GND
GND - 36   35 - GND
GND - 38   37 - Blue
GND - 40   39 - GND
Hmm...wonder why they wasted a 40 pin connector for just 5 signals ;-)
Anyway...makes it easier if hopefully the 16500B CPU board is really compatible to the backplane...

Below screenshot shows:

Trace 1: V Sync
Trace 2: H Sync
Trace 3: Red video

[davorin]

It is a walk in the park....upgrading a 16500A to 16500B....

Below picture of the 16500B CPU board with temporary interconnects to the monitor board...and the screen showing the 16500A with local CF card information...

Just the floppies won't work...not sure if a regular PC drive does the job....so let's find out (o;

Here's the 10-pin video connector pinout of the 16500B CPU board.

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GND - 1    2 - H Sync
GND - 3    4 - V Sync
GND - 5    6 - Blue
GND - 7    8 - Green
GND - 9   10 - Red

[davorin]

Okay...got at the point where I connected a cheap Mitsumi PC floppy drive to the CPU board...

Of course it reports an error during boot...

But when I go into the floppy menu and execute the "Load" command...the floppy drive is selected....the head moves and the green floppy LED goes on...
though it reports "no disk".....

[davorin]

Okay....now no more flexible disk error during boot....but still can't read the floppy drive....

Seems pin 2 from the floppy connector going to the /DCD signal of the WD37C65B controller plays a role that the floppy drive is recognized during boot...

Connecting to "0" the bootup only reports that no disk is present....or when accessing the disk through the menu...
Leaving then the /DCD pin unconnected, it starts to read from the floppy but reports a CRC error...

Executing "Format" results in the same CRC error.....

[davorin]

Here is the current connection diagram so far:

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7 - +5V
9 - +5V
11 - +5V
13, 15, 17, 19, 21, 23, 25, 27, 29, 31, 33 - GND
Connection from floppy connector to PC floppy drive

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2 - connect to pin 34 directly
4 - 4 /BUSY
6 - open
8 - 8 /INDEX
10 - 12 /DRIVE1
12 - open
14 - open
16 - 16 /MOTOR1
18 - 18 /DIR
20 - 20 /STEP
22 - 22 /WDATA
24 - 24 /WGATE
26 - 26 /TRK00
28 - 28 /WPT
30 - 30 /RDATA
32 - 32 /SIDE1
34 - 34 /RDY

[davorin]

Some further digging.....hooked up a floppy drive from the other 16500B analyzer...

The first screen shows the signals on pin 2, 4 and 34 when no disk is inserted.
The second screen with a disk inserted and readable.

Channel 1: Pin 2
Channel 2: Pin 34
Channel 3: Pin 4

[davorin]

Code: [Select]

Hmm...timing is okay now....you need to connect pin 2 and pin 34 together....then it detects if a disk is inserted or not...

Can see data coming from the floppy drive...but it always fails with CRC error...

Found this small note at: [url]http://www.ebay.com/gds/HP-16500-Series-Mainframe-Logic-Analyzer-Oscilliscope-/10000000009183958/g.html[/url]

[code[Note that these these floppy drives are NOT directly compatible with PC floppy drives, though PC drives can be modified to work: as per note from flamebug

So it must be possible...but looks like to modify also the drive itself...

[davorin]

Some more traces....comparing the data stream from the floppy drive on channel 3....

The first one coming from the original drive...the second one from a PC compatible drive....

[davorin]

Hahhhh...got it working now :-)

Bought two Teac FD-235HF-C110 floppy drives from Ebay....some small modifications to the jumpers/wiring...eh voilà....the 16500B CPU board can now read the floppy content...
I assume similar models (with different endings than C110) would work as well...and sometimes they do have real jumpers.

Now for some formatting, writing testing ;-)

[davorin]

Hmm..couldn't format a floppy disk...but also didn't work on a real 16500B....

But copying a screenshot over to floppy worked just fine :-)

Case closed (o;

[tautech]

Thanks for sharing. 

[davorin]

You're welcome :-)

I'll do a picture tomorrow of the floppy drive modification...also some other floppy drives should arrive soon for testing....

Just haven't tested the new fans yet how loud they are in comparison to the originals...

[reggs]

Hi davorin - Any chance you could update us on what your last few modifications were ?
You refer to 'some small modifications to the jumpers/wiring...eh voilà....the 16500B CPU board can now read the floppy content...'

I've followed your pinout above but for an HP 1661A Analyser which seems to have a similar configuration to yours, but I keep getting 'Unsupported Format' reported on the screen.

The PC drive I have now lights up and I can hear the head seek, but I can't get any further than that unfortunately