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HP85 probs (Printer/Screen/Cassette)



#2

i recently found a hp85 in very good shape. It works so far, the test is finished without error. BUT... there is the letter M in column 8 and row 1,3,5,7,9,13 on the screen. These letters can't be cleared, and if i try to overwrite them they change to "`". Very odd. Does anybody have a good hint for me?

Also the printers belts are nearly finished (it prints but with some noises), some "teeth" of the belt are missing already. Does anybody know how to fix the belts (maybe there are other belts on the market which can be used).

The same goes for the drive roller of the casette drive.

Any help highly appreciated. Thanks.
Arnd


#3

The video problem sounds like bad video RAM or a problem with the rest of the video generating circuit. On the grounds that the latter is almost certainly inside an HP custom chip while the former could well be standard parts, I would check/replace the RAM first.
Sorry I can't be more help -- if necessary I'll get out one of my HP85s and look at the PCBs for you.
I believe the printer belts _are_ standard parts. I am not sure where you can get them from, but I know somebody who got a set (not from HP) a couple of years ago.


#4

Yes, Tony is correct, the belts are standard parts, made by Chemi-Flex (www.chemiflex.com).

I wrote to them just about a week ago to inquire about where to buy their belts, but have not yet heard back from them.

The part numbers (taken from the HP85 belts themselves) are:
175T80 and 78T80.

If you are able to take these part numbers and reach Chemi-Flex sooner than I am or find a distributor, please post a response here to help the rest of us out! I'll do the same! Good luck!

p.s. Another HP user told me he used heat shrink tubing to repair the capstan on the HP85 casette drive...


#5

thank you for your help. Tony can you help me locate the video ram?


#6

OK... It'll take a couple of days, but I'll dig out an HP85, pull the case and see what I can work out.


#7

The video RAM consist of 5 ICs on the logic PCA U12 crt control U13-U16 crt RAM(s)

JR


#8

Thanks, that's saved me from digging out an HP85 and taking it apart.
Can I confirm that U13-U16 are the RAMs, and that U12 is the video display controller chip (and not a RAM). That's what you seem to imply, but then you say there are 5 RAMs.


#9

Tony, yes you are correct. U12 is the video controller and U13-U16 are the RAMs

JR


#10

I just picked up an HP-85 this week, and everything seems to work fine except for the the tape drive. When I try to load standard pac software, I get an "error 74: stalled" message. Is this that tape capstan problem I've been reading about?

One piece of info that might be useful to people here: As near as I can tell, the tapes used by the HP-85 are identical to the cartridges used by the DEC TU-58 serial tape drive found on some PDP-11's. The cartridge looks exactly the same, and I believe it is also a 780? record 192K tape.


#11

That does, indeed sound like a capstan problem. I assume you can hear the tape drive motor running, and that the tape will move if you
turn the drive puck (the wheel in the catridge that engages with the capstan) by hand. Jammed cartridges (the tape sticks to the drive belt) are not unknown.
AFAIK, the TU58 cartridge is the same mechanically, but the TU58 drive needs a cartridge that's been
factory-formatted (by DEC). You can't format the cartridges on a normal TU58 drive. Some of us (myself for one) are also PDP11 and VAX enthusiasts, and getting suitable media for the TU58 is difficult/expensive now (I've seen prices of >$100 per cartridge). So I guess I am saying don't _needlessly_ reformat TU58 tapes. If you need a tape for an HP85 and have an old TU58 lying around, use it. But don't reformat an entire box of them until you need each one.


#12

Interesting...I sold off all the TU-58 drives I had, but I still have a box of 50 or so cartridges in case I can find another drive sometime.

I opened up my 85, and the capstan is indeed in need of a new rubber part. I think I'll try the heatshrink tubing method somebody suggested. Naturally, the printer belts are also melting to goo, so I'll have to try to get in touch with the place that still sells suitable belts.

#13

Hi Chris!

Just wanted to let everyone know that the urethane-kevlar belts that you recommended from www.beltcorp.com work GREAT!

I also replaced my capstan cover with some shrink tubing as recommended by Vassilis Prevalakis. However, I, too am getting the "stalled" error message.

I had been able to rewind that tape on another HP85 that I have, but now that one won't budge it either - it too says "stalled."

I even tried following the procedure for opening up the tape and checking the tape winding.

I'm curious - does, perhaps, the HP85 read some sort of timing from the magnetic tape? Could it be that the tape itself is bad and not sending the proper timing back to the HP85? Perhaps a goofy theory, but I don't see why the tape worked at one point on one HP85 and then didn't shortly thereafter.

Maybe someone else knows or has some ideas...

-Mike


#14

Mike--the "stall" errors (tape transport error caused by motor overload) which points to a bad tape or problems with the drive itself. Is it possible that the heat shrink used to "resurface" the capstan is to thick and causing the problems. Or the tape transport needs alittle tweeking?

Try using the CTAPE (Condition Tape)

JR


#15

JR-

I was wondering a bit about the shrink-tubing, so what I did was remove the tape from the drive and manually pushed the two "nubs" at the back of the drive to turn the switch on that makes the unit think that it has a tape in. Then I tried the CTAPE command and REWIND to see what would happen.
The motor would start to spin and then it'd say STALLED.
Hence, even without load, the motor is stalling.

Perhaps it is a bad motor? (Except that the one that had worked is now reporting stalls, and they BOTH start to turn.)

Anyway, that is what got me to wondering how the 85 "measures" stalling and made me wonder if there is some information that gets written and read back (like the old analog tape decks that would monitor what was recorded) to determine speed. I was speculating that if the tape were stuck this way of measuring stall would determine that the tape hadn't moved, and it would also explain why, when I remove the tape completely and run the commands, I still get "stall."

That's why I asked. As I indicated earlier, I did "play" with the tape following the directions in the manual for "re-threading" the tape. It seems to turn smoothly (at least to me - maybe not to the HP85...)

If anyone else has any ideas, I'd appreciate them. Maybe I'll try different capstan replacement coverings too...
?

-Mike


#16

Mike,

According to the 85B, service manual (June 1983) the problem may be with the tape speed circuit alignment. LED DS1 on the capstan motor assembly and phototransistor CR1 on the tape transport assembly. This would have been disturbed when you remove the capstan motor.

“Without a cartridge inserted, run the Tape Speed Test from the Service ROM. If the message {TAPE STALLED} appears proceed with step k to reposition the phototransistor”

If you have an o’scope measure at tp-4 (upper tp lower left corner of tape pca) you will need to active the drive if you do not have the service ROM (I do not have a copy) set the scope as followed:

10usec/div, 2 v/div, ac coupling --you should see 3 cycles of a sine wave the negative portion is limited. The positive peak should be at least 2.5 v and the negative peak should be a least 2v. Reposition phototransistor CR1 until the desired waveform is obtained.

If you don’t have a scope then I guess you can try it “hit or miss”

Another interesting note “if the customers computer can read tape cartridges that were reordered on the same computer but cannot read cartridges recorded on another computer the tape head maybe out of alignment. Align or replace tape drive assembly. Be sure to inform customer that the computer may no longer be able to read tapes previously recorded on that computer”


Hope this helps

Regards


JR


#17

This is GREAT information, JR, thanks!

I do not have a service manual, and didn't see it in the Museum CD set that I have. Maybe I'll have to try and find one. In the meantime, your information gives me some EXCELLENT clues on where to look next.

I've got another two HP85's from which to salvage parts.

Checking the service manual sure makes it easier to see quickly what's going on (at least in this case)!

-Mike


#18

I have the HP service manual for the 85B (june 1983) and am willing to scan or copy the manual to be included in the next revision of the museum's CD (if it is not already there) I haven't ordered a copy yet. I need and address which to submit..I am willing to make copies (scans) of any portions (no cost) for anyone that desires them.

Regards

jr

#19

This place stocks the belts:
http://timing-belt.com/urethane_polyester_mxl.html
they also have urethane-kevlar.

both the 175T80 and the 78T80.

Also, these two might be suitable for the 175T80 belt:

In neoprene-polyester:

from:http://www.mpcomponents.com/Catalog/Belts&Pulleys/NeoBelt080.asp
EPS0175A125N
.080 PCH 175 TH 1/8
EPS0175A187N
.080 PCH 175 TH 3/16 WIDE TIME

Or urethane-polyester

from:http://www.mpcomponents.com/Catalog/Belts&Pulleys/UrBelt080.asp
EPS0175A125U
.080 PCH 175 TH 1/8
EPS0175A187U
.080 PCH 175 TH 3/16 WIDE TIME


#20

I just ordered myself 7 sets of belts from Belt Corporation of America (770)887-9725 or 1-800-235-0947. www.timing-belt.com, www.beltcorp.com. They stock both the 175T80 and 78T80 in urethane-kevlar, for $2.00 and $1.65 apiece, respectively, (price for 3/16" width belts) as well as one of them in urethane-polyester. Their minimum credit card order is $25, and they cut belts to the width you specify.


#21

Chris-

Have you received the belts that you ordered and tried them yet?
I've been eagerly watching your posts, because, I too, will order the belts, if you are successful...

My ONLY concern is that with a caliper, I measure the "thickness" of the old belt to be 0.033" versus 0.045" for the new belts as indicated in the specification drawings at www.timing-belt.com. Perhaps the old belt "shrunk" over the many years. This would not be such a concern, except that the new belt does have to fit in the thin slot in the back of the printhead mechanism...

It does appear that the material of the teeth may be more important than the backing/reinforcing cording.
Do you feel the urethane-kevlar is the way to go? Doesn't urethane seem to break down over time when exposed to moisture? Would neoprene be better? Maybe it is so close as to not matter?

-Mike
p.s. I did receive a nice email from Chemi-Flex (the OEM belt supplier), and they do not supply small quantities of belts, but could possibly sell any overruns...


#22

Comments inline..

>Have you received the belts that you ordered and tried them >yet?

I have indeed received them, and just installed them. I haven't been able to test it out yet since I seem to have blown something in the power supply by inserting flexprint cabling connecting the PC boards misaligned and shorting something, but that's another story entirely. The belts are of very high quality.

>I've been eagerly watching your posts, because, I too, will >order the belts, if you are successful...
>My ONLY concern is that with a caliper, I measure the >"thickness" of the old belt to be 0.033" versus 0.045" for >the new belts as indicated in the specification drawings at >www.timing-belt.com. Perhaps the old belt "shrunk" over >the many years. This would not be such a concern, except >that the new belt does have to fit in the thin slot in the >back of the printhead mechanism...

The new belts do fit in the slot in the printhead mechanism. It's a rather snug fit, but it works.

>It does appear that the material of the teeth may be more >important than the backing/reinforcing cording.
>Do you feel the urethane-kevlar is the way to go? Doesn't >urethane seem to break down over time when exposed to >moisture? Would neoprene be better? Maybe it is so close >as to not matter?

I'm not a rubber expert, but I think neoprene probably would last longer..How much longer, I'm not sure. The sales rep didn't seem to think there would be much difference between the two. Any extra sets of belts should last a while if stored under proper conditions. Just make sure you get an 1/8" wide belt for the 175-tooth belt. You can go much wider on the shorter belt, I used 3/16", but I bought that width for the longer belt as well, and had to trim it down to 1/8" or so with a pair of fabric scissors.

-Chris


#23

Thank you very much, Chris! I've ordered the belts!
-Mike


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